ArticlesEnterohepatic Recirculation and Renal Metabolism of Morphine in the Rat
Abstract
Morphine (2.5 mg/kg) was administered iv to intact (I), bile duct-cannulated (BC), and bile duct-cannulated–renal-ligated (BC–RL) rats (n = 4 per group) to investigate the extent of enterohepatic recirculation and renal metabolism of the drug. A decrease in the serum area under the concentration–time curve (AUC) was observed for the BC in comparison with I rats. From these AUC values, it was determined that ~16% of the administered dose was subject to enterohepatic recirculation. In addition, a statistically significant (p < 0.05) decrease in the systemic clearance of morphine was observed in the BC–RL rats compared with the BC animals (55.2 ± 17.2 versus 31.4 ± 8.5 mL/min/kg). This decrement in systemic clearance appeared to be the result of a significant decrease in the formation clearance of morphine glucuronide after ligation of the renal pedicles (23.2 ± 4.8 versus 10.9 ± 5.0 mL/min/kg). Renal metabolic clearance was calculated as 15.7 mL/min/kg, accounting for 28.5% of the systemic clearance of morphine. Hepatic clearance (31.4 ± 8.5 mL/min/kg) accounted for 56.8% of total systemic clearance.
References (0)
Cited by (29)
High-performance liquid chromatographic assay for morphine in small plasma samples: Application to pharmacokinetic studies in rats
2006, Journal of Pharmaceutical and Biomedical AnalysisIn order to perform a reliable pharmacokinetic study of morphine during subchronic treatment in rats, an easy, rapid, sensitive and selective analytical method was proposed and validated. The analyte and internal standard (naloxone) were extracted from plasma samples (100 μL) by a single solid-phase extraction method prior to reverse-phase high performance liquid chromatography (HPLC) along with electrochemical detection (ED). Standard calibration graphs were linear within a range of 3.5–1000 ng/mL (r = 0.999). The intra-day coefficients of variation (CV) were in the range of 5.8–8.5% at eight concentration levels (7–1000 ng/mL) and the inter-day coefficient of variation ranged from 7.4 to 8.8%. The intra-day assay accuracy was in the range of −5–10% and the inter-day assay accuracy ranged from 3.0 to 9.3% of relative error (RE). The limit of quantification was 3.5 ng/mL using a plasma sample of 100 μL (15.8% of CV and 12.8% of RE). Plasma samples were stable for 2 months at −20 °C. This method was found to be suitable for pharmacokinetic studies in rats, after subcutaneous administration of morphine (5.6 mg/kg per day) in subchronic treatment for 6 and 12 days.
Absorption and enterohepatic circulation of baicalin in rats
2005, Life SciencesPharmacokinetics of baicalin, in form of its parent drug (BG) and conjugated metabolites (BGM), were studied following intravenous and oral administration of baicalin to intact rats. The enterohepatic circulation of BG and BGM was also assessed in a linked-rat model. Multiple plasma and urine samples were collected, and concentrations of BG and BGM were determined using a liquid chromatography/tandem mass spectrometry method. The concentration of BGM was assayed in the form of baicalein after treatment with β-glucuronidase/sulfatase. After i.v. administration, plasma concentration of BG rapidly declined with the elimination half-life (T1 / 2) of 0.1 till 4 h post dose, followed by slight increase from 4–8 h in plasma concentrations after drug administration. These plasma concentrations resulted in a significant prolongation of the terminal elimination half-life of BG (T1 / 2 TER, 9.7 h). BG also displayed slight increase in plasma concentrations (12–24 h) after oral administration, with T1 / 2 TER of 12.1 h. Based on the AUC of BG and BGM, the absolute bioavailability of baicalin was 2.2 ± 0.2% and 27.8 ± 5.6%, respectively. The exposure of baicalin to the systemic circulation was approximately 118-fold lower than that of BGM after oral administration (AUC0−t, 4.43 versus 523.97 nmol·h/mL). The high extent of glucuronidation suggested the possible presence of enterohepatic circulation, which was confirmed in the linked-rat model since plasma concentrations of BG and BGM were observed in bile-recipient rats at 4 to 36 h. The extent of enterohepatic circulation after intravenous administration of baicalin was 4.8% and 13.3% for BG and BGM, respectively. It was determined that 18.7% and 19.3% of the administered baicalin were subjected to enterohepatic circulation for BG and BGM, respectively, after oral administration. These results confirm that BG undergoes extensive first-pass glucuronidation and that enterohepatic circulation contributes significantly to the exposure of BG and BGM in rats.
Uncertainty factors for chemical risk assessment: Interspecies differences in glucuronidation
2001, Food and Chemical ToxicologyFor the risk assessment of effects other than cancer, a safe daily intake in humans is generally derived from a surrogate threshold dose (e.g. NOAEL) in an animal species to which an uncertainty factor of 100 is usually applied. This 100-fold is to allow for possible interspecies (10-fold) and interindividual (10-fold) differences in response to a toxicant, and incorporates toxicodynamic and toxicokinetic aspects of variability. The current study determined the magnitude of the interspecies differences in the internal dose of compounds for which glucuronidation is the major pathway of metabolism in either humans or in the test species. The results showed that there are major interspecies differences in the nature of the biological processes which influence the internal dose, including the route of metabolism, the extent of presystemic metabolism and enterohepatic recirculation. The work presented does not support the refinement of the interspecies toxicokinetic default to species- and pathway-specific values, but demonstrates the necessity for risk assessments to be carried out using quantitative chemical-specific data which define the fundamental processes which will influence the internal dose of a chemical (toxicokinetics), or the interaction of toxicant with its target site (toxicodynamics).
Limited phase I study of morphine-3-glucuronide
2001, Journal of Pharmaceutical SciencesCitation Excerpt :This, they concluded, represented the effect of biliary excretion, and, as it was more pronounced after oral morphine, evidence for enterohepatic cycling. Biliary excretion of M3G has been demonstrated in rats,26 and there is some evidence for such a phenomena in humans.27 However, the relative contribution of this route of elimination appears to be small with perhaps high concentrations, but relatively small amounts of the glucuronides eliminated in bile.
The toxicity of morphine-3-glucuronide (M3G) has been investigated in an open, uncontrolled, single-blinded, single dose study over a limited range of doses. Three cohorts each of three healthy volunteers received 7.5, 15, and 30 mg/70 kg intravenous (IV) M3G. Blood sampling was undertaken for the following 24 h. Subjective toxicity was recorded on visual analogue scales and plasma M3G concentrations measured by a specific HPLC assay. Virtually no effects and no change in cardiovascular or respiratory parameters were seen. The pharmacokinetics fitted a two-compartment model. The mean elimination half-life (± S.D.) of M3G was 1.66 (± 0.47) h. Mean AUC standardized to a dose of 1 mg/70 kg was 228 (± 62) ηmolL−1 · h. Mean M3G clearance was 169 (± 48) mLmin−1 and the mean volume of distribution was 23.1 (± 4.8) liters. At the doses investigated there were no clear neuroexcitatory effects, no opioid effects, and the pharmacokinetics were very similar to those of morphine-6-glucuronide (M6G). © 2001 Wiley-Liss, Inc. and the American Pharmaceutical Association J Pharm Sci 90:1810–1816, 2001
The aims of this study were to examine the effect of old age on the pharmacokinetics of morphine and morphine-6β-glucuronide (M6G) and their relationships to antinociceptive activity. Morphine (21.0 μmol/kg) or M6G (21.7 μmol/kg) were administered s.c. to young adult and aged male Hooded-Wistar rats. Antinociceptive effect was measured by the tail-flick method at various times up to 2.5 h or 6.5 h after morphine or M6G administration, respectively, and concentrations of morphine, morphine-3β-glucuronide (M3G) and M6G in plasma and brain were determined by HPLC. Creatinine clearance was significantly lower by 33% or 21% in aged compared to young adult rats receiving morphine or M6G, respectively. After morphine administration, the areas under the (i) antinociceptive effect-time curve, (ii) plasma morphine concentration-time curve, and (iii) brain morphine concentration-time curve were not different between young adult and aged rats. However, the AUC for plasma M3G was five-fold higher in the aged relative to young adult rats, which could not be accounted for by only a 33% lower creatinine clearance. M6G was not detected in any plasma or brain sample from rats administered morphine and no M3G was detected in brain. For M6G administration, the areas under the (i) antinociceptive effect-time curve, and (ii) plasma M6G concentration-time curve were 1.8- and 1.6-fold higher in aged compared to young adult rats, respectively. Concentrations of M6G in brain were below the limit of quantification. No morphine or M3G was detected in any of the plasma or brain samples of rats administered M6G. The results demonstrate no change in morphine antinociception and pharmacokinetics with age, and suggest that blood-brain barrier permeability and receptor sensitivity to morphine are not altered in aged rats. Accumulation of M3G in plasma of aged rats is probably due to diminished renal clearance of M3G in addition to a reduction in the biliary excretion of M3G. The heightened sensitivity of the aged rats to M6G is probably due to the observed altered kinetics of M6G rather than a pharmacodynamic change.
Effect of prior morphine-3-glucuronide exposure on morphine disposition and antinociception
1997, Biochemical PharmacologyMorphine-3-glucuronide (M3G), the primary metabolite of morphine in humans and rats, has been reported to antagonize morphine-induced pharmacologic effects. The present experiment was conducted to evaluate the effect of prior systemic M3G exposure on morphine disposition and antinociceptive response in male Sprague-Dawley rats. Saline (N = 6), low dose M3G (0.15 mg/hr, N = 7), or high dose M3G (0.30 mg/hr, N =6) was infused for 720 min prior to the administration of morphine by i.v. bolus (2 mg/kg). Tail-flick latencies in response to hot water (50°) were assessed prior to and for 180 min after the morphine test dose. M3G exposure had no significant effect on morphine pharmacokinetics, although a disproportionate increase in M3G concentrations was observed following the morphine i.v. bolus dose in rats infused with high dose M3G. Morphine-induced antinociception, expressed as the percent of maximum response (%MPR), was maximum 15 min after morphine administration and returned to baseline by 180 min. A pharmacokinetic-pharmacodynamic model was constructed to relate tail-flick latencies to morphine serum concentrations. In saline-exposed rats, the antinociceptive response to morphine was characterized by a sigmoidal Emax model, with an ec50 of 328 ng/mL, a Hill coefficient (γ) of 4.5, and a half-life for the offset of pharmacologic effect of 11 min. No statistically significant differences in the intensity or duration of morphine-induced response were detected between salineand M3G-exposed animals. These results suggest that systemic formation of M3G is unlikely to contribute significantly to the development of tolerance to morphine antinociception.