Prevymis (Letermovir) Complete Guide

Prevymis (letermovir) is an antiviral medicine used to prevent cytomegalovirus (CMV) infection after a stem cell transplant or a high-risk kidney transplant. This guide covers how Prevymis works, its side effects, how it is taken, drug interactions and what it costs. If you need help paying for it, see our Prevymis (letermovir) copay assistance page.

What Is Prevymis (Letermovir)?

Prevymis (letermovir) is an antiviral first approved by the FDA on November 8, 2017, to prevent CMV in certain transplant patients. It is approved for:

• Stem cell (allogeneic hematopoietic cell) transplant: adults and children 6 months and older weighing at least 6 kg who are CMV-seropositive recipients.
• High-risk kidney transplant: adults and children 12 years and older weighing at least 40 kg, when the donor is CMV-positive and the recipient is CMV-negative (D+/R-).

Prevymis comes as tablets (240 mg and 480 mg), oral pellet packets (20 mg and 120 mg) and an IV solution. MedlinePlus has a plain-language overview.

Source: Lexidrug, letermovir monograph (accessed 9/30/2026); Prevymis prescribing information, Merck Sharp & Dohme LLC, January 2026. Not a complete list. Follow your transplant team’s instructions.

How Does Prevymis Work?

Prevymis stops CMV from copying itself by blocking the virus’s DNA terminase complex, a part CMV needs to package its DNA. It works only against CMV. It does not protect against herpes simplex virus, so your transplant team may add another antiviral, such as acyclovir.

Source: Lexidrug, letermovir monograph (accessed 9/30/2026); Prevymis prescribing information, Merck Sharp & Dohme LLC, January 2026. Not a complete list. Follow your transplant team’s instructions.

Prevymis Side Effects

The most common Prevymis side effects are nausea, diarrhea, vomiting, swelling in the arms or legs, cough, headache and tiredness. In adults, Lexidrug lists these as reported in more than 10% of patients:

• Nausea (27%), diarrhea (26%) and vomiting (19%)
• Swelling in the arms or legs (14%)
• Cough (14%) and headache (14%)
• Tiredness (13%)
• Heart rhythm changes (13%, including atrial fibrillation 3% and fast heartbeat 4%)
• Stomach pain (12%)
• Low platelet counts

Call your doctor right away for a fast or abnormal heartbeat, swelling, a change in how much you urinate, signs of infection, unexplained bruising or bleeding, or signs of an allergic reaction. With the IV form, also report ringing in the ears or hearing changes.

“Nausea and diarrhea are among the side effects reported most often with Prevymis, and heart rhythm changes and swelling are also on the list.* If you notice any of these, call your transplant team or our pharmacists before you skip a dose, because Prevymis is part of a prevention plan that is timed around your transplant.”

Julia Kravtsova, PharmD, Head Patient Navigator, QuickRx Specialty Pharmacy

*Source: Lexidrug, letermovir monograph (Adverse Reactions, Dosing), accessed 9/30/2026. This quote is general information, not medical advice for your own treatment. Do not start, stop, skip or change how you take this medicine without talking to your prescriber, and always follow your prescriber’s instructions and the FDA-approved labeling.

Source: Lexidrug, letermovir monograph (accessed 9/30/2026); Prevymis prescribing information, Merck Sharp & Dohme LLC, January 2026. Not a complete list. Follow your transplant team’s instructions.

Prevymis Warnings and Precautions

The main precautions with Prevymis involve other viruses, resistance, the IV form, and kidney and liver function.

• Other viruses: Prevymis is not active against herpes viruses other than CMV.
• Resistance: CMV can become resistant to letermovir through changes in a viral gene called UL56.
• IV form: contains hydroxypropyl betadex; it is meant for patients who cannot take it by mouth, should be switched to oral as soon as possible and, if possible, not used for more than 4 weeks.
• Kidney: with the IV form, kidney function is watched closely when CrCl is below 50 mL/minute.
• Liver: use is not recommended with severe liver problems (Child-Pugh C).

Source: Lexidrug, letermovir monograph (accessed 9/30/2026); Prevymis prescribing information, Merck Sharp & Dohme LLC, January 2026. Not a complete list. Follow your transplant team’s instructions.

How Is Prevymis Taken?

The usual adult dose of Prevymis is 480 mg once a day, by mouth or by IV.

• After a stem cell transplant: usually started between day 0 and day 28 and continued through day 100; some patients at risk for late CMV continue through day 200.
• After a high-risk kidney transplant: usually started between day 0 and day 7 and continued through day 200.
• With cyclosporine: the Prevymis dose is lowered; your transplant team sets the exact dose.
• Tablets: take with or without food; swallow whole.
• Oral pellets: do not crush or chew; mix with 1 to 3 teaspoons of soft food at or below room temperature (such as applesauce, yogurt or pudding) and take within 10 minutes.

Kidney and Liver Dosing

No dose change is needed when CrCl is above 10 mL/minute. The labeling gives no dose advice for CrCl of 10 or less or for dialysis, though Lexidrug notes a change is unlikely because very little leaves the body in urine. No change is needed for mild or moderate liver problems.

Always follow the exact dose and schedule your transplant team gives you. Source: Lexidrug, letermovir monograph (accessed 9/30/2026).

Does Prevymis Interact With Other Drugs?

Yes, Prevymis has many important drug interactions, including with common transplant medicines.

• Do not combine: pimozide or ergot medicines; pitavastatin or simvastatin when you also take cyclosporine.
• Transplant medicines: Prevymis and cyclosporine raise each other’s levels; sirolimus doses will likely need lowering; tacrolimus levels are monitored.
• Other medicines: Prevymis may lower voriconazole levels and may affect warfarin. Atorvastatin is limited to 20 mg a day with Prevymis and is not recommended when cyclosporine is also used. Carbamazepine should be avoided.

Tell every doctor and pharmacist about every medicine and supplement you take. QuickRx pharmacists can review your list; call (917) 830-2525.

Source: Lexidrug, letermovir monograph (accessed 9/30/2026); Prevymis prescribing information, Merck Sharp & Dohme LLC, January 2026. Not a complete list. Follow your transplant team’s instructions.

What Monitoring Is Needed on Prevymis?

Your transplant team will watch for CMV coming back and will check your kidney function. Kidney checks (serum creatinine) matter most if you receive the IV form and your CrCl is below 50 mL/minute.

Source: Lexidrug, letermovir monograph (accessed 9/30/2026); Prevymis prescribing information, Merck Sharp & Dohme LLC, January 2026. Not a complete list. Follow your transplant team’s instructions.

Can You Take Prevymis During Pregnancy or Breastfeeding?

Some animal studies showed harmful effects, and it is not known whether letermovir passes into breast milk. Talk with your transplant team about the risks and benefits if you are pregnant, planning a pregnancy or breastfeeding.

Source: Lexidrug, letermovir monograph (accessed 9/30/2026); Prevymis prescribing information, Merck Sharp & Dohme LLC, January 2026. Not a complete list. Follow your transplant team’s instructions.

Is There a Generic, and How Much Does Prevymis Cost?

No, there is no generic letermovir in the United States, and at Average Wholesale Price a 30-day supply of tablets is about $10,125.

Copay cards, patient assistance programs and foundation grants may lower what you pay. QuickRx applies on your behalf. Learn more on our Prevymis (letermovir) copay assistance page or call (917) 830-2525.

Eligibility and availability are set by each manufacturer or foundation, not by QuickRx. Not all patients qualify. Manufacturer copay coupons generally cannot be used by patients whose prescriptions are paid for by Medicare, Medicaid or other federal health care programs (HHS OIG, 2014).

Is Prevymis Used After Other Organ Transplants?

Yes, as an off-label use, Prevymis is used to prevent CMV after some liver, lung, heart and kidney transplants. Lexidrug cites the Fourth International Consensus Guidelines on CMV in Solid Organ Transplantation (2025), which list letermovir as an alternative for at-risk patients who cannot tolerate other antivirals such as valganciclovir.

Off-label means the use is not approved by the FDA for that condition. Insurance coverage and assistance eligibility for off-label use may differ.

How Should Prevymis Be Stored?

Store Prevymis tablets and oral pellets at room temperature, 20°C to 25°C (68°F to 77°F). Keep tablets in the original container to protect them from moisture, and keep pellets in the original packet. Brief exposure to 15°C to 30°C (59°F to 86°F) is allowed.

Source: Lexidrug, letermovir monograph (accessed 9/30/2026); Prevymis prescribing information, Merck Sharp & Dohme LLC, January 2026. Not a complete list. Follow your transplant team’s instructions.

Prevymis FAQs

References

1. Letermovir. Lexidrug via UpToDate (Wolters Kluwer Health). Accessed September 30, 2026. (Subscription required.)
2. Letermovir. MedlinePlus, US National Library of Medicine.
3. Marty FM, Ljungman P, Chemaly RF, et al. Letermovir prophylaxis for cytomegalovirus in hematopoietic-cell transplantation. N Engl J Med. 2017;377(25):2433-2444. PubMed 29211658
4. Limaye AP, Budde K, Humar A, et al. Letermovir vs valganciclovir for prophylaxis of cytomegalovirus in high-risk kidney transplant recipients: a randomized clinical trial. JAMA. 2023. PubMed 37279999
5. Kotton CN, Kumar D, Manuel O, et al. The Fourth International Consensus Guidelines on the Management of Cytomegalovirus in Solid Organ Transplantation. Transplantation. 2025;109(7):1066-1110. PubMed 40200403
6. HHS Office of Inspector General. Special Advisory Bulletin: Pharmaceutical Manufacturer Copayment Coupons. September 2014.

Prescribing information: Prevymis (letermovir) tablets, pellets, and injection. Rahway, NJ: Merck Sharp & Dohme LLC; January 2026.

Need help paying for Prevymis? Call QuickRx at (917) 830-2525 or visit our Prevymis (letermovir) copay assistance page.