What the FDA labels say about taking them together
Nafcillin and warfarin
Nafcillin's FDA label (Nafcillin) of December 6, 2024 names warfarin in its drug interactions section, and warfarin's label names nafcillin too. The nafcillin label: “Nafcillin in high dosage regimens, i.e., 2 grams every 4 hours, has been reported to decrease the effects of warfarin.”
Check it at the source: the nafcillin FDA label on DailyMed (effective March 9, 2026, ONESOURCE SPECIALTY PHARMA LIMITED); the warfarin FDA label on DailyMed (effective May 29, 2026, Amneal Pharmaceuticals LLC).
What does the nafcillin label say about warfarin?
Nafcillin label (Baxter Healthcare Corporation, December 6, 2024), drug interactionsNafcillin in high dosage regimens, i.e., 2 grams every 4 hours, has been reported to decrease the effects of warfarin.
Source: FDA drug label (Nafcillin, NDA050655), Baxter Healthcare Corporation, effective December 6, 2024 (SPL set cd2d18c5-95a2-4fb4-bd8b-b5d39e2da416), via openFDA
Source: FDA drug label (NAFCILLIN SODIUM), ONESOURCE SPECIALTY PHARMA LIMITED, effective March 9, 2026 (SPL set 4b3b8e52-df96-4886-e063-6294a90ac63f), via openFDA; the full label on DailyMed
What does the warfarin label say about nafcillin?
Warfarin label, drug interactions… nilotinib, oral contraceptives, posaconazole, ranitidine, ranolazine, ritonavir, saquinavir, telithromycin, tipranavir, voriconazole, zileuton armodafinil, amprenavir, aprepitant, bosentan, carbamazepine, efavirenz, etravirine, modafinil, nafcillin, phenytoin, pioglitazone, prednisone, rifampin, rufinamide
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
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
| Nafcillin | Warfarin | |
|---|---|---|
| Labeled for | n/a | Blood clots (DVT and PE), Atrial fibrillation |
| Boxed warning | No | Yes |
| Pharmacy cost (NADAC) | n/a | $0.093 per tablet 2 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