Fosamprenavir and Nirmatrelvir and ritonavir interaction
Fosamprenavir and Nirmatrelvir and ritonavir: 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 Fosamprenavir (Fosamprenavir Calcium) label · effective 2026-06-30
The list of contraindicated drugs applies to the use of fosamprenavir calcium with or without ritonavir, unless otherwise indicated.
If fosamprenavir calcium is coadministered with ritonavir, reference should be made to the full prescribing information for ritonavir for additional contraindications.
Fosamprenavir calcium is contraindicated when coadministered with the following drugs: Alpha 1-adrenoreceptor antagonist: Alfuzosin Antiarrhythmics: Flecainide (with ritonavir ), propafenone (with ritonavir ) Antimycobacterial: Rifampin Antipsychotic: Lurasidone (with ritonavir ), pimozide Ergot derivatives: Dihydroergotamine, ergonovine, ergotamine, methylergonovine…
Review ritonavir contraindications when used in combination.
…clinically significant adverse reactions, potentially leading to severe, life-threatening, or fatal events from greater exposures of concomitant medications. clinically significant adverse reactions from greater exposures of fosamprenavir calcium/ritonavir. loss of therapeutic effect of fosamprenavir calcium/ritonavir and possible development of resistance.
From the Nirmatrelvir and ritonavir (Paxlovid) label · effective 2026-02-19
• HIV-1 Drug Resistance: PAXLOVID use may lead to a risk of HIV-1 developing resistance to HIV protease inhibitors in individuals with uncontrolled or undiagnosed HIV-1 infection.
Risk of HIV-1 Resistance Development Because nirmatrelvir is co-administered with ritonavir, there may be a risk of HIV-1 developing resistance to HIV protease inhibitors in individuals with uncontrolled or undiagnosed HIV-1 infection [see Contraindications (4) and Drug Interactions (7) ] .
Monitor for increased PAXLOVID or protease inhibitor adverse events .
Anti-HIV protease inhibitors atazanavir, darunavir, tipranavir ↑ protease inhibitor For further information, refer to the respective protease inhibitors' prescribing information.
Anti-HIV efavirenz, maraviroc, nevirapine, zidovudine, bictegravir/ emtricitabine/ tenofovir ↑ efavirenz ↑ maraviroc ↑ nevirapine ↓ zidovudine ↑ bictegravir ↔ emtricitabine ↑ tenofovir For further information, refer to the respective anti-HIV drugs prescribing information.
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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.