The nature and extent of drug-drug interactions between oral drugs is affected by numerous modulators. The effect of the formulation (prolonged release (PR) vs. immediate release (IR)) of a victim drug during treatment with a CYP3A (cytochrome P450 enzyme 3A4) inhibitor is unknown but expected to be smaller with PR. We studied PR and IR tacrolimus during treatment with the strong CYP3A inhibitor voriconazole in 18 healthy volunteers in a pharmacokinetic, four-phase, crossover trial. The exposure increase was significantly smaller after PR tacrolimus than after IR tacrolimus (AUC (area under the curve) 2.62-fold vs. 6.02-fold, P < 0.001; Cmax (maximum concentration) 2.02-fold vs. 2.7-fold, P = 0.026) and less variable (AUC increase 1.6 to 4.8-fold vs. 1.8 to 19-fold). CYP3A5 genotype, voriconazole exposure, and CYP3A4 phenotype (determined with a midazolam microdose) were not related to the relative change in tacrolimus exposure. Thus, when considering drug-drug interactions with CYP3A inhibitors, the formulation of orally administered victim drugs should also be considered.
© 2019 The Authors Clinical Pharmacology & Therapeutics © 2019 American Society for Clinical Pharmacology and Therapeutics.