Drug interactions
Efavirenz + Nirmatrelvir / ritonavir
Severity: Moderate
Efavirenz and Nirmatrelvir / ritonavir: moderate interaction.
Last updated
For healthcare professionals — reference only. This page is a brief summary, not medical advice and not a substitute for official labeling or clinical judgement. Always verify before prescribing or dispensing.
Summary
Efavirenz is a CYP3A4 inducer and may lower concentrations of nirmatrelvir and ritonavir, potentially reducing antiviral efficacy against COVID-19. Ritonavir inhibits CYP3A4, but efavirenz clearance depends mainly on CYP2B6, so large changes in efavirenz levels are not expected. Patients on efavirenz-based HIV therapy need review of the whole regimen.
What this interaction means in plain words
Efavirenz and Nirmatrelvir / ritonavir can affect each other. The combination is often manageable, but it may need a change of dose, a change of timing, or extra checks while both are taken.
Why it happens
Efavirenz induces CYP3A4 and may reduce nirmatrelvir and ritonavir exposure, while ritonavir inhibition has a limited effect on efavirenz.
What to do
Co-administration is possible with monitoring. Watch for efavirenz adverse effects such as CNS symptoms and for COVID-19 treatment response, and review with an HIV specialist.
What to ask your pharmacist
- Should I take them at different times of day?
- Does the dose of either medicine need to change?
- Is there anything I should avoid, such as alcohol or certain foods, while on both?
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Other interactions of Efavirenz
- Cobimetinib + Efavirenz Contraindicated
- Dienogest / estradiol valerate + Efavirenz Contraindicated
- Dihydroergotamine intranasal + Efavirenz Contraindicated
- Dihydroergotamine + Efavirenz Contraindicated
- Doravirine + Efavirenz Contraindicated
- Efavirenz + Elbasvir / grazoprevir Contraindicated
Frequently asked questions
Can I take Efavirenz with Nirmatrelvir / ritonavir?
MediHelp rates the interaction as moderate. Efavirenz and Nirmatrelvir / ritonavir can affect each other. The combination is often manageable, but it may need a change of dose, a change of timing, or extra checks while both are taken. Efavirenz is a CYP3A4 inducer and may lower concentrations of nirmatrelvir and ritonavir, potentially reducing antiviral efficacy against COVID-19. Ritonavir inhibits CYP3A4, but efavirenz clearance depends mainly on CYP2B6, so large changes in efavirenz levels are not expected. Patients on efavirenz-based HIV therapy need review of the whole regimen.
How serious is the interaction between Efavirenz and Nirmatrelvir / ritonavir?
MediHelp rates it moderate, on a four-level scale (minor, moderate, major, contraindicated) based on published labels and references. What to do, in brief: Co-administration is possible with monitoring. Watch for efavirenz adverse effects such as CNS symptoms and for COVID-19 treatment response, and review with an HIV specialist.
What other medicines interact with Efavirenz?
MediHelp also lists interactions of Efavirenz with, for example, Cobimetinib, Dienogest / estradiol valerate, Dihydroergotamine intranasal. The full list is on the Efavirenz page.
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