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U.S. Department of Health and Human Services


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Doral (quazepam) oral tablets

Detailed View: Safety Labeling Changes Approved By FDA Center for Drug Evaluation and Research (CDER) -- September 2009


Summary View



Drug Interactions
  • Quazepam is a mechanism based inhibitor of CYP2B6 based on an in vitro study. However, the in vivo extrapolation of this is unknown. It may be possible that co-administration of Doral and drugs primarily metabolized by CYP2B6 (e.g., efavirenz and bupropion) may result in increased plasma concentrations of these drugs resulting in an increase in adverse events (e.g., CNS toxicities associated with efavirenz and precipitation of seizures with bupropion). Patients taking medications that are CYP2B6 substrates with Doral should be monitored closely for adverse reactions associated with these medications. If adverse events are observed, clinicians may consider the discontinuation of Doral and the selection of an alternative anxiolytic agent.


Drug-Drug Interactions
  • In vitro inhibition studies conducted to assess the potential of quazepam to inhibit CYP2B6, CYP2C8 and CYP2E1 at relevant clinical Cmax concentrations (0.15 μM = 58 ng/mL) demonstrate quazepam is a CYP2B6 mechanism based inhibitor. Increased plasma concentrations of drugs that are substrates of CYP2B6 may result if coadministered with Doral.