Letermovir
Pronunciation: pronunciation varies by local usage.
- Generic name
- letermovir
- Brand names
- PREVYMIS
- Drug class
- Cytomegalovirus (CMV) DNA terminase complex inhibitor
- Form
- Tablets 240 mg or 480 mg; oral pellets 20 mg or 120 mg packets; concentrate for intravenous infusion
- Route
- Oral (tablet or pellets) or intravenous infusion
- Legal status
- Prescription-only medicine
Availability and supply rules vary by country
Trade names by country: United States
Australia: · Full directory
What letermovir is and how it works
Letermovir is an antiviral medicine that inhibits the CMV DNA terminase complex. It is used to prevent cytomegalovirus (CMV) infection or disease in certain transplant recipients. (1)
The approved uses, minimum age, and weight criteria depend on the type of transplant. Letermovir is a preventive (prophylactic) treatment, not a treatment for established CMV disease. A specialist transplant team must confirm eligibility, dosing, and the monitoring plan.
Mechanism of action: how letermovir works
Letermovir inhibits the CMV DNA terminase complex, an enzyme specific to CMV and required for viral DNA processing and packaging into capsids. (1)
What letermovir is used for
CMV prophylaxis in allogeneic haematopoietic stem cell transplant (HSCT)
For the prevention of CMV infection and disease in CMV-seropositive recipients (R+) of an allogeneic HSCT, in adults and paediatric patients 6 months of age and older and weighing at least 6 kg. (1)
CMV prophylaxis in kidney transplant
For the prevention of CMV disease in adults and paediatric patients 12 years of age and older and weighing at least 40 kg, who are kidney transplant recipients at high risk (donor CMV-seropositive, recipient CMV-seronegative — D+/R-). (1)
Before taking letermovir
Do not take / not appropriate for
- Tell the transplant team or prescriber if you take pimozide, ergot alkaloids, or (if you also take cyclosporine) pitavastatin or simvastatin. These combinations are contraindicated with letermovir (risk of QT prolongation with pimozide, ergotism with ergot alkaloids); the transplant team manages this. (all products) (1)
Tell your clinician about
- All prescription and non-prescription medicines, vitamins, and herbal supplements you are taking, especially cyclosporine, tacrolimus, sirolimus, statins, warfarin, antiarrhythmics, or any medicine listed as not recommended with letermovir.
- If you have, or have ever had, kidney or liver problems.
- If you are pregnant, planning to become pregnant, or are breastfeeding.
- Any side effects or new symptoms that develop during treatment.
How to take letermovir
- Take letermovir exactly as prescribed by the transplant specialist. The dose and duration depend on the type of transplant, age, weight, and whether you are also taking cyclosporine.
- Oral tablets should be swallowed whole with or without food. Do not crush or chew the tablets.
- Oral pellets must be mixed with soft food or given through a nasogastric or gastric tube, following the exact instructions provided.
- The intravenous (IV) form is given by infusion over 1 hour in a healthcare setting, typically when you cannot take the medicine by mouth.
- Any change to the dose, continuation, or oral/IV formulation is decided by the transplant team.
Procedures and treatment changes
Tell the treating team before surgery, procedures, or any medicine change. Do not alter treatment without the responsible clinician. (1)
Missed dose
Contact the transplant team for advice.
Overdose
There is no specific antidote for letermovir overdose; management involves monitoring for adverse reactions and symptomatic treatment. Contact the transplant team promptly if you think you may have received too much letermovir. (1)
Side effects
Side effects can vary with the type of transplant and the patient's age. The most common effects in clinical trials are listed below. Letermovir can also have serious drug interactions.
Gastrointestinal effects and general symptoms
What to notice: For adult HSCT recipients, nausea (27%), diarrhoea (26%), vomiting (19%), fatigue (13%), and abdominal pain (12%) were reported. For adult kidney transplant recipients, diarrhoea was the most common (32%).
What to do: Tell the transplant team if these effects are severe, persistent, or worsen. (1)
Other common effects in HSCT
What to notice: Peripheral edema (14%), cough (14%), and headache (14%).
What to do: Report any persistent or troublesome symptoms to the transplant team. (1)
Cardiac events
What to notice: Not established from the sources reviewed: a specific patient-facing symptom checklist was not established in the sources reviewed for this page beyond the named risks. In studies, cardiac events including tachycardia and atrial fibrillation were more frequent with letermovir than with placebo (13% vs 6%).
What to do: Contact the transplant team if you experience any symptom you believe may be cardiac-related, such as tachycardia or an irregular heartbeat. (1)
Kidney function changes with IV formulation
What to do: Attend all scheduled blood tests as directed by the transplant team. (1)
Serious warnings
Severe drug interactions — significant
Symptoms: Letermovir can cause significant changes in the blood levels of many other medicines, including immunosuppressants (tacrolimus, sirolimus, cyclosporine), antiarrhythmics, statins, anticoagulants, and others. This can increase the risk of serious side effects or reduce the effectiveness of treatment.
Action: The transplant team decides on starting, continuing, changing, or discontinuing any co-administered medicine, supplement, or herbal product; tell them about all products you take. Seek urgent medical advice if you develop any symptom that concerns you. (1)
Interactions
| Medicine or test | Effect | Action |
|---|---|---|
| Immunosuppressants (cyclosporine, tacrolimus, sirolimus) | Letermovir can increase tacrolimus and sirolimus blood levels substantially. Co-administration with cyclosporine can increase letermovir levels and requires a halving of the letermovir dose. | Blood levels of cyclosporine, tacrolimus, and sirolimus must be monitored closely and doses adjusted by the transplant team. (1) |
| Warfarin | The label recommends frequent INR monitoring during concurrent use. | The prescriber monitors INR frequently and adjusts the warfarin dose accordingly. (1) |
| Statins (e.g., atorvastatin, pravastatin) | Letermovir can increase statin levels, raising the risk of muscle injury (myopathy). | The label supports a 20 mg/day atorvastatin maximum with monitoring for myopathy; the prescriber or transplant team manages any statin-dose limit or change. (1) |
| Medicines not recommended for co-administration | Co-administration with nafcillin, carbamazepine, phenobarbital, phenytoin, rifabutin, rifampin, efavirenz, etravirine, nevirapine, bosentan, modafinil, St. John's wort, thioridazine, pimozide, or ergot alkaloids can lead to reduced letermovir efficacy or serious adverse effects. | Give the specialist a complete list of all medicines and supplements; the specialist decides whether these combinations are appropriate. (1) |
Pregnancy, breastfeeding, kidney/liver function, age
Children and adolescents
Use in HSCT is established for patients 6 months of age and older weighing at least 6 kg. Use in kidney transplant is established for patients 12 years and older weighing at least 40 kg. Safety and efficacy have not been established for younger or lower-weight patients in each respective transplant type. A paediatric weight-based dosing table is used. (1)
Pregnancy and breastfeeding
There are no adequate human data to establish safety in pregnancy. Animal studies showed embryo-fetal toxicity at high exposures. It is unknown whether letermovir passes into human breast milk; it has been detected in rat milk. Discuss the risks and benefits with the transplant specialist. (1)
Older adults
No age-based dosage adjustment is required. Safety and efficacy have been shown to be similar in people 65 years of age and older. (1)
People with kidney impairment
No dose adjustment is required for creatinine clearance (CLcr) above 10 mL/min. If you are receiving the IV formulation and your CLcr is below 50 mL/min, your kidney function will be monitored closely due to an ingredient in the IV formulation. Safety in people with CLcr below 10 mL/min or on dialysis is unknown. (1)
People with liver impairment
No dose adjustment is needed for mild (Child-Pugh A) or moderate (Child-Pugh B) liver impairment. Use is not recommended in severe (Child-Pugh C) liver impairment. (1)
Monitoring
Before starting
- Confirm the exact transplant type, CMV serostatus, and that the patient meets the indication's age and weight criteria.
- Review the complete list of current medications for potentially serious drug-drug interactions.
During treatment
- Monitor CMV DNA levels weekly until Week 14 post-transplant, then every two weeks until Week 24 for HSCT recipients. Monitor for late CMV reactivation after stopping prophylaxis.
- Closely monitor and adjust blood levels of cyclosporine, tacrolimus, and sirolimus when co-administered.
- Monitor serum creatinine closely in patients with CLcr below 50 mL/min receiving the IV formulation.
- Monitor glucose if co-administered with glyburide, repaglinide, or rosiglitazone.
- Monitor INR frequently if co-administered with warfarin.
- Review concomitant medications regularly for newly started drugs that may interact.
Storage
Follow the storage instructions on the product packaging.
Professional information
Clinician-facing context only. This summary is based on the US prescribing information and may not reflect all regional labels. Always use the current local product information.
United States
Indication: HSCT CMV prophylaxis without cyclosporine
Dose summary: Adults and paediatric patients ≥12 years and ≥30 kg: 480 mg once daily. Paediatric patients <12 years: weight-based dosing (6 to <7.5 kg: 80 mg/day; 7.5 to <15 kg: 120 mg/day; 15 to <30 kg: 240 mg/day). Start Day 0 up to Day 100 post-transplant; may extend to Day 200 if at continued risk.
Renal context: No dose adjustment for CLcr >10 mL/min. For IV formulation in patients with CLcr <50 mL/min, monitor serum creatinine due to hydroxypropyl betadex accumulation. Safety unknown for CLcr <10 mL/min or on dialysis. (1)
United States
Indication: Kidney transplant CMV prophylaxis without cyclosporine
Dose summary: Adults and paediatric patients ≥12 years and ≥40 kg: 480 mg once daily. Initiate as early as Day 0 and up to Day 7, continue through Day 200 post-transplant.
Renal context: No dose adjustment for CLcr >10 mL/min. For IV formulation in patients with CLcr <50 mL/min, monitor serum creatinine due to hydroxypropyl betadex accumulation. Safety unknown for CLcr <10 mL/min or on dialysis. (1)
United States
Indication: All indications with cyclosporine co-administration
Dose summary: Adults and paediatric patients ≥12 years: reduce letermovir dose to 240 mg once daily. Paediatric patients <12 years: dose adjustment may be required per the complete weight-based dosing table.
Renal context: As above. The drug interaction with cyclosporine also increases letermovir exposure, necessitating the dose reduction. (1)
Hepatic guidance
No dose adjustment is needed for mild-to-moderate (Child-Pugh A or B) impairment. Use is not recommended in severe (Child-Pugh C) impairment.
Overdose note
No specific antidote exists. Management is monitoring for adverse reactions and symptomatic treatment. It is unclear whether haemodialysis significantly removes letermovir. (1)
Frequently asked questions
Can letermovir treat an active CMV infection?
No. Letermovir is used for the prevention of CMV infection and disease, not for its treatment. Your transplant team will monitor you for CMV during and after prophylaxis. (1)
Do I still need CMV monitoring while taking letermovir?
Yes. Regular CMV DNA blood tests are essential during and after letermovir prophylaxis to detect any reactivation of the virus. (1)
What should I do if I am taking cyclosporine?
Your letermovir dose will be adjusted by the transplant team, as cyclosporine can increase letermovir levels. Never change the dose yourself. (1)
What is the mechanism of action of letermovir?
Letermovir inhibits the CMV DNA terminase complex, an enzyme specific to CMV and required for viral DNA processing and packaging into capsids. (1)
What is the generic name of Letermovir?
The generic name is letermovir. It is sold under brand names including PREVYMIS. (1)
What class of drug is letermovir?
Letermovir is classed as: Cytomegalovirus (CMV) DNA terminase complex inhibitor. (1)
References
- PREVYMIS (letermovir) tablets, oral pellets, injection — prescribing informationU.S. Food and Drug Administration (DailyMed) · United States · accessed 2026-08-05 · source 1
- PREVYMIS (LETERMOVIR) TABLET, FILM COATED PREVYMIS (LETERMOVIR) INJECTION, SOLUTION PREVYMIS (LETERMOVIR) PELLET [MERCK SHARP & DOHME LLC] — US prescribing information (DailyMed SPL)U.S. National Library of Medicine (DailyMed) · US · accessed 2026-08-14 · source 2
- Letermovir — patient drug information (MedlinePlus)U.S. National Library of Medicine (MedlinePlus) · US · accessed 2026-08-14 · source 3
- PREVYMIS — FDA approval record (Drugs@FDA NDA209939)U.S. Food and Drug Administration · US · accessed 2026-08-14 · source 4
- letermovir — RxNorm normalized drug concept (RXCUI 1988648)U.S. National Library of Medicine (RxNorm) · US · accessed 2026-08-14 · source 5
Brand names by country
Single-ingredient letermovir names are shown separately by country. Product availability, strengths, and supply rules can change; combination products are not included here.
Priority countries
United States
- PREVYMIS20 mg, 240 mg, 120 mg, 480 mg, 20 mg/mL · merck sharp & dohme llc