What the FDA labels say about taking them together
Letermovir and sirolimus
Letermovir's FDA label of January 14, 2026 names sirolimus in its drug interactions section, and sirolimus's label names letermovir too. The letermovir label: “When PREVYMIS is co-administered with sirolimus, frequently monitor sirolimus whole blood concentrations during treatment and after discontinuation of PREVYMIS and adjust the dose of sirolimus accordingly. …”
Check it at the source: the letermovir FDA label on DailyMed (effective January 14, 2026, Merck Sharp & Dohme LLC); the sirolimus FDA label on DailyMed (effective January 28, 2026, Glenmark Pharmaceuticals Inc., USA).
What does the letermovir label say about sirolimus?
Letermovir label, drug interactionsConcomitant Drug Class and/or Clearance Pathway/Drug Name: sirolimus; Effect on Concentration ↓ =decrease, ↑ =increase: ↑ sirolimus; Clinical Comments: When PREVYMIS is co-administered with sirolimus, frequently monitor sirolimus whole blood concentrations during treatment and after discontinuation of PREVYMIS and adjust the dose of sirolimus accordingly. When PREVYMIS is co-administered with cyclosporine and sirolimus, refer to the sirolimus prescribing information for specific sirolimus dosing recommendations.
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 sirolimus label say about letermovir?
Sirolimus label, drug interactionsDrugs that could increase sirolimus blood concentrations: Bromocriptine, cimetidine, cisapride, clotrimazole, danazol, diltiazem, fluconazole, letermovir, protease inhibitors (e.g., HIV and hepatitis C that include drugs such as ritonavir, indinavir, boceprevir, and telaprevir), metoclopramide, nicardipine, troleandomycin, verapamil
Source: FDA drug label (sirolimus), Glenmark Pharmaceuticals Inc., USA, effective January 28, 2026 (SPL set 57fb4d90-3ccb-4a69-af1e-53be83f7a504), 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 | Sirolimus | |
|---|---|---|
| Labeled for | n/a | Organ transplant rejection |
| Boxed warning | No | Yes |
| Pharmacy cost (NADAC) | n/a | $0.723 per tablet 1 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