Pharmacokinetic Effect of AMD070, an Oral CXCR4 Antagonist, on CYP3A4 and CYP2D6 Substrates Midazolam and Dextromethorphan in Healthy Volunteers

BACKGROUND:Many antiretroviral drugs used in HIV care involve complex drug metabolism by CYP3A4 and CYP2D6 enzymes, and drug interactions are problematic clinically. AMD070, a novel entry inhibitor, is an inhibitor of X4-tropic HIV virus. In vitro data suggested that it is a CYP3A4 substrate and may inhibit CYP2D6 and CYP3A4. METHODS:Twelve healthy subjects were given a single oral dose of 5 mg of midazolam and 30 mg of dextromethorphan on day 1 and 9, and 200 mg of AMD070 twice daily on days 2 through 9 (inclusive). Pharmacokinetic parameters of midazolam and dextromethorphan were assessed alone and in the presence of AMD070. RESULTS:The mean AUC0-24 and Cmax of dextromethorphan increased 2.86-fold (2.20 to 5.10, 90% confidence interval [CI]) and 2.52-fold (1.99 to 4.24, 90% CI), respectively, in the presence of AMD070. Plasma AUC0-12 of midazolam increased 1.33-fold (1.15 to 1.61, 90% CI) without change in Cmax. The half-life did not change for both drugs, but significant, parallel decrease in apparent oral clearance and volume of distribution was observed. CONCLUSIONS:The data support an alteration in bioavailability due to an AMD070-mediated inhibition of presystemic metabolism, though an intestinal P-glycoprotein effect could also be contributing. Interactions between AMD070 with CYP3A4 and, especially, 2D6 substrates of clinical importance in HIV care should be further explored.