On 6 January the FDA approved revisions to the efavirenz (Sustiva) package insert to include dosing with efavirenz and rifampin. The Dosage and Administration and Drug Interaction sections of the package insert were updated to include the following:
If Sustiva is coadministered with rifampin to patients weighing 50 kg or more, an increase in the dose of Sustiva to 800 mg once daily is recommended.
The recommendation to increase the dose of efavirenz to 800 mg in patients weighing 50 kg or more when efavirenz is co-administered with rifampin is based on empirical data from two drug-drug interaction trials (one trial in healthy volunteers and one trial in HIV-1 infected patients) and semi-mechanistic population pharmacokinetic modeling. The population pharmacokinetic model was constructed using data collected in the drug-drug interaction trials and single-and multiple dose pharmacokinetic data of efavirenz from other healthy volunteer trials.
The data from the drug-drug interaction trials showed that rifampin decreased the exposure of efavirenz 600 mg once daily. Further, the systemic exposure of efavirenz, when efavirenz 800 mg was coadministered with rifampin, was similar to the systemic exposure of efavirenz when efavirenz 600 mg once daily was given alone. The results from the population pharmacokinetic analysis were consistent with the empirical data.
Source: FDA HIV/AIDS Update (06 January 2012).
For full details please refer to the updated prescribing information:
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