What the FDA labels say about taking them together
Warfarin and zafirlukast
Warfarin's FDA label of May 29, 2026 names zafirlukast in its drug interactions section, and zafirlukast's label names warfarin too. The zafirlukast label: “… doses of zafirlukast (160 mg/day) to steady-state with a single 25 mg dose of warfarin resulted in a significant increase in the mean AUC (+ 63%) and half-life (+36%) of S-warfarin.”
Check it at the source: the warfarin FDA label on DailyMed (effective May 29, 2026, Amneal Pharmaceuticals LLC); the zafirlukast FDA label on DailyMed (effective December 1, 2023, Aurobindo Pharma Limited).
What does the warfarin label say about zafirlukast?
Warfarin label, drug interactionsClosely monitor INR if a concomitant drug is a CYP2C9, 1A2, and/or 3A4 inhibitor or inducer. Examples of CYP450 Interactions with Warfarin Enzyme Inhibitors Inducers CYP2C9 amiodarone, capecitabine, cotrimoxazole, etravirine, fluconazole, fluvastatin, fluvoxamine, metronidazole, miconazole, oxandrolone, sulfinpyrazone, tigecycline, voriconazole, zafirlukast aprepitant, bosentan, carbamazepine, phenobarbital, rifampin CYP1A2 acyclovir, allopurinol, caffeine, cimetidine, ciprofloxacin, disulfiram, enoxacin, famotidine, fluvoxamine, methoxsalen, mexiletine, norfloxacin, oral contraceptives, phenylpropanolamine, propafenone, propranolol, terbinafine, thiabendazole, ticlopidine, verapamil …
Source: FDA drug label (Warfarin Sodium), Amneal Pharmaceuticals LLC, effective May 29, 2026 (SPL set 558b7a0d-5490-4c1b-802e-3ab3f1efe760), via openFDA; the full label on DailyMed
What does the zafirlukast label say about warfarin?
Zafirlukast label, drug interactionsDrug Interactions: In a drug interaction study in 16 healthy male volunteers, coadministration of multiple doses of zafirlukast (160 mg/day) to steady-state with a single 25 mg dose of warfarin resulted in a significant increase in the mean AUC (+ 63%) and half-life (+36%) of S-warfarin.
Zafirlukast label, warningsConcomitant Warfarin Administration: Coadministration of zafirlukast with warfarin results in a clinically significant increase in prothrombin time (PT).
Source: FDA drug label (Zafirlukast), Aurobindo Pharma Limited, effective December 1, 2023 (SPL set 8bdb47c5-9d19-4d59-94c8-62c117525e7f), 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
| Warfarin | Zafirlukast | |
|---|---|---|
| Labeled for | Blood clots (DVT and PE), Atrial fibrillation | Asthma |
| Boxed warning | Yes | No |
| Pharmacy cost (NADAC) | $0.093 per tablet 2 mg tablet | $0.623 per tablet 20 mg tablet |
| 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