Ethanol: Ethanol decreases the elimination of abacavir, causing an increase in overall exposure. Dosage adjustments are not needed.
Interferon alfa: Hepatic decompensation (some fatal) has occurred in HIV/Hepatitis C virus (HCV) coinfected patients receiving antiretroviral therapy for HIV-1 and interferon alfa, with or without ribavirin. Closely monitor patients for treatment-associated toxicities during coadministration.
Methadone: Methadone clearance increased 22% during coadministration. In the majority of patients, this alteration will not result in a methadone dose modification. In addition, methadone may delay the absorption of abacavir/lamivudine, resulting in a decrease in bioavailability.
Nelfinavir: Single-dose administration lamivudine 150 mg after pretreatment with nelfinavir 750 mg every 8 hours for 7-10 days increased the lamivudine AUC 10%. Dosage adjustments are not needed.
Ribavirin: Ribavirin may reduce the phosphorylation of lamivudine.
Trimethoprim/Sulfamethoxazole: Coadministration of lamivudine with trimethoprim 160 mg/sulfamethoxazole 800 mg increased lamivudine AUC 43%. Dosage adjustments are not needed.