@article {Tian724, author = {Dan-Dan Tian and Cathrine Leonowens and Emily J. Cox and Vanessa Gonz{\'a}lez-P{\'e}rez and Kosea S. Frederick and Yolanda V. Scarlett and Michael B. Fisher and Mary F. Paine}, title = {Indinavir Increases Midazolam N-Glucuronidation in Humans: Identification of an Alternate CYP3A Inhibitor Using an In Vitro to In Vivo Approach}, volume = {47}, number = {7}, pages = {724--731}, year = {2019}, doi = {10.1124/dmd.119.087007}, publisher = {American Society for Pharmacology and Experimental Therapeutics}, abstract = {Midazolam is a widely used index substrate for assessing effects of xenobiotics on CYP3A activity. A previous study involving human hepatocytes showed the primary route of midazolam metabolism, 1'-hydroxylation, shifted to N-glucuronidation in the presence of the CYP3A inhibitor ketoconazole, which may lead to an overprediction of the magnitude of a xenobiotic{\textendash}midazolam interaction. Because ketoconazole is no longer recommended as a clinical CYP3A inhibitor, indinavir was selected as an alternate CYP3A inhibitor to evaluate the contribution of the N-glucuronidation pathway to midazolam metabolism. The effects of indinavir on midazolam 1'-hydroxylation and N-glucuronidation were first characterized in human-derived in vitro systems. Compared with vehicle, indinavir (10 μM) inhibited midazolam 1'-hydroxylation by recombinant CYP3A4, human liver microsomes, and high-CYP3A activity cryopreserved human hepatocytes by >=70\%; the IC50 obtained with hepatocytes (2.7 μM) was within reported human unbound indinavir Cmax (<=5 μM). Midazolam N-glucuronidation in hepatocytes increased in the presence of indinavir in both a concentration-dependent (1{\textendash}33 μM) and time-dependent (0{\textendash}4 hours) manner (by up to 2.5-fold), prompting assessment in human volunteers (n = 8). As predicted by these in vitro data, indinavir was a strong inhibitor of the 1'-hydroxylation pathway, decreasing the 1'-hydroxymidazolam/midazolam area under the plasma concentration versus time curve (AUC)0{\textendash}12h ratio by 80\%. Although not statistically significant, the midazolam N-glucuronide/midazolam AUC0{\textendash}12h ratio increased by 40\%, suggesting a shift to the N-glucuronidation pathway. The amount of midazolam N-glucuronide recovered in urine increased 4-fold but remained \<10\% of the oral midazolam dose (2.5 mg). A powered clinical study would clarify whether N-glucuronidation should be considered when assessing the magnitude of a xenobiotic{\textendash}midazolam interaction.}, issn = {0090-9556}, URL = {https://dmd.aspetjournals.org/content/47/7/724}, eprint = {https://dmd.aspetjournals.org/content/47/7/724.full.pdf}, journal = {Drug Metabolism and Disposition} }