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Research ArticleArticle

In Vivo Investigation in Pigs of Intestinal Absorption, Hepatobiliary Disposition, and Metabolism of the 5α-Reductase Inhibitor Finasteride and the Effects of Coadministered Ketoconazole

Anna Lundahl, Mikael Hedeland, Ulf Bondesson and Hans Lennernäs
Drug Metabolism and Disposition May 2011, 39 (5) 847-857; DOI: https://doi.org/10.1124/dmd.110.035311

Abstract

The overall aim of this detailed investigation of the pharmacokinetics (PK) and metabolism of finasteride in pigs was to improve understanding of in vivo PK for this drug and its metabolites. Specific aims were to examine the effects of ketoconazole coadministration on the PK in three plasma compartments (the portal, hepatic, and femoral veins), bile, and urine and to use these data to study in detail the intestinal absorption and the liver extraction ratio and apply a semiphysiological based PK model to the data. The pigs received an intrajejunal dose of finasteride (0.8 mg/kg) either alone (n = 5) or together with ketoconazole (10 mg/kg) (n = 5) or an intravenous dose (0.2 mg/kg) (n = 3). Plasma, bile, and urine (collected from 0 to 6 h) were analyzed with ultraperformance liquid chromatography-tandem mass spectrometry. Ketoconazole increased the bioavailability of finasteride from 0.36 ± 0.23 to 0.91 ± 0.1 (p < 0.05) and the terminal half-life from 1.6 ± 0.4 to 4.0 ± 1.1 h (p < 0.05). From deconvolution, it was found that the absorption rate from the intestine to the portal vein was rapid, and the product of the fraction absorbed and the fraction that escaped gut wall metabolism was high (fa · FG ∼1). Interestingly, the apparent absorption rate constant (ka) to the femoral vein was lower than that to the portal vein, probably because of binding and distribution within the liver. The liver extraction ratio was time-dependent and varied with the two routes of administration. After intrajejunal administration, from 1 to 6 h, the liver extraction ratio was significantly (p < 0.05) reduced by ketoconazole treatment from intermediate (0.41 ± 0.21) to low (0.21 ± 0.10).

Introduction

Finasteride is a 5α-reductase type II inhibitor used in the treatment of benign prostatic hyperplasia and male pattern baldness (Rittmaster et al., 1989; Drake et al., 1999). In the Prostate Cancer Prevention Trial finasteride was proven to prevent or delay the development of prostate cancer, but the patients who developed cancer had a higher risk to develop a more aggressive form (Thompson et al., 2003). 5α-Reductase inhibition for prostate cancer prevention has been evaluated (Kramer et al., 2009), and recently it was shown that dutasteride, another 5α-reductase inhibitor, had an effect on the risk reduction for development of prostate cancer (Andriole et al., 2010). For a drug that possibly will be used in a broad population for prevention of a disease, it is always valuable to have as much information as possible regarding its pharmacokinetics (PK) and metabolism. In two recent publications, we have investigated the plasma, biliary, and urinary PK with a particular focus on the phase I but also phase II metabolism of finasteride (Lundahl et al., 2009a,b).

Finasteride is a CYP3A4 substrate in humans, and it undergoes sequential phase I metabolism to ω-hydroxy finasteride (M1), finasteride ω-al (M2), and finasteride-ω-oic acid (M3) (Huskey et al., 1995) (Fig. 1). It is completely metabolized in vivo, and biliary excretion was suggested to be the major elimination route for the metabolites formed (Carlin et al., 1992, 1997). In previous reports, M1 was described as the major plasma metabolite and M3 as the major urinary metabolite in humans (Carlin et al., 1992). We were surprised to find that M1 was not present in quantifiable concentrations in the healthy volunteers administered finasteride before and after St. John's wort treatment, either in the normal or in the induced state (Lundahl et al., 2009a). Instead, two other hydroxy metabolites were isolated in human bile and urine (Lundahl et al., 2009b). Finasteride can be classified as a biopharmaceutical classification system class I compound (Amidon et al., 1995). It has high oral bioavailability (F = 0.8) and therefore an expected high fraction absorbed (fa >85%) (Steiner, 1996). Finasteride has low aqueous solubility (0.04 mg/ml), but it will be classified as a highly soluble drug, because the low clinical dose of 5 mg is expected to be dissolved in 250 ml of water (Loftsson and Hreinsdóttir, 2006). According to the biopharmaceutical drug disposition classification system, it will also be classified as a class I compound with high solubility and extensive metabolism (Wu and Benet, 2005).

Fig. 1.
Fig. 1.

Finasteride and the sequential formation of the two phase I metabolites M1 and M3 (Carlin et al., 1992). CYP3A4 has been identified as the major enzyme involved in the biotransformation of M1 and M3 (Huskey et al., 1995).

Even though finasteride has been on the market for almost two decades there have only been a few reports that examined its involvement in drug-drug interactions (DDIs) (Sudduth and Koronkowski, 1993; Winchell et al., 1993). In this investigation, we followed up the clinical metabolism interaction study (Lundahl et al., 2009a) because there is a need to improve understanding of the in vivo PK of finasteride and its metabolites. In an earlier series of experiments conducted by colleagues in this research group, an advanced pig model was applied (Fig. 2). The pig model enables sampling from the portal vein (VP), the hepatic vein (VH), and the femoral vein (VF) and bile collection directly from the biliary duct. This has made it possible to perform in-depth investigations on the effects of several DDIs on intestinal absorption, intestinal metabolism, liver metabolism, and hepatobiliary disposition (Petri et al., 2006; Sjödin et al., 2008; Bergman et al., 2009; Thörn et al., 2009). In this study, the model was used to examine in detail the effects of ketoconazole-inhibited CYP3A-mediated metabolism on the PK of finasteride.

Fig. 2.
Fig. 2.

A schematic diagram of the pig model, which enables the sampling of bile directly from the bile duct and blood from several sites, including the portal, hepatic, and femoral veins. In this study, finasteride was administered via a single-channel catheter directly to the jejunum (intrajejunally) or intravenously into the central venous catheter. Ketoconazole was administered intrajejunally.

The overall aim was to improve understanding of the in vivo PK for finasteride and its metabolites M1 and M3. The specific aims were the following: first, to follow the plasma PK in three plasma sites (VP, VH, and VF) and to study the consequences of ketoconazole-inhibited CYP3A-mediated metabolism on the plasma profiles for finasteride and the metabolites; second, to study the biliary and urinary excretion of finasteride and its metabolites and the consequences of ketoconazole coadministration; third, to compare intravenous with intrajejunal administration of finasteride to study the rate and extent of intestinal absorption and the effects of ketoconazole coadministration on the intestinal absorption; fourth, to compare the concentrations entering (VP) and leaving (VH) the liver to calculate the liver extraction ratio over time and follow the effects of ketoconazole-inhibited CYP3A-mediated metabolism in the liver; and fifth, to apply a semiphysiologically based PK model to the plasma data in the VP and VF to be able to study the effects of changes in specific PK parameters.

Materials and Methods

Materials.

9-Acetylanthracene, finasteride, ketoconazole, propylene glycol, and testosterone were purchased from Sigma-Aldrich (St. Louis, MO). The metabolites M1 and M3 and the internal standard (finasteride-d9) were obtained from Toronto Research Chemicals (North York, ON, Canada). The ketoconazole (Fungoral) tablets (200 mg) were produced by Janssen-Cilag (Buckinghamshire, UK). Solvents and other reagents were of analytical reagent grade and were purchased from Merck (Darmstadt, Germany). Water was purified using a Milli-Q water purification system (Millipore Corporation, Billerica, MA).

Animals and Study Design.

The investigation was approved by the local ethics committee for animal research in Uppsala, Sweden, and it included 13 castrated male pigs, 10 to 12 weeks old, of mixed breed (Hampshire, Yorkshire, and Swedish Landrace). The pigs were randomized to three groups (Table 1). A pilot study was performed for T1 and T2 on two animals, ID1 and ID2. All samples in the pilot study were analyzed, and PK data analyses were performed before continuing with the experiment by including the remaining animals. The results from the pilot study are included in the data analyses presented below.

View this table:
TABLE 1

Summary of the study design including information on the average dose administered and the average weight of the animals

Data are presented as the mean ± S.D.

Investigational Drugs.

Finasteride was administered in solution in all treatment groups. The intrajejunal dose (0.8 mg/kg) was dissolved in water containing 1% propylene glycol-ethanol (70/30; v/v) and infused into the jejunum through a catheter (1.5-mm diameter). The time taken to deliver the drug was 4.0 to 4.5 min. In T2, ketoconazole was administered at the same administration site 20 min before the finasteride dose. One ketoconazole tablet (200 mg) was suspended in 5 ml of 0.1 M HCl and, to obtain the correct dose for each animal (10 mg/kg), the dose was adjusted with a ketoconazole dispersion (20 mg/ml), depending on the weight of each pig. The time taken to deliver the ketoconazole was less than 2 min. For the intravenous administration (0.2 mg/kg), finasteride was dissolved in a total volume of 5 ml containing 1.75 ml of propylene glycol-ethanol (70:30, v/v) and 3.25 ml of isotonic saline. The solution was filtered (pore size; 0.2 μm) and administered directly into the central venous catheter. We tested to determine that the filtration of the solution did not affect the concentration of finasteride in the administered intravenous dose. The time to deliver the intravenous dose was <1 min.

Anesthesia and Surgical Procedures.

The pigs were anesthetized, and surgery was performed according to previously described methods (Petri et al., 2006; Sjödin et al., 2008; Bergman et al., 2009). The body temperature, blood gases, blood pH, hematocrit, arterial and central venous pressures, heart rate, and electrocardiographic parameters were continuously monitored during the entire experiment. The pigs underwent a tracheotomy, and the oxygen pressure was controlled by mechanical ventilation with a Servo 900C ventilator (Siemens-Elema, Solna, Sweden). Catheters were inserted into an ear vein, the right VF, the central vein, the VH, the VP, the bile duct, the small intestine, and the urinary bladder. The VH catheter was inserted through the jugular vein, and its position was controlled by fluoroscopy. To open the abdominal cavity, a midline incision was made enabling cannulation of the VP, the bile duct, and the small intestine. The surgical procedures and preparations proceeded for 90 to 120 min and, before administration of the investigational drugs, the animals were allowed to stabilize for 20 to 25 min. After 360 min of sampling, the pigs received an intravenous injection of 20 to 30 mmol of potassium chloride, and this terminated the experiment.

Sampling of Bile, Urine, and Plasma.

Blood samples were collected into lithium heparinized Vacutainers (3 ml; BD, Franklin Lakes, NJ) predose and 10, 20, 30, 40, 50, 60, 90, 135, 180, 240, 300, and 360 min after the intrajejunal dose was given and 2, 5, 10, 15, 20, 30, 45, 60, 90, 120, 135, 150, 180, 240, 300, and 360 min after injection of the intravenous dose. The blood samples were centrifuged at 2350g for 10 min (4°C), and the plasma was separated. To determine the blood/plasma ratio, extra blood samples were withdrawn from the VF after 30 and 300 min and diluted with water (1:3, v/v). Bile was continuously sampled on ice at 30-min intervals from 0 to 360 min. Urine sampling was performed in 120-min intervals from 0 to 360 min into a closed urine bag. The collected bile and urine were weighed. All samples were frozen at −20°C pending analysis.

Chemical Analysis.

The majority of the bile, plasma, and urine samples were analyzed with ultraperformance liquid chromatography (UPLC)-tandem mass spectrometry for quantification of finasteride, M1, and M3. A few plasma and blood/water samples were analyzed with high-performance liquid chromatography coupled to a UV detector (HPLC-UV) for quantification of the finasteride and ketoconazole.

UPLC-Tandem Mass Spectrometry Analysis of Finasteride and Its Metabolites in Plasma, Bile, and Urine.

To 500 μl of plasma, 200 μl of water and 100 μl of the internal standard solution (finasteride-d9) were added, followed by 3.0 ml of acetonitrile. After a vortex mix (30 s) the samples were centrifuged for 10 min. The supernatants were transferred to a new tube and evaporated under a stream of nitrogen at 50°C until approximately 100 μl remained. Then 100 μl of a solution of 0.1% formic acid (aqueous)-methanol (9/1, v/v) was added to the samples before transfer to UPLC vials. To 100 μl of bile, 300 μl of water and 100 μl of internal standard solution were added, and to 100 μl of urine, 200 μl of water and 100 μl of internal standard solution were added. The bile and urine samples were then vortex-mixed and transferred to UPLC vials. An Acquity UPLC system was coupled to a Quattro Ultima Pt tandem quadrupole mass spectrometer with an electrospray interface operating in the positive mode (Waters, Milford, MA). The column was an Acquity UPLC BEH C18 (length 50 mm, i.d. 2.1 mm, and particle size 1.7 μm; Waters) kept at 40°C. The mobile phase consisted of (A) 0.1% formic acid in water and (B) methanol. A gradient was run as follows: 12% B for 1 min, increased from 12 to 90% B for 0.20 min and then maintained at 90% B for 1.8 min, reduced from 90 to 12% B over 0.10 min, and kept constant at 12% B for 2.90 min. The total run time was 6.00 min, the flow rate was 300 μl/min, and the injection volume was 20 μl.

The three analytes were analyzed simultaneously in the same chromatographic run using a positive capillary voltage of 2.75 kV. The desolvation and source block temperatures were 350 and 120°C, and the cone and desolvation gas flows were 68 and 981 l/h, respectively. The quantifications were performed in the selected reaction monitoring mode with the collision cell filled with argon gas at a pressure of 2.9 × 10−3 mBar. The mass transitions used were m/z 373.63 → 305.30 for finasteride (collision energy 43 eV and cone voltage 81 V) with m/z 382.47 → 314.54 for the internal standard, finasteride-d9 (collision energy 45 eV and cone voltage 86 V), m/z 389.41 → 271.94 for M1 (collision energy 33 eV and cone voltage 72 V), and m/z 403.34 → 334.53 for M3 (collision energy 45 eV and cone voltage 86 V). The dwell time was 0.010 s. The calibrators and quality control samples were prepared by addition of 100 μl of a working standard solution containing all three analytes to the respective matrix. The calibration was performed by a linear curve fit (weighting factor of 1/x2) of the peak area ratio (analyte/internal standard) as a function of the concentration in the respective matrix. For plasma, the standard curve interval for finasteride was 1.2 to 2002 ng/ml, for M1 it was 2.2 to 108 ng/ml, and for M3 it was 2.2 to 110 ng/ml. For bile, the standard curve interval for finasteride was 25 to 2510 ng/ml, for M1 it was 25 to 1000 ng/ml, and for M3 it was 25 to 54,800 ng/ml. For urine, the standard curve interval for finasteride was 5.1 to 250 ng/ml, for M1 it was 11 to 1000 ng/ml, and for M3 it was 55 to 41,100 ng/ml. The precision (coefficient of variance) in plasma was ≤5.4% for finasteride and ≤15.8% for M3, in bile it was ≤8.1% for finasteride and ≤9.8% for M3, and in urine it was ≤0.3% for finasteride and ≤11.3% for M3. M1 was not present in quantifiable concentrations in plasma, bile, or urine.

HPLC-UV Analysis of Finasteride in Plasma and Blood.

Blood and plasma withdrawn at 30 and 300 min from the VF were used to determine the blood/plasma (Cb/Cp) ratio and the fraction unbound (Cu/Cp). To measure the unbound finasteride concentration (Cu), the plasma was centrifuged (40 min at 10,000g) with Amicon Ultra centrifugal filters (0.5 ml, 10 K). Nonspecific binding to the filter device was measured by centrifugation of an aqueous solution of finasteride. The total plasma concentrations (Cp) and blood concentrations (Cb) were determined. Five hundred microliters of plasma/blood were precipitated with 500 μl of acetonitrile and centrifuged (10,000g, 10 min). After dilution with water, the samples were loaded onto Oasis HLB 3cc columns. After a column wash with water, the analytes were eluted from the columns with methanol-acetonitrile (v/v, 1:1) that, then, was evaporated under a steam of nitrogen while the samples were heated to 50°C. The analytes were dissolved in 150 μl of mobile phase containing the internal standard, testosterone, and 100 μl was injected into the HPLC-UV system that consisted of a Shimadzu pump LC-10AD, a Waters 717 plus Autosampler, a Spectra 100 UV detector (λ = 210 nm) (Thermo Fisher Scientific, Waltham, MA), and a C-18 Hypersil Gold column (250 × 4.6 mm, 5 μm; Thermo Fisher Scientific) with a guard column. The isocratic mobile phase consisted of 60% 20 mM ammonium acetate, 40% acetonitrile, and 0.1% trifluoroacetic acid and was delivered at a flow of 1 ml/min. The linear concentration range used for the calibration curve was 0.003 to 1 μM.

HPLC-UV Analysis of Ketoconazole in Plasma.

The analysis of ketoconazole in plasma from the VP and the VF was performed according to a method described previously (Vertzoni et al., 2006). One hundred microliters of plasma was precipitated with 100 μl of acetonitrile containing the internal standard (9-acetylanthracene) and centrifuged (10,000g, 10 min), and 100 μl of the supernatant was directly injected into the HPLC-UV (λ = 240 nm) system, described above. The mobile phase consisted of 70% methanol, 29% water, and 1% diethylamine and was isocratically delivered at a flow of 1 ml/min. The linear concentration range used for the calibration curve was 0.04 to 50 μM.

PK Data Analysis.

The PK parameters were calculated from the plasma and bile concentration-time profiles by zero-, one-, or two-compartment analyses conducted using WinNonlin software (version 5.2; Pharsight Corporation, Mountain View, CA). For the noncompartment analyses (NCA), the AUC was estimated using the linear trapezoidal method for ascending values and the log trapezoidal method for descending values. The AUC0–6 h was calculated from time 0 until the last measured concentration point (Clast). AUC0–∞was calculated by extrapolating the curve to infinity by adding Clast/λz to AUC0–6 h, where λz is the first-order terminal disposition rate constant. The peak concentration in plasma/bile (Cmax) and the time taken to reach Cmax (tmax) were obtained directly from the plasma concentration-time profiles. Concentrations below the lower limit of quantification before Cmax were set to zero and were otherwise (after Cmax) excluded from the calculations. The terminal half-life (t1/2) was calculated as ln2/λz. After the intravenous administration, the apparent volume of the distribution in the steady state (Vss) was calculated as MRT · CL, where the mean residence time (MRT) was calculated as the area under the first moment curve (AUMC0–6 h) divided by AUC0–6 h. The total clearance (CL) after intravenous administration was calculated as in eq. 1: Embedded Image

Because the hepatic clearance (CLH) was assumed to be equal to the total CL after intravenous administration, the liver extraction ratio (EH) was calculated as in eq. 2: Embedded Image with a liver blood flow (QH) in pig of 52 ml/min/kg (Nordgren et al., 2002) and where Cb/Cp is the measured blood/plasma ratio for finasteride in pig. In all three of the groups given different treatments, EH could also be calculated by comparing the plasma concentrations in the VP and the VH at each time point or by using partial AUCs or the AUC0–6 h (eqs. 3 and 4): Embedded Image Embedded Image

CLH could also be calculated from EH (from eq. 3), by rearranging eq. 2. The oral bioavailability in T1 and T2 was calculated as in eq. 5: Embedded Image where AUCVF, i.v. was an average AUC (n = 3). The fraction of the dose excreted into bile (fbile) during the 6 h of sampling was determined from the total amount of finasteride or M3 excreted into bile divided by the intrajejunal/intravenous dose. The fraction of the dose excreted into urine (furine) during the 6 h of sampling was calculated as the total amount of finasteride or M3 excreted into urine divided by the intrajejunal/intravenous dose. The apparent biliary clearance was calculated by comparing the amount of finasteride/M3 excreted to the bile with the AUCVP (eq. 6): Embedded Image and the renal clearance was calculated with eq. 7. Embedded Image

For the one- and two-compartment analyses, WinNonlin models were used. Model 8 (bolus input, first-order output) was used for the two-compartment modeling of the intravenous data and C1, C2, λ1, and λ2 were estimated. C1 and λ1 describe the initial slope of the curve and C2 and λ2 the terminal slope of the curve (change in concentration over time = C1 · eλ1t + C2 · eλ2t). Model 4 (first-order input, first-order output, and lag time) was used for the one-compartment modeling of the intrajejunal data and the absorption rate (k01) and the elimination rate (k10) constants were estimated. The coefficient of variance percentage of the estimated parameters, total statistics for the models, and curve fits were compared to evaluate the models.

Deconvolution of data was performed using WinNonlin software. The response function, r(t), was derived from the concentration-time profiles for the VP and VF after T1 and T2. The weight function, w(t), was derived from the two-compartment analyses of the concentration-time profiles in the VP and the VF after intravenous administration. C1 and C2 were multiplied by a factor of 4 to compensate for the 4 times lower intravenous dose than the intrajejunal dose (Table 1). The input function, i(t) was derived from deconvolution: i(t) = r(t)//w(t). The initial rate was set to zero, automatic smoothing was used, and the number of output data terms to be calculated was set to 101.

Semiphysiological PK Model for Finasteride.

The PK of finasteride in the VP and the VF after intrajejunal administration, for T1 and T2, were described by a semiphysiological PK model composed of compartments for the gut wall, the portal vein, the liver, the central vein, and the peripheral distribution compartment. The model is described in detail in the supplemental data. It was built in Berkeley Madonna (version 8.3; University of California, Berkeley, CA) and was derived through the combination of previously described models (Fang et al., 2000; Yang et al., 2003; Zhang et al., 2009; Rowland Yeo et al., 2010)

Statistics.

Unpaired, two-sided Student's t tests were performed to evaluate the differences between the treatments. For tmax, the two-sample Mann-Whitney test was used. Differences were considered to be statistically significant when p < 0.05. It was determined that five animals in each group were required to detect a 2-fold difference in the plasma AUC with 80% power (α = 0.05). This calculation was based on results obtained from the pilot study and an assumed large S.D. All data were included in the statistical analysis for all parameters, except t1/2. For this parameter, outlier tests were performed using a general linear model and the software Minitab 15.1 (Minitab Inc., State College, PA) to calculate the deleted studentized residuals (the residual divided by the S.D. of the residual minus one observation) and Cook's distances. A value was excluded from the data analysis if it had a deleted studentized residual of greater than 2.0 and an unusual value for Cook's distance; the comparisons were made for the latter by composing a graph of distances versus observations (time series plot).

Results

This report includes data for finasteride and M3 in plasma (VP, VH, and VF) and in bile and urine. M1 was not present in quantifiable concentrations in bile, plasma, or urine in any of the three groups of treatment. The AUC0–6 h (from NCA) was used for all calculations (eqs. 1–7), because the extrapolated areas for AUC0–∞ (NCA) were considered to be too large (>25%) to be used with confidence. However, the AUC0–6 h (NCA) was not significantly different from those obtained with the AUC0–∞ (NCA) or from the one- or two-compartment analysis.

Plasma PK and Biliary and Urinary Excretion of Finasteride and M3 after Intravenous Administration.

In the intravenous group, the plasma concentration-time profiles for finasteride in the VP and the VF were well described by a two-compartment PK model (Fig. 3A; Table 2). These data were used for the deconvolution and the semiphysiological model. For VH, the profile (after intravenous administration) was not well described by a compartment PK model. In the intravenous group, the CL and EH for finasteride were low (Table 3). The presence of M3 in the plasma (VF) was low compared with the presence of finasteride indicated by an AUCVF, 0–6 h ratio (M3/finasteride) of 0.12 (range 0.08–0.13) (Table 3). M3 was continuously formed during the 6 h of the experiment and, therefore, the estimations of Cmax, tmax, and t1/2 were uncertain (Fig. 3A). In the intravenous group, a low amount of unchanged finasteride was excreted to bile and urine during the 6-h-long experiment (Tables 4 and 5). M3 was excreted into both bile and urine after intravenous administration, but with a large interindividual variation (Tables 4 and 5).

Fig. 3.
Fig. 3.

A, finasteride (Fin) and finasteride-ω-oic acid (M3) in the VP and VF after intravenous administration (n = 3). B, finasteride in the VP after intrajejunal administration without (T1) and with (T2) ketoconazole coadministration (n = 5). C, finasteride in the VF for T1 and T2 (n = 5). D, M3 in the VF for T1 and T2 (n = 5). E and F, individual finasteride plasma concentrations in the VF for T1 (E) and for T2 (F). The data in A, E, and F are depicted on a semilogarithmic scale. The concentration-time points in A to D are displayed as the mean ± S.E.

View this table:
TABLE 2

Pharmacokinetic parameters of finasteride and M3 after intravenous administration

n = 3.

View this table:
TABLE 3

Liver extraction ratio, bioavailability, hepatic clearance, volume of distribution, total clearance, and metabolite/parent AUC ratio for finasteride after intravenous and intrajejunal administration with (T2) and without (T1) ketoconazole coadministration

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TABLE 4

Biliary excretion, apparent biliary clearance, and comparison bile/plasma ratio of finasteride and M3 after intravenous and intrajejunal administration with (T2) and without (T1) ketoconazole coadministration

View this table:
TABLE 5

Renal excretion and renal clearance of finasteride and M3 after intravenous and intrajejunal administration with (T2) and without (T1) ketoconazole coadministration

Effect of Ketoconazole on the Plasma Exposure of Finasteride and M3, after Intrajejunal Administration (T1 and T2).

The plasma exposure (AUCs) of finasteride was increased (p < 0.05) and the plasma exposure of M3 was decreased (p < 0.05) at all three sampling sites in T2 (Fig. 3, B–D; Table 6). Ketoconazole increased the bioavailability and prolonged the t1/2 for finasteride (Tables 3 and 6). The AUCVF, 0–6 h ratio (M3/finasteride) decreased from 1.4 (range 0.13–4.1) to 0.06 (range 0.04–0.09) for T1 and T2, respectively (Table 3). There was a large interindividual variation in the plasma concentration-time profiles in the T1 group (Fig. 3E), which was reduced in the T2 group (Fig. 3F). For t1/2 a separate statistical analysis was conducted to test whether any of the values could be considered to be outliers. Two values, t1/2 for ID13 in T1 and for ID2 in T2, were concluded to be outliers and removed before the Student's t test was performed. All other data (plasma, biliary, and urinary) for ID13 and ID2 were included in the data analysis.

View this table:
TABLE 6

Pharmacokinetic parameters of finasteride and M3 after intrajejunal administration with (T2) and without (T1) ketoconazole coadministration

n = 5.

The apparent absorption kinetics of finasteride from the gut lumen to the VP and the VF were investigated both by one-compartment analysis (k01) of the concentration-time profiles and by deconvolution (ka, t1/2, abs) of the intrajejunal data to intravenous data (Fig. 4; Table 6). The absorption half-life (t1/2, abs), obtained from deconvolution from the intestine to the VP was short, and there was an increased t1/2, abs with ketoconazole coadministration from 2 ± 1 to 4 ± 2 min (p < 0.05), for T1 and T2, respectively. From the intestine to the VP the cumulative input fraction was derived from deconvolution, and this represents both the fractions of the dose absorbed and the fraction that escapes gut wall metabolism (fa · FG). This fraction (fa · FG) was close to 1 (i.e., 100%) in T1, and this was not significantly affected by ketoconazole in T2 (Fig. 4, A and C). The absorption to VP started immediately after both T1 and T2 without any lag time in six animals and with a delay ranging from 1 to 9 min in four animals. The apparent absorption rate constant (ka), derived from deconvolution, from the intestine to the VF was lower (p < 0.05 in T1 and T2) compared with the ka to the VP (Fig. 4B; Table 6). In addition, for the absorption to the VF there was a lag time of 13 ± 4 and 10 ± 1 min for T1 and T2, respectively. It was concluded that the input rate to the VF was significantly affected by the distribution and that the input rate to the VP better described the intestinal absorption kinetics. The cumulative input fraction (Fig. 4D) from the intestine to the VF represents the bioavailability (F), and this was significantly (p < 0.05) increased by ketoconazole (Table 3).

Fig. 4.
Fig. 4.

Input rate to the VP (A) and to the VF (B) with (T2) and without (T1) ketoconazole. The slopes in the linear part of the curves represent ka. Cumulative input fraction of finasteride after T1 and T2 to the VP (C) and to the VF (D). The data were derived from deconvolution of intravenous to intrajejunal data and are presented as the mean ± S.E.

By calculating EH with eq. 4 for each time point or using eq. 3 with the partial AUCs for 0 to 1 h, 1 to 2 h, and so on, it was found that EH varied over time (Fig. 5) in all of the treatment groups. After intravenous administration, EH was high (>0.7) at the first time point (5 min), and, thereafter, it was low, continuously (<0.3). After intrajejunal administration, EH had an intermediate value (0.3 < EH < 0.7) during the first hour after the finasteride administration with almost identical values; 0.58 ± 0.2 and 0.61 ± 0.2, in T1 and T2, respectively. However, from 1 to 6 h the EH based on partial AUCs per hour was reduced from 0.41 ± 0.24 to 0.21 ± 0.10 in T1 and T2, respectively (p < 0.05, n = 25). In Table 3, the values for EH calculated from eq. 3 (AUC0–6 h) are presented. EH (0–6 h) was significantly (p < 0.05) lower after intravenous than intrajejunal administration.

Fig. 5.
Fig. 5.

Liver extraction ratios for finasteride calculated from the comparison of concentrations in the portal vein to the concentrations in the hepatic vein (eq. 4) after intravenous (IV) (n = 3) and intrajejunal administration with (T2) and without (T1) ketoconazole coadministration (n = 5). The extraction ratios are presented as the mean ± S.E.

Effect of Ketoconazole on the Biliary and Urinary Excretion of Finasteride and M3 after Intrajejunal Administration (T1 and T2).

In total, in both groups, the fraction of the dose excreted to bile and urine as unchanged finasteride during the 6-h-long experiment was ≤0.4% of the amount administered (Tables 4 and 5). However, in T2, there was a tendency toward increased biliary excretion of finasteride (Fig. 6A) and the amount of finasteride excreted to urine was significantly (p < 0.05) increased (Fig. 6C). The interindividual variation in the amount of excreted M3 to bile (Fig. 6B) and urine (Fig. 6D) was large, and no statistically significant difference between T1 and T2 could be determined. M3 was probably actively excreted to bile against a concentration gradient and the AUC ratios (bile/plasma) of the total concentrations were 100 times higher in bile (Table 4). This ratio was not affected by ketoconazole coadministration. The AUCbile/AUCVP ratio for finasteride was close to 1 in T1, and this indicated that finasteride was excreted to bile by passive diffusion.

Fig. 6.
Fig. 6.

Accumulated amounts of finasteride (Fin) (A) and M3 (B) in bile after intravenous (IV) (n = 3) and intrajejunal administration with (T2) and without (T1) ketoconazole coadministration (n = 5). Accumulated amounts of finasteride (C) and M3 (D) in urine after administration of finasteride in the IV, T1, and T2 groups. The data are presented as the mean ± S.E.

Blood/Plasma Ratio and Fraction Unbound of Finasteride.

The ratio Cb/Cp was determined in two individuals (ID4 and ID13) from samples withdrawn at 30 and 300 min and was determined to be 1.03 ± 0.23. The hematocrit was 27 ± 3% (n = 36, 10 animals). The fraction unbound for finasteride in pig plasma was 0.17 ± 0.15 (n = 5, 3 animals).

Ketoconazole PK in Plasma (T2).

The intrajejunal administration of ketoconazole resulted in a Cmax of 9 ± 3 μM in the VP and of 3 ± 1 μM in the VF. See the plasma PK data for ketoconazole in the VP and VF in Table 7.

View this table:
TABLE 7

Pharmacokinetic plasma parameters for ketoconazole

Semiphysiological PK Model.

A semiphysiological PK model could describe the observed data in VP and VF for T1 and T2 (Fig. 7, A–D). First, a model that described the mean plasma concentration-time curves in the VP and the VF for the control group, T1, was developed. The following parameters were found to be of importance and were adjusted to improve the correspondence of the observed mean and the model concentration-time curves: Vpv, kgl, kpv, Qh, Vmax gw, Km, Vmax, and fa (Table 8). Second, for the description of the mean curves for T2, the measured ketoconazole Cmax values in the VP and the VF were added as the inhibitor concentration in the gut wall and liver, and values of Ki and fu for ketoconazole, obtained from the literature, were included, see supplemental data and Table 8 for detailed information. When these data were added to the model, the interaction was not completely described. After increasing the inhibitor concentration in the liver, the interaction was better described. Variations in the gut wall inhibitor concentration did not have a significant effect on the plasma concentration-time profiles. All parameters were kept as for T1 (Table 8) except for the volume of the central venous compartment (Vcent) (see eq. 1, supplemental data) that had to be somewhat decreased. The final model did give a fairly good description of the way in which the plasma concentration-time profiles of finasteride were affected by inhibition of the metabolism of finasteride in the gut wall and the liver (Fig. 7, E and F; Table 8).

Fig. 7.
Fig. 7.

Individual and modeled plasma concentration-time curves for finasteride: A, in the VF and the central compartment (Ccent) without ketoconazole coadministration (T1); B, in the VP and the portal vein compartment (Cpv) after T1; C, in the VF and the central compartment with ketoconazole coadministration (T2); and D, in the VP and the portal vein compartment after T2. Average observed and model-based plasma concentration-time curves for comparison between T1 and T2 in the VF (E) and in the VP (F).

View this table:
TABLE 8

Parameters for the semiphysiologically based pharmacokinetic model for T1 and T2

Discussion

In this study, the effects of ketoconazole coadministration on the PK in three plasma compartments (VP, VH, and VF) were examined along with the biliary and urinary excretion of finasteride and its metabolites. In addition, the intestinal absorption and the liver extraction ratio for finasteride were studied, and the effects of ketoconazole coadministration were examined. The major findings were that ketoconazole coadministration caused an increased F and a prolonged t1/2 for finasteride and decreased plasma exposure (AUC and Cmax) for M3. Metabolism in the liver (CLH and EH) and not in the gut wall was suggested to be of major importance for this DDI, and this fact is discussed further below. The sequential route of metabolism from finasteride to M3 was almost completely inhibited and the AUCVF, 0–6 h ratio (M3/finasteride) decreased. This finding confirmed that CYP3A is important for the plasma exposure of finasteride and for the sequential formation of M3. It was possible to build a semiphysiological PK model, including five compartments (the gut wall, portal vein, liver, peripheral vein, and the central vein) to describe the plasma concentration-time profiles in the VP and the VF in T1 and to sufficiently describe the profiles in T2.

Finasteride was found to have a route- and time-dependent EH (Fig. 3) in pigs. The EH was intermediate and almost high the first hour after intrajejunal administration of the drug, and this was when the concentrations of finasteride were high in the VP during the absorption and distribution phases. Ketoconazole had an effect on the EH, which decreased during the elimination phase from 1 to 6 h. Finasteride has been reported to have a linear PK in humans (Ohtawa et al., 1991), except when low doses (0.2 mg) were administered (Suzuki et al., 2010). The finding of a higher value for EH at higher VP concentrations is unexpected and not easily explained. The same type of phenomenon was found also for R- and S-verapamil when the gut wall metabolism was inhibited by ketoconazole and the AUC in the VP was increased (Thörn et al., 2009). As with finasteride, an increased EH was observed with the higher VP concentrations, and it was suggested to be the result of saturable plasma protein binding for R- and S-verapamil (Thörn et al., 2009). A possible hypothesis for the finasteride observation could also be a temporary saturation of plasma protein binding that would increase the fu and thereby the CLH. An explanation for the finding that the metabolism in the liver does not seem to be saturated with the high incoming VP concentrations is that finasteride could distribute within the liver, possibly bind to the liver tissue components, and cause a “sink” in the liver, which reduces the risk of saturating the metabolism (Rubin and Tozer, 1986). On the basis of previous experiments and the careful monitoring of the physiological parameters of the animals in this laboratory, the liver blood flow is expected to not vary over time and to be comparable among the pigs in the different groups (Nordgren et al., 2002). Worthy of mention, the biliary excretion data of finasteride does not contribute to explaining this finding. The observation that the k01 and ka to the VF was lower compared with the k01 and ka to the VP correlates with the theory that there is a mechanism, possibly binding and distribution within the liver, that delays the absorption (input rate, hour−1) to the VF and that takes place the first hour after intrajejunal administration of finasteride (Fig. 2; Table 6).

It is an interesting observation that the input rate, indicated by ka and tmax, into VF was lower than to the corresponding parameter to VP. In oral drug product development, it is of importance to establish in vitro-in vivo correlation of drug absorption, and this is always based on plasma concentration-time data from a peripheral vein. Therefore, the observation in this study that there exists a difference in the absorption rate constant (ka) based on the plasma compartments in the VP and VF might be of importance for assessment of in vivo bioequivalence, especially Cmax and tmax. It has the potential to explain why an in vitro-in vivo correlation is difficult to establish for some oral pharmaceutical products.

In pigs, finasteride had a Vss of 25 liters (1.0 l/kg), a total plasma CL of 11 l/h (0.45 l · h−1 · kg−1), and an F of 0.4. The corresponding parameters in humans were 76 liters (1.1 l/kg), 10 l/h (0.14 l · h−1 · kg−1) (for a 70-kg individual), and 0.8 (Steiner, 1996), respectively. The total plasma CL (liters per hour per kilogram) was 3 times higher in pigs than in humans, and Vss (liters per kilogram) was almost identical. The F was lower in pigs compared with that in humans, and there can be two explanations for this finding, either a difference in fa · FG or a difference in FH between humans and pigs. The most plausible explanation is that the FH is lower in pigs than in humans as reflected by the 3 times higher total plasma CL (liters per hour per kilogram) in pigs. CYP3A4 has been identified as the major enzyme responsible for the sequential formation of M3 (Huskey et al., 1995). In a recent report, the most abundant cytochrome P450 (P450) subfamilies in pigs were found to be CYP2A, 2D, 2C, and 3A, and this was identified using matrix-assisted laser desorption ionization/time of flight mass spectrometry (Achour et al., 2010). Four enzymes in the CYP3A family have been cloned from pigs (domestic and minipig) [CYP3A22, CYP3A29 (Nissen et al., 1998), CYP3A39, and CYP3A46], with 75 to 78% amino acid identity to human CYP3A4 and 82 to 84% nucleotide similarity (Sakuma et al., 2004). Enterocytes, hepatocytes, and liver and intestinal microsomes from pigs have been used to study drug metabolism, and, even though the CYP3A enzymes are not identical to CYP3A4, similar activity and a corresponding rate of metabolism have been observed for substrates such as testosterone and tacrolimus (Olsen et al., 1997; Skaanild and Friis, 1997; Bader et al., 2000). Inhibition of CYP3A-mediated metabolism by ketoconazole has been reported in pig intestinal microsomes (Lampen et al., 1996). In addition, in two previously reported pig studies, ketoconazole inhibited the stereoselective gut wall metabolism of the CYP3A4 substrates S- and R-verapamil (Thörn et al., 2009) and the metabolism of tacrolimus (Sano et al., 2002). This study gives further evidence that the pig is a relevant model animal for CYP3A substrates.

The pigs were kept under anesthesia, and the body temperature, blood pressure, blood pH, and blood gases were carefully monitored by an animal nurse during the experiment (Petri et al., 2006; Sjödin et al., 2008; Bergman et al., 2009). The splanchnic blood flow has been monitored with indocyanine green measurements in pigs that were anesthetized with the same drugs and at the same laboratory (Nordgren et al., 2002). The splanchnic blood flow was 51 ± 7 ml · min−1 · kg−1 at the starting point and 49 ± 4 ml · min−1 · kg−1 after the 4-h experiment. Seven different drug substances (Sjödin et al., 2008) were used in this study to cause anesthesia and pain relief. Four of these drugs (ketamine, pancuronium, tiletamine, and zolazepam) are known to be metabolized by P450 enzymes or to affect P450-mediated metabolism (Wong and Bandiera, 1998; Hijazi and Boulieu, 2002; Nagashima et al., 2005). All pigs received identical anesthesia and analgesia in combination with the drugs under investigation, and this makes it possible to compare the data among the groups.

Finasteride was excreted in its unchanged form to a minor extent into bile and urine (<0.4% in all treatment groups) in pigs, which was in agreement with the biliary and urinary excretion in humans (Lundahl et al., 2009a). It was also in agreement with a previous clinical study in which 57 and 39% of a 14C-labeled finasteride oral dose was excreted as metabolites to feces and urine, respectively (Carlin et al., 1992). Unfortunately, M1 was detected but was not present in quantifiable concentrations. Instead of M1, two other hydroxy metabolites were detected in urine and bile from the pigs (Lundahl et al., 2009b). The novel data from this pig study indicate that not only urinary excretion but also biliary excretion can be of importance for M3. The high (Table 4) AUC ratio of M3 in bile/VP and bile/VH indicated that carrier-mediated transporter proteins are probably involved in transporting M3 from the hepatocytes to bile. The high bile/plasma ratio was in agreement with our human study when the bile/plasma AUC ratio was 30-fold. Biliary excretion of finasteride in pig was probably driven by diffusion with an AUCbile/AUCVP ratio close to 1 (Table 4).

A first attempt to simultaneously investigate the plasma concentrations in two of the measured plasma compartments was made by building a semiphysiological PK model, which nicely described the plasma concentration-time curves in the VP and the VF after T1 and the extent of the DDI in T2. The DDI was first underpredicted when the measured Cmax for ketoconazole in the VP and the VF were used as the gut wall (Igw) and liver (Iliver) inhibitor concentrations, respectively. Then, when the total inhibitor concentration in the liver was increased, from 3 to 6.5 μM, the DDI was better predicted (Fig. 7). Increasing the inhibitor concentration in the gut wall was not found to be relevant for improving the prediction. To conclude, when the semiphysiological PK model was used to describe the data, an inhibitor concentration in the liver between Cmax in VP and VF was found to be most relevant.

In conclusion, ketoconazole caused an increased F and prolonged the t1/2 for finasteride, and this was determined to be the result of inhibited liver metabolism and reduced CLH and EH. The extent of transport of finasteride from the gut lumen to the VP was high already in the control group and not significantly affected by ketoconazole. This finding suggested a minor contribution of gut wall metabolism and a high intestinal permeability. Of interest, it was found that the rate constant (ka) to the VP was higher compared with that to the VF, and this was possibly caused by binding or distribution within the liver. A semiphysiologically based PK model was applied to describe the VP and the VF plasma concentration-time profiles in T1 and accurately described the effects of ketoconazole inhibition of the gut wall and liver metabolism in T2. The PK of finasteride in pig showed many similarities to the PK in humans, and the data achieved in this study could be used to better understand the PK and DDIs for finasteride in humans.

Authorship Contributions

Participated in research design: Lundahl and Lennernäs.

Conducted experiments: Lundahl, Hedeland, and Bondesson.

Contributed new reagents or analytic tools: Hedeland and Bondesson.

Performed data analysis: Lundahl.

Wrote or contributed to the writing of the manuscript: Lundahl and Lennernäs.

Acknowledgments

We thank Anders Nordgren for help during the pig experiments (anesthesia, surgery, monitoring, and others). We also thank Elisabeth Fredriksson for help with the analyses of the biological samples.

Footnotes

  • Article, publication date, and citation information can be found at http://dmd.aspetjournals.org.

    doi:10.1124/dmd.110.035311.

  • ↵Embedded Image The online version of this article (available at http://dmd.aspetjournals.org) contains supplemental material.

  • ABBREVIATIONS:

    PK
    pharmacokinetic(s)
    M1
    ω-hydroxy finasteride
    M2
    finasteride ω-al
    M3
    finasteride-ω-oic acid
    DDI
    drug-drug interaction
    VP
    portal vein
    VH
    hepatic vein
    VF
    femoral vein
    T1
    treatment 1
    T2
    treatment 2
    UPLC
    ultraperformance liquid chromatography
    HPLC
    high-performance liquid chromatography
    NCA
    noncompartment analyses
    AUC
    area under the plasma/bile concentration-time curve
    P450
    cytochrome P450
    CL
    clearance.

  • Received July 9, 2010.
  • Accepted February 11, 2011.

References

  1. ↵
    1. Achour B,
    2. Rostami-Hodjegan A,
    3. Barber J
    (2010) Assessing abundance of cytochrome P450 enzymes using mass spectrometry based methods: analysis of porcine liver (Poster), in Drug Metabolism Discussion Group Meeting; 2010 Sept 15–17; Canterbury, UK. DMDG, Thurmaston, Leicester, England.
  2. ↵
    1. Amidon GL,
    2. Lennernäs H,
    3. Shah VP,
    4. Crison JR
    (1995) A theoretical basis for a biopharmaceutic drug classification: the correlation of in vitro drug product dissolution and in vivo bioavailability. Pharm Res 12:413–420.
    OpenUrlCrossRefPubMed
  3. ↵
    1. Andriole GL,
    2. Bostwick DG,
    3. Brawley OW,
    4. Gomella LG,
    5. Marberger M,
    6. Montorsi F,
    7. Pettaway CA,
    8. Tammela TL,
    9. Teloken C,
    10. Tindall DJ,
    11. et al
    . (2010) Effect of dutasteride on the risk of prostate cancer. N Engl J Med 362:1192–1202.
    OpenUrlCrossRefPubMed
  4. ↵
    1. Bader A,
    2. Hansen T,
    3. Kirchner G,
    4. Allmeling C,
    5. Haverich A,
    6. Borlak JT
    (2000) Primary porcine enterocyte and hepatocyte cultures to study drug oxidation reactions. Br J Pharmacol 129:331–342.
    OpenUrlCrossRefPubMed
  5. ↵
    1. Bergman E,
    2. Lundahl A,
    3. Fridblom P,
    4. Hedeland M,
    5. Bondesson U,
    6. Knutson L,
    7. Lennernäs H
    (2009) Enterohepatic disposition of rosuvastatin in pigs and the impact of concomitant dosing with cyclosporine and gemfibrozil. Drug Metab Dispos 37:2349–2358.
    OpenUrlAbstract/FREE Full Text
  6. ↵
    1. Carlin JR,
    2. Christofalo P,
    3. Arison BH,
    4. Ellsworth RE,
    5. Rosegay A,
    6. Miller RR,
    7. Chiu SH,
    8. VandenHeuvel WJ
    (1997) Disposition and metabolism of finasteride in dogs. Drug Metab Dispos 25:100–109.
    OpenUrlAbstract/FREE Full Text
  7. ↵
    1. Carlin JR,
    2. Höglund P,
    3. Eriksson LO,
    4. Christofalo P,
    5. Gregoire SL,
    6. Taylor AM,
    7. Andersson KE
    (1992) Disposition and pharmacokinetics of [14C]finasteride after oral administration in humans. Drug Metab Dispos 20:148–155.
    OpenUrlAbstract
  8. ↵
    1. Drake L,
    2. Hordinsky M,
    3. Fiedler V,
    4. Swinehart J,
    5. Unger WP,
    6. Cotterill PC,
    7. Thiboutot DM,
    8. Lowe N,
    9. Jacobson C,
    10. Whiting D,
    11. et al
    . (1999) The effects of finasteride on scalp skin and serum androgen levels in men with androgenetic alopecia. J Am Acad Dermatol 41:550–554.
    OpenUrlPubMed
  9. ↵
    1. Fang J,
    2. McKay G,
    3. Hubbard JW,
    4. Hawes EM,
    5. Midha KK
    (2000) Dose staggering as a strategy to reduce drug–drug interactions due to reversible enzyme inhibition between orally administered drugs with high first pass effect: a computer simulation study. Biopharm Drug Dispos 21:249–259.
    OpenUrlCrossRefPubMed
  10. ↵
    1. Hijazi Y,
    2. Boulieu R
    (2002) Contribution of CYP3A4, CYP2B6, and CYP2C9 isoforms to N-demethylation of ketamine in human liver microsomes. Drug Metab Dispos 30:853–858.
    OpenUrlAbstract/FREE Full Text
  11. ↵
    1. Huskey SW,
    2. Dean DC,
    3. Miller RR,
    4. Rasmusson GH,
    5. Chiu SH
    (1995) Identification of human cytochrome P450 isozymes responsible for the in vitro oxidative metabolism of finasteride. Drug Metab Dispos 23:1126–1135.
    OpenUrlAbstract
  12. ↵
    1. Ishii Y,
    2. Mukoyama H,
    3. Ohtawa M
    (1994) In vitro biotransformation of finasteride in rat hepatic microsomes: isolation and characterization of metabolites. Drug Metab Dispos 22:79–84.
    OpenUrlAbstract
  13. ↵
    1. Kramer BS,
    2. Hagerty KL,
    3. Justman S,
    4. Somerfield MR,
    5. Albertsen PC,
    6. Blot WJ,
    7. Ballentine Carter H,
    8. Costantino JP,
    9. Epstein JI,
    10. Godley PA,
    11. et al
    . (2009) Use of 5-α-reductase inhibitors for prostate cancer chemoprevention: American Society of Clinical Oncology/American Urological Association 2008 Clinical Practice Guideline [published erratum appears in J Clin Oncol 27:2742, 2009]. J Clin Oncol 27:1502–1516.
    OpenUrlAbstract/FREE Full Text
  14. ↵
    1. Lampen A,
    2. Christians U,
    3. Gonschior AK,
    4. Bader A,
    5. Hackbarth I,
    6. von Engelhardt W,
    7. Sewing KF
    (1996) Metabolism of the macrolide immunosuppressant, tacrolimus, by the pig gut mucosa in the Ussing chamber. Br J Pharmacol 117:1730–1734.
    OpenUrlCrossRefPubMed
  15. ↵
    1. Loftsson T,
    2. Hreinsdóttir D
    (2006) Determination of aqueous solubility by heating and equilibration: a technical note. AAPS PharmSciTech 7:E4.
    OpenUrlPubMed
  16. ↵
    1. Lundahl A,
    2. Hedeland M,
    3. Bondesson U,
    4. Knutson L,
    5. Lennernäs H
    (2009a) The effect of St. John's wort on the pharmacokinetics, metabolism and biliary excretion of finasteride and its metabolites in healthy men. Eur J Pharm Sci 36:433–443.
    OpenUrlCrossRefPubMed
  17. ↵
    1. Lundahl A,
    2. Lennernäs H,
    3. Knutson L,
    4. Bondesson U,
    5. Hedeland M
    (2009b) Identification of finasteride metabolites in human bile and urine by high-performance liquid chromatography/tandem mass spectrometry. Drug Metab Dispos 37:2008–2017.
    OpenUrlAbstract/FREE Full Text
  18. ↵
    1. Nagashima A,
    2. Tanaka E,
    3. Inomata S,
    4. Honda K,
    5. Misawa S
    (2005) A study of the in vitro interaction between lidocaine and premedications using human liver microsomes. J Clin Pharm Ther 30:185–188.
    OpenUrlCrossRefPubMed
  19. ↵
    1. Nissen PH,
    2. Winterø AK,
    3. Fredholm M
    (1998) Mapping of porcine genes belonging to two different cytochrome P450 subfamilies. Anim Genet 29:7–11.
    OpenUrlCrossRefPubMed
  20. ↵
    1. Nordgren A,
    2. Karlsson T,
    3. Wiklund L
    (2002) Glutamine concentration and tissue exchange with intravenously administered alpha-ketoglutaric acid and ammonium: a dose-response study in the pig. Nutrition 18:496–504.
    OpenUrlCrossRefPubMed
  21. ↵
    1. Ohtawa M,
    2. Morikawa H,
    3. Shimazaki J
    (1991) Pharmacokinetics and biochemical efficacy after single and multiple oral administration of N-(2-methyl-2-propyl)-3-oxo-4-aza-5α-androst-1-ene-17β-carboxamide, a new type of specific competitive inhibitor of testosterone 5α-reductase, in volunteers. Eur J. Drug Metab Pharmacokinet 16:15–21.
    OpenUrlPubMed
  22. ↵
    1. Olsen AK,
    2. Hansen KT,
    3. Friis C
    (1997) Pig hepatocytes as an in vitro model to study the regulation of human CYP3A4: prediction of drug-drug interactions with 17 alpha-ethynylestradiol. Chem Biol Interact 107:93–108.
    OpenUrlCrossRefPubMed
  23. ↵
    1. Petri N,
    2. Bergman E,
    3. Forsell P,
    4. Hedeland M,
    5. Bondesson U,
    6. Knutson L,
    7. Lennernäs H
    (2006) First-pass effects of verapamil on the intestinal absorption and liver disposition of fexofenadine in the porcine model. Drug Metab Dispos 34:1182–1189.
    OpenUrlAbstract/FREE Full Text
  24. ↵
    1. Perdaems N,
    2. Blasco H,
    3. Vinson C,
    4. Chenel M,
    5. Whalley S,
    6. Cazade F,
    7. Bouzom F
    (2010) Predictions of metabolic drug-drug interactions using physiologically based modelling: two cytochrome P450 3A4 substrates coadministered with ketoconazole or verapamil. Clin Pharmacokinet 49:239–258.
    OpenUrlCrossRefPubMed
  25. ↵
    1. Rittmaster RS,
    2. Stoner E,
    3. Thompson DL,
    4. Nance D,
    5. Lasseter KC
    (1989) Effect of MK-906, a specific 5α-reductase inhibitor, on serum androgens and androgen conjugates in normal men. J Androl 10:259–262.
    OpenUrlPubMed
  26. ↵
    1. Rowland Yeo K,
    2. Jamei M,
    3. Yang J,
    4. Tucker GT,
    5. Rostami-Hodjegan A
    (2010) Physiologically based mechanistic modelling to predict complex drug-drug interactions involving simultaneous competitive and time-dependent enzyme inhibition by parent compound and its metabolite in both liver and gut—the effect of diltiazem on the time-course of exposure to triazolam. Eur J Pharm Sci 39:298–309.
    OpenUrlCrossRefPubMed
  27. ↵
    1. Rubin GM,
    2. Tozer TN
    (1986) Hepatic binding and Michaelis-Menten metabolism of drugs. J Pharm Sci 75:660–663.
    OpenUrlCrossRefPubMed
  28. ↵
    1. Sakuma T,
    2. Shimojima T,
    3. Miwa K,
    4. Kamataki T
    (2004) Cloning CYP2D21 and CYP3A22 cDNAs from liver of miniature pigs. Drug Metab Dispos 32:376–378.
    OpenUrlAbstract/FREE Full Text
  29. ↵
    1. Sano N,
    2. Nio M,
    3. Ishii T,
    4. Amae S,
    5. Wada M,
    6. Nishi K,
    7. Endo N,
    8. Hayashi Y,
    9. Ohi R
    (2002) Oral FK 506 blood levels are elevated in pig short bowel model: further investigations with co-administration of an intestinal CYP3A4 inhibitor. Transplant Proc 34:1050–1051.
    OpenUrlCrossRefPubMed
  30. ↵
    1. Sjödin E,
    2. Fritsch H,
    3. Eriksson UG,
    4. Logren U,
    5. Nordgren A,
    6. Forsell P,
    7. Knutson L,
    8. Lennernäs H
    (2008) Intestinal and hepatobiliary transport of ximelagatran and its metabolites in pigs. Drug Metab Dispos 36:1519–1528.
    OpenUrlAbstract/FREE Full Text
  31. ↵
    1. Skaanild MT,
    2. Friis C
    (1997) Characterization of the P450 system in Gottingen minipigs. Pharmacol Toxicol 80 (Suppl 2):28–33.
    OpenUrlCrossRefPubMed
  32. ↵
    1. Steiner JF
    (1996) Clinical pharmacokinetics and pharmacodynamics of finasteride. Clin Pharmacokinet 30:16–27.
    OpenUrlPubMed
  33. ↵
    1. Sudduth SL,
    2. Koronkowski MJ
    (1993) Finasteride: the first 5 α-reductase inhibitor. Pharmacotherapy 13:309–329.
    OpenUrlPubMed
  34. ↵
    1. Suzuki R,
    2. Satoh H,
    3. Ohtani H,
    4. Hori S,
    5. Sawada Y
    (2010) Saturable binding of finasteride to steroid 5α-reductase as determinant of nonlinear pharmacokinetics. Drug Metab Pharmacokinet 25:208–213.
    OpenUrlCrossRefPubMed
  35. ↵
    1. Thompson IM,
    2. Goodman PJ,
    3. Tangen CM,
    4. Lucia MS,
    5. Miller GJ,
    6. Ford LG,
    7. Lieber MM,
    8. Cespedes RD,
    9. Atkins JN,
    10. Lippman SM,
    11. et al
    . (2003) The influence of finasteride on the development of prostate cancer. N Engl J Med 349:215–224.
    OpenUrlCrossRefPubMed
  36. ↵
    1. Thörn HA,
    2. Hedeland M,
    3. Bondesson U,
    4. Knutson L,
    5. Yasin M,
    6. Dickinson P,
    7. Lennernäs H
    (2009) Different effects of ketoconazole on the stereoselective first-pass metabolism of R/S-verapamil in the intestine and the liver: important for the mechanistic understanding of first-pass drug-drug interactions. Drug Metab Dispos 37:2186–2196.
    OpenUrlAbstract/FREE Full Text
  37. ↵
    1. Vertzoni MV,
    2. Reppas C,
    3. Archontaki HA
    (2006) Optimization and validation of a high-performance liquid chromatographic method with UV detection for the determination of ketoconazole in canine plasma. J Chromatogr B Analyt Technol Biomed Life Sci 839:62–67.
    OpenUrlCrossRefPubMed
  38. ↵
    1. Winchell GA,
    2. Gregoire S,
    3. Taylor AM,
    4. Hegland J,
    5. Hunninghake DB
    (1993) Finasteride, a steroid 5α-reductase inhibitor, does not affect the oxidative metabolism of antipyrine. J Clin Pharmacol 33:967–970.
    OpenUrlPubMed
  39. ↵
    1. Wong A,
    2. Bandiera SM
    (1998) Induction of hepatic cytochrome P450 2B and P450 3A isozymes in rats by zolazepam, a constituent of Telazol. Biochem Pharmacol 55:201–207.
    OpenUrlCrossRefPubMed
  40. ↵
    1. Wu CY,
    2. Benet LZ
    (2005) Predicting drug disposition via application of BCS: transport/absorption/ elimination interplay and development of a biopharmaceutics drug disposition classification system. Pharm Res 22:11–23.
    OpenUrlCrossRefPubMed
  41. ↵
    1. Yang J,
    2. Kjellsson M,
    3. Rostami-Hodjegan A,
    4. Tucker GT
    (2003) The effects of dose staggering on metabolic drug-drug interactions. Eur J Pharm Sci 20:223–232.
    OpenUrlCrossRefPubMed
  42. ↵
    1. Zhang X,
    2. Quinney SK,
    3. Gorski JC,
    4. Jones DR,
    5. Hall SD
    (2009) Semiphysiologically based pharmacokinetic models for the inhibition of midazolam clearance by diltiazem and its major metabolite. Drug Metab Dispos 37:1587–1597.
    OpenUrlAbstract/FREE Full Text
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In Vivo Investigation in Pigs of Intestinal Absorption, Hepatobiliary Disposition, and Metabolism of the 5α-Reductase Inhibitor Finasteride and the Effects of Coadministered Ketoconazole

Anna Lundahl, Mikael Hedeland, Ulf Bondesson and Hans Lennernäs
Drug Metabolism and Disposition May 1, 2011, 39 (5) 847-857; DOI: https://doi.org/10.1124/dmd.110.035311
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