What the FDA labels say about taking them together
Efavirenz and fosamprenavir
Efavirenz's FDA label of March 31, 2024 names fosamprenavir in its drug interactions section, and fosamprenavir's label names efavirenz too. The efavirenz label: “Fosamprenavir (unboosted): Appropriate doses of the combinations with respect to safety and efficacy have not been established. Fosamprenavir/ritonavir: An additional 100 mg/day (300 mg total) of ritonavir is …”
Check it at the source: the efavirenz FDA label on DailyMed (effective March 31, 2024, Cipla USA Inc.); the fosamprenavir FDA label on DailyMed (effective September 15, 2023, Mylan Pharmaceuticals Inc.).
What does the efavirenz label say about fosamprenavir?
Efavirenz label, drug interactionsConcomitant Drug Class/Drug Name: Protease inhibitor: Fosamprenavir Calcium; Effect: ↓ amprenavir; Clinical Comment: Fosamprenavir (unboosted): Appropriate doses of the combinations with respect to safety and efficacy have not been established. Fosamprenavir/ritonavir: An additional 100 mg/day (300 mg total) of ritonavir is recommended when efavirenz is administered with fosamprenavir/ritonavir once daily. No change in the ritonavir dose is required when efavirenz is administered with fosamprenavir plus ritonavir twice daily.
Source: FDA drug label (Efavirenz), Cipla USA Inc., effective March 31, 2024 (SPL set 92603fa5-7a2c-4bfb-9a70-aadb4fba952c), via openFDA; the full label on DailyMed
What does the fosamprenavir label say about efavirenz?
Fosamprenavir label, drug interactionsConcomitant Drug Class/Drug Name: Non-nucleoside reverse transcriptase inhibitor: Efavirenz; Effect on Concentration of Amprenavir or Concomitant Drug: Fosamprenavir: ↓ Amprenavir; Clinical Comment: Appropriate doses of the combinations with respect to safety and efficacy have not been established.
Source: FDA drug label (Fosamprenavir Calcium), Mylan Pharmaceuticals Inc., effective September 15, 2023 (SPL set 3a1424d8-844c-4e24-9ebd-b2c2b61b61a3), via openFDA; the full label on DailyMed
These are the labels' own sentences. PlainMeds does not grade interactions; a pharmacist or prescriber can say what they mean for one person's medicines.
Both medicines on the record
| Efavirenz | Fosamprenavir | |
|---|---|---|
| Labeled for | HIV | HIV |
| Boxed warning | No | No |
| Pharmacy cost (NADAC) | $1.28 per tablet 600 mg tablet | n/a |
| Shortage now | No current entry | No current entry |
Source: FDA NDC Directory, CMS NADAC of October 7, 2026 and the FDA Drug Shortage Database (FDA files October 8, 2026)
What next?
- Check more medicines together
- up to five at once