What the FDA labels say about taking them together
Letermovir and warfarin
Letermovir's FDA label of January 14, 2026 names warfarin in its drug interactions section; the warfarin label PlainMeds reads does not name letermovir. The letermovir label: “When PREVYMIS is co-administered with warfarin, frequently monitor International Normalized Ratio (INR) Refer to the respective prescribing information..”
Check it at the source: the letermovir FDA label on DailyMed (effective January 14, 2026, Merck Sharp & Dohme LLC); the warfarin FDA label on DailyMed (effective May 29, 2026, Amneal Pharmaceuticals LLC).
What does the letermovir label say about warfarin?
Letermovir label, drug interactionsConcomitant Drug Class and/or Clearance Pathway/Drug Name: warfarin; Effect on Concentration ↓ =decrease, ↑ =increase: ↓ warfarin; Clinical Comments: When PREVYMIS is co-administered with warfarin, frequently monitor International Normalized Ratio (INR) Refer to the respective prescribing information..
Source: FDA drug label (PREVYMIS), Merck Sharp & Dohme LLC, effective January 14, 2026 (SPL set 1b49df80-be4f-47e0-a0b7-123f3e69395b), via openFDA; the full label on DailyMed
What does the warfarin label say about letermovir?
Warfarin's label (effective May 29, 2026) does not name letermovir in these sections. A label lists what its studies and reports found; it is not a complete list.
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
| Letermovir | 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