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Induction of CYP3A4 by Efavirenz in Primary Human Hepatocytes: Comparison With Rifampin and Phenobarbital

From the College of Pharmacy, University of Cincinnati Medical Center, Cincinnati, Ohio. S. C. Nallani's current affiliation is the Center for Drug Evaluation and Research, Food and Drug Administration, Rockville, Maryland.

The antiretroviral agent efavirenz enhances the systemic clearance of coadministered drugs that are cytochrome P450 (CYP) 3A4 substrates. The mechanism of the apparent increase in CYP3A4 activity by efavirenz and the magnitude of change relative to other known inducers are not known. The authors tested the hypothesis that increased enzymatic activity by efavirenz entails CYP3A4 induction and activation of the human pregnane X receptor (hPXR), a key transcriptional regulator of CYP3A4. Employing primary cultures of human hepatocytes, they compared the CYP3A4 inductive effects of efavirenz (1-10 µM) to rifampin (10 µM) and phenobarbital (2 mM). A cell-based reporter assay was employed to assess hPXR activation. The authors observed that efavirenz caused a concentration-dependent CYP3A4 induction and hPXR activation. Based on the CYP3A4 activity assay, the average magnitude of induction by efavirenz (5-10 µM) was approximately 3- to 4-fold. In comparison, phenobarbital (2 mM) and rifampin (10 µM) caused a 5- and 6-fold induction, respectively.

Key Words: CYP3A4 • enzyme induction • hepatocytes • hPXR • efavirenz • HIV • AIDS

Address for reprints: Pankaj B. Desai, College of Pharmacy, University of Cincinnati Medical Center, 3223 Eden Avenue, Mail Location #0004, Cincinnati, OH 45267.

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