Dicloxacillin induces CYP2C19, CYP2C9 and CYP3A4 in vivo and in vitro.

Abstract

The aim of this study was to study potential cytochrome P450 (CYP) induction by dicloxacillin. We performed an open-label, randomized, two-phase, five-drug clinical pharmacokinetic cocktail crossover study in 12 healthy men with and without pretreatment with 1g dicloxacillin three times daily for 10days. Plasma and urine were collected over 24h and the concentration of all five drugs and their primary metabolites was determined using a liquid chromatography coupled to triple quadrupole mass spectrometry method. Cryopreserved primary human hepatocytes were exposed to dicloxacillin for 48h and changes in gene expression and the activity of CYP3A4, CYP2C9, CYP2B6 and CYP1A2 were investigated. The activation of nuclear receptors by dicloxacillin was assessed using luciferase assays. A total of 10days of treatment with dicloxacillin resulted in a clinically and statistically significant reduction in the area under the plasma concentration-time curve from 0 to 24h for omeprazole (CYP2C19) {geometric mean ratio [GMR] [95% confidence interval (CI)]: 0.33 [0.24, 0.45]}, tolbutamide (CYP2C9) [GMR (95% CI): 0.73 (0.65, 0.81)] and midazolam (CYP3A4) [GMR (95% CI): 0.54 (0.41, 0.72)]. Additionally, other relevant pharmacokinetic parameters were affected, indicating the induction of CYP2C- and CYP3A4-mediated metabolism by dicloxacillin. Investigations in primary hepatocytes showed a statistically significant dose-dependent increase in CYP expression and activity by dicloxacillin, caused by activation of the pregnane X receptor. Dicloxacillin is an inducer of CYP2C- and CYP3A-mediated drug metabolism, and we recommend caution when prescribing dicloxacillin to users of drugs with a narrow therapeutic window.