What the FDA labels say about taking them together
Nelfinavir and rifabutin
Nelfinavir's FDA label of December 11, 2025 names rifabutin in its drug interactions section, and rifabutin's label names nelfinavir too. The rifabutin label: “Reduce rifabutin dose by 50% (to 150 mg once a day) and increase the nelfinavir dose to 1250 mg twice a day.”
Check it at the source: the nelfinavir FDA label on DailyMed (effective December 11, 2025, AGOURON); the rifabutin FDA label on DailyMed (effective September 1, 2026, REMEDYREPACK INC.).
What does the nelfinavir label say about rifabutin?
Nelfinavir label, drug interactionsConcomitant Drug Class/Drug Name: Rifabutin; Effect on Concentration: ↑ rifabutin ↓ nelfinavir (750 mg TID) ↔ nelfinavir (1250 mg BID); Clinical Comment: It is recommended that the dose of rifabutin be reduced to one-half the usual dose when administered with VIRACEPT; 1250 mg BID is the preferred dose of VIRACEPT when coadministered with rifabutin.
Source: FDA drug label (VIRACEPT), AGOURON, effective December 11, 2025 (SPL set e72c2bc6-9462-4a2e-8e1d-b97592376cbd), via openFDA; the full label on DailyMed
What does the rifabutin label say about nelfinavir?
Rifabutin label, drug interactionsCo-administered drug: Nelfinavir; Dosing regimen of co-administered drug: 1250 mg twice a day for 7–8 days; Dosing regimen of rifabutin: 150 mg once a day for 8 days; Study population (n): HIV-infected patients (11); Effect on rifabutin: ↑ AUC by 83%, compared to rifabutin 300 mg once a day alone ↑ C max by 19%; Effect on co-administered drug: ↔; Recommendation: Reduce rifabutin dose by 50% (to 150 mg once a day) and increase the nelfinavir dose to 1250 mg twice a day.
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
| Nelfinavir | 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