What the FDA labels say about taking them together
Isoniazid and rifampin
Isoniazid's FDA label of July 8, 2025 names rifampin in its drug interactions section; the rifampin label PlainMeds reads does not name isoniazid. The isoniazid label: “When ketoconazole is given in combination with isoniazid and rifampin the AUC of ketoconazole is decreased by as much as 88% after 5 months of concurrent isoniazid and rifampin therapy 4.”
Check it at the source: the isoniazid FDA label on DailyMed (effective July 8, 2025, OMNIVIUM PHARMACEUTICALS LLC.); the rifampin FDA label on DailyMed (effective February 11, 2026, Lupin Pharmaceuticals, Inc.).
What does the isoniazid label say about rifampin?
Isoniazid label, drug interactionsWhen ketoconazole is given in combination with isoniazid and rifampin the AUC of ketoconazole is decreased by as much as 88% after 5 months of concurrent isoniazid and rifampin therapy 4 .
Source: FDA drug label (isoniazid), OMNIVIUM PHARMACEUTICALS LLC., effective July 8, 2025 (SPL set 35400f1d-fd25-4bfa-a382-ac390e21bf2e), via openFDA; the full label on DailyMed
What does the rifampin label say about isoniazid?
Rifampin's label (effective February 11, 2026) does not name isoniazid in these sections. A label lists what its studies and reports found; it is not a complete list.
Source: FDA drug label (rifampin), Lupin Pharmaceuticals, Inc., effective February 11, 2026 (SPL set b56004f0-f23d-47f6-80c7-39884fccbccc), 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
| Isoniazid | Rifampin | |
|---|---|---|
| Labeled for | n/a | n/a |
| Boxed warning | Yes | No |
| Pharmacy cost (NADAC) | $3.40 per tablet 300 mg tablet | $0.679 per capsule 300 mg capsule |
| Shortage now | No current entry | In shortage |
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