Drug-drug interactions for UDP-glucuronosyltransferase substrates: a pharmacokinetic explanation for typically observed low exposure (AUCi/AUC) ratios.
Glucuronidation is a listed clearance mechanism for 1 in 10 of the top 200 prescribed drugs. The objective of this article is to encourage those studying ligand interactions with UDP-glucuronosyltransferases (UGTs) to adequately consider the potential consequences of in vitro UGT inhibition in humans. Spurred on by interest in developing potent and selective inhibitors for improved confidence around UGT reaction phenotyping, and the increased availability of recombinant forms of human UGTs, several recent studies have reported in vitro inhibition of UGT enzymes. In some cases, the observed potency of UGT inhibitors in vitro has been interpreted as having potential relevance in humans via pharmacokinetic drug-drug interactions. Although there are reported examples of clinically relevant drug-drug interactions for UGT substrates, exposure increases of the aglycone are rarely greater than 100% in the presence of an inhibitor relative to its absence (i.e., AUCi/AUC < or = 2). This small magnitude in change is in contrast to drugs primarily cleared by cytochrome P450 enzymes, where exposures have been reported to increase as much as 35-fold on coadministration with an inhibitor (e.g., ketoconazole inhibition of CYP3A4-catalyzed terfenadine metabolism). In this article the evidence for purported clinical relevance of potent in vitro inhibition of UGT enzymes will be assessed, taking the following into account: in vitro data on the enzymology of glucuronide formation from aglycone, pharmacokinetic principles based on empirical data for inhibition of metabolism, and clinical data on the pharmacokinetic drug-drug interactions of drugs primarily cleared by glucuronidation.
Williams
J Andrew
JA
Pharmacokinetics, Dynamics and Metabolism, Pfizer Global Research and Development, 2800 Plymouth Road, Ann Arbor, MI 48105, USA. james.williams2@pfizer.com.
Hyland
Ruth
R
Jones
Barry C
BC
Smith
Dennis A
DA
Hurst
Susan
S
Goosen
Theunis C
TC
Peterkin
Vincent
V
Koup
Jeffrey R
JR
Ball
Simon E
SE
D000818:Animals; D019540:Area Under Curve; D004347:Drug Interactions; D014453:Glucuronosyltransferase / Q000378:metabolism*; D006801:Humans; D004364:Pharmaceutical Preparations / Q000737:chemistry / Q000378:metabolism*; D013379:Substrate Specificity
D004364:Pharmaceutical Preparations; D014453:Glucuronosyltransferase