What the FDA labels say about taking them together
Acyclovir and warfarin
Warfarin's FDA label of May 29, 2026 names acyclovir in its drug interactions section; the acyclovir labels PlainMeds reads (4) do not name warfarin. The warfarin label: “… zafirlukast aprepitant, bosentan, carbamazepine, phenobarbital, rifampin CYP1A2 acyclovir, allopurinol, caffeine, cimetidine, ciprofloxacin, disulfiram, enoxacin, famotidine, fluvoxamine, methoxsalen, mexiletine …”
Check it at the source: the acyclovir FDA label on DailyMed (effective July 24, 2026, Heritage Pharmaceuticals Inc. d/b/a Avet Pharmaceuticals Inc.); the warfarin FDA label on DailyMed (effective May 29, 2026, Amneal Pharmaceuticals LLC).
What does the acyclovir label say about warfarin?
Acyclovir's label (effective July 24, 2026) and its 3 other brand-application labels do not name warfarin in these sections. A label lists what its studies and reports found; it is not a complete list.
Source: FDA drug label (ACYCLOVIR), Heritage Pharmaceuticals Inc. d/b/a Avet Pharmaceuticals Inc., effective July 24, 2026 (SPL set 0de2f5c7-9e75-4bdf-9c28-e026cc6694b4), via openFDA; the full label on DailyMed
What does the warfarin label say about acyclovir?
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
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
| Acyclovir | Warfarin | |
|---|---|---|
| Labeled for | Herpes and shingles | Blood clots (DVT and PE), Atrial fibrillation |
| Boxed warning | No | Yes |
| Pharmacy cost (NADAC) | $0.0962 per tablet 400 mg tablet | $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