What the FDA labels say about taking them together
Fosamprenavir and rifabutin
Fosamprenavir's FDA label of September 15, 2023 names rifabutin in its drug interactions section, and rifabutin's label names fosamprenavir too. The rifabutin label: “Reduce rifabutin dose by at least 75% when given with fosamprenavir/ritonavir combination.”
Check it at the source: the fosamprenavir FDA label on DailyMed (effective September 15, 2023, Mylan Pharmaceuticals Inc.); the rifabutin FDA label on DailyMed (effective September 1, 2026, REMEDYREPACK INC.).
What does the fosamprenavir label say about rifabutin?
Fosamprenavir label, drug interactionsConcomitant Drug Class/Drug Name: Antimycobacterial: Rifabutin; Effect on Concentration of Amprenavir or Concomitant Drug: ↑ Rifabutin and rifabutin metabolite; Clinical Comment: A complete blood count should be performed weekly and as clinically indicated to monitor for neutropenia. Fosamprenavir: A dosage reduction of rifabutin by at least half the recommended dose is required. Fosamprenavir/ritonavir: Dosage reduction of rifabutin by at least 75% of the usual dose of 300 mg/day is recommended (a maximum dose of 150 mg every other day or 3 times per week).
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
What does the rifabutin label say about fosamprenavir?
Rifabutin label, drug interactionsCo-administered drug: Fosamprenavir/ritonavir; Dosing regimen of co-administered drug: 700 mg twice a day plus ritonavir 100 mg twice a day for 2 weeks; Dosing regimen of rifabutin: 150 mg every other day for 2 weeks; Study population (n): Healthy subjects (15); Effect on rifabutin: ↔ AUC compared to rifabutin 300 mg once a day alone ↓ C max by 15%; Effect on co-administered drug: ↑ AUC by 35% compared to historical control (fosamprenavir/ritonavir 700/100 mg twice a day), ↑ C max by 36%, ↑ C min by 36%; Recommendation: Reduce rifabutin dose by at least 75% (to a maximum 150 mg every other day or three times per week) when given with fosamprenavir/ritonavir combination.
Source: FDA drug label (Rifabutin), NDA050689 (Pfizer), as published by REMEDYREPACK INC., effective September 1, 2026 (SPL set 25a60937-cbbe-4a50-994f-2ce15203f589), 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
| Fosamprenavir | Rifabutin | |
|---|---|---|
| Labeled for | HIV | n/a |
| Boxed warning | No | No |
| Pharmacy cost (NADAC) | n/a | $8.14 per capsule 150 mg capsule |
| 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