RT Journal Article
SR Electronic
T1 Atorvastatin Glucuronidation Is Minimally and Nonselectively Inhibited by the Fibrates Gemfibrozil, Fenofibrate, and Fenofibric Acid
JF Drug Metabolism and Disposition
JO Drug Metab Dispos
FD American Society for Pharmacology and Experimental Therapeutics
SP 1315
OP 1324
DO 10.1124/dmd.107.015230
VO 35
IS 8
A1 Theunis C. Goosen
A1 Jonathan N. Bauman
A1 John A. Davis
A1 Chongwoo Yu
A1 Susan I. Hurst
A1 J. Andrew Williams
A1 Cho-Ming Loi
YR 2007
UL http://dmd.aspetjournals.org/content/35/8/1315.abstract
AB Gemfibrozil coadministration generally results in plasma statin area under the curve (AUC) increases, ranging from moderate (2- to 3-fold) with simvastatin, lovastatin, and pravastatin to most significant with cerivastatin (5.6-fold). Inhibition of statin glucuronidation has been postulated as a potential mechanism of interaction (Drug Metab Dispos 30:1280–1287, 2002). This study was conducted to determine the in vitro inhibitory potential of fibrates toward atorvastatin glucuronidation. [3H]Atorvastatin, atorvastatin, and atorvastatin lactone were incubated with human liver microsomes or human recombinant UDP-glucuronosyltransferases (UGTs) and characterized using liquid chromatography (LC)/tandem mass spectrometry and LC/UV/β-radioactivity monitor/mass spectrometry. [3H]Atorvastatin yields a minor ether glucuronide (G1) and a major acyl glucuronide (G2) with subsequent pH-dependent lactonization of G2 to yield atorvastatin lactone. Atorvastatin lactonization best fit substrate inhibition kinetics (Km = 12 μM, Vmax = 74 pmol/min/mg, Ki = 75 μM). Atorvastatin lactone yields a single ether glucuronide (G3). G3 formation best fit Michaelis-Menten kinetics (Km = 2.6 μM, Vmax = 10.6 pmol/min/mg). Six UGT enzymes contribute to atorvastatin glucuronidation with G2 and G3 formation catalyzed by UGTs 1A1, 1A3, 1A4, 1A8, and 2B7, whereas G1 formation was catalyzed by UGTs 1A3, 1A4, and 1A9. Gemfibrozil, fenofibrate, and fenofibric acid inhibited atorvastatin lactonization with IC50 values of 346, 320, and 291 μM, respectively. Based on unbound fibrate concentrations at the inlet to the liver, these data predict a small increase in atorvastatin AUC (∼1.2-fold) after gemfibrozil coadministration and no interaction with fenofibrate. This result is consistent with recent clinical reports indicating minimal atorvastatin AUC increases (∼1.2- to 1.4-fold) with gemfibrozil. The American Society for Pharmacology and Experimental Therapeutics