Efavirenz, lamivudine, and tenofovir and Fosamprenavir interaction
Efavirenz, lamivudine, and tenofovir and Fosamprenavir: both prescribing labels flag this combination with the strongest language, such as a contraindication, a boxed warning, or an instruction to avoid it.
Do not combine without a prescriber's guidance. The label language below is the strongest FDA uses.
What the FDA labels say
From the Efavirenz, lamivudine, and tenofovir (SYMFI) label · effective 2019-10-15
Lactic Acidosis and Severe Hepatomegaly with Steatosis Lactic acidosis and severe hepatomegaly with steatosis, including fatal cases, have been reported with the use of nucleoside analogs and other antiretrovirals.
• SYMFI should not be administered with other antiretroviral medications for the treatment of HIV-1 infection.
Not Recommended with Other Antiretroviral Medications SYMFI is a complete regimen for the treatment of HIV-1 infection; therefore, it should not be administered with other antiretroviral medications for treatment of HIV-1 infection.
From the Fosamprenavir (Fosamprenavir Calcium) label · effective 2026-06-30
Fosamprenavir calcium/ritonavir: ↑ Amprenavir ↓Delavirdine Non-nucleoside reverse transcriptase inhibitor: Efavirenz a Fosamprenavir calcium: ↓ Amprenavir Fosamprenavir calcium/ritonavir: ↓ Amprenavir Appropriate doses of the combinations with respect to safety and efficacy have not been established.
No change in the ritonavir dose is required when efavirenz is administered with Fosamprenavir calcium plus ritonavir twice daily.
Initiation of medications that inhibit or induce CYP3A may increase or decrease concentrations of fosamprenavir calcium/ritonavir, respectively.
Coadministration of fosamprenavir calcium with drugs that induce CYP3A4 may decrease amprenavir (active metabolite) concentrations leading to potential loss of virologic activity.
Coadministration of fosamprenavir calcium and drugs that induce CYP3A4, such as rifampin, may decrease amprenavir concentrations and reduce its therapeutic effect.
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Open in the checkerNot medical advice. Interaction Checker quotes FDA label text and NIH fact sheets. Whether an interaction matters for you depends on doses, timing, kidney and liver function, and other conditions. Confirm with a pharmacist or prescriber.