Cytochrome P450 3A4 messenger ribonucleic acid induction by rifampin in human peripheral blood mononuclear cells: Correlation with alprazolam pharmacokinetics

Objective There is significant interest in the assessment of the individual cytochrome P450 (CYP) 3A4 activity. We analyzed whether CYP3A4 messenger ribonucleic acid (mRNA) concentrations in leukocytes reflect CYP3A activity in the liver measured by alprazolam as an in vivo probe drug. We also wanted to identify whether genetically determined high CYP3A5 expression is associated with increased alprazolam clearance. Methods Alprazolam plasma concentrations were measured 10 hours after intake of 1 mg alprazolam. CYP3A4 mRNA concentrations in peripheral blood mononuclear cells were quantified in 96 healthy volunteers before and after 5-day treatment with 450 mg rifampin (INN, rifampicin) daily. Genetic polymorphisms in CYP2C19, CYP3A4, and CYP3A5 were analyzed by polymerase chain reaction, restriction fragment length polymorphism, and sequencing. Results The median alprazolam concentration measured 10 hours after dosage was 8.1 μg/L (range, 4.5-14.6 μg/L) before and 1.7 μg/L (range, 0.3-4.1 μg/L) after rifampin treatment. Leukocyte CYP3A4 mRNA was detectable in all samples with a median of 28 molecules per 1 ng total ribonucleic acid before (range, 10–128 molecules per 1 ng total ribonucleic acid) and 50 molecules per 1 ng total ribonucleic acid after (range, 9-484 molecules per 1 ng total ribonucleic acid) rifampin treatment (P < .001). However, mRNA concentrations before and during rifampin induction were largely overlapping, and there was a poor correlation between mRNA concentrations and alprazolam 10-hour trough concentrations reflecting CYP3A4 activity (r = −0.4, P < .001). Alprazolam kinetics did not differ between genetically determined expressers of CYP3A5 (genotype CYP3A5*1/*3) compared with homozygous carriers of the splice site variant. A marginally significant dependence of alprazolam concentrations from the CYP2C19 allele *2 was found (P = .04). Conclusions CYP3A4 mRNA concentrations in blood cells were very low and did not reflect systemic drug clearance mediated by CYP3A enzymes. The CYP3A5 genetic polymorphism does not appear relevant for alprazolam kinetics. Clinical Pharmacology & Therapeutics (2003) 74, 448–457; doi: 10.1016/S0009-9236(03)00237-6