Drug Interactions between atazanavir and famotidine

ADJUST DOSE: Concurrent administration of H2-receptor antagonists may decrease the oral bioavailability of atazanavir and substantially reduce its concentrations in plasma. Atazanavir solubility decreases with increasing pH, thus inhibition of gastric acid secretion may interfere with dissolution of the drug. Subtherapeutic antiretroviral drug levels may lead to reduced viral susceptibility and development of resistance.

ADJUST DOSE: Concurrent administration of atazanavir/cobicistat or atazanavir/ritonavir with tenofovir and H2-receptor antagonists may decrease the oral bioavailability of atazanavir by an additional 10% to 20%, compared to concurrent use with an H2 antagonist alone.

MANAGEMENT: When used with atazanavir/cobicistat or atazanavir/ritonavir once daily in adults, the dosage of the H2-receptor antagonist should be no more than the equivalent of famotidine 40 mg twice daily in antiretroviral treatment-naive patients and 20 mg twice daily in treatment-experienced patients. Atazanavir/cobicistat or atazanavir/ritonavir should be administered simultaneously with, and/or at least 10 hours after, the H2-receptor antagonist. If tenofovir is also prescribed, no additional precaution is necessary in treatment-naive patients, whereas the dosage of atazanavir/ritonavir should be increased to 400 mg/100 mg once a day in treatment-experienced patients. All three antiretroviral agents should be administered as a single daily dose with food. In the event that ritonavir is not tolerated by a treatment-naive patient, atazanavir may be administered at an increased dosage of 400 mg once daily at least 2 hours before and at least 10 hours after the H2-receptor antagonist. Dosage of the H2-receptor antagonist should not exceed the equivalent of famotidine 20 mg twice daily. Atazanavir without ritonavir is not recommended for treatment-experienced patients with prior virologic failure or pregnant women. For treatment-experienced pregnant women during the second or third trimester, when atazanavir is coadministered with either an H2-receptor antagonist or tenofovir, atazanavir 400 mg with ritonavir 100 mg once daily is recommended. There are insufficient data to recommend an atazanavir dosage for use with both an H2-receptor antagonist and tenofovir in treatment-experienced pregnant women. No dosage adjustment is required for postpartum patients. However, patients should be closely monitored for adverse events because atazanavir exposures could be higher during the first 2 months after delivery. Coadministration of atazanavir/cobicistat in combination with tenofovir and an H2 receptor antagonist should generally be avoided. There are insufficient data to recommend an atazanavir/cobicistat dosage for use with both an H2-receptor antagonist and tenofovir.

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