What Is Prevymis? Uses, Dosage, and What You Need to Know in 2026

If your doctor has prescribed Prevymis after a stem cell or kidney transplant, you may have a lot of questions: What is this drug? Why do I need it? How do I take it? What will it cost? This guide answers all of those questions in plain language, so you know exactly what to expect.

What Is Prevymis?

Prevymis is the brand name for letermovir, an antiviral medication made by Merck. It was first approved by the U.S. Food and Drug Administration (FDA) on November 8, 2017. Prevymis belongs to a class of drugs called CMV DNA terminase complex inhibitors — a novel class of antiviral drugs with a mechanism of action completely different from older antivirals.

"CMV" stands for cytomegalovirus — a common herpesvirus that most people carry without symptoms. In healthy people, CMV stays dormant and harmless. But in patients whose immune systems have been suppressed after a transplant, CMV can reactivate and cause severe, potentially life-threatening illness.

What Is Prevymis Used For?

Prevymis is FDA-approved to prevent (not treat) CMV infection in two groups of transplant patients:

1. Allogeneic stem cell transplant (HSCT) recipients: Adults and children 6 months of age or older (at least 6 kg) who are CMV-seropositive (meaning their blood tests show they have been previously exposed to CMV, coded as R+).
2. High-risk kidney transplant recipients: Adults and children 12 years of age or older (at least 40 kg) where the donor had CMV but the recipient did not (D+/R-), a situation called "seronegative recipient of a seropositive donor" — the highest-risk scenario for CMV disease after kidney transplant.

CMV can cause serious problems in immunocompromised transplant patients, including pneumonia, hepatitis, retinitis (eye infection that can cause blindness), gastrointestinal disease, and a generalized CMV syndrome with fever, fatigue, and organ damage. Prevymis significantly reduces the risk of these complications.

What Forms Does Prevymis Come In?

Prevymis is available in multiple forms to suit different patients:

• 240 mg tablets — yellow oval tablets; used when co-administered with cyclosporine
• 480 mg tablets — pink oval tablets; standard dose for most patients not on cyclosporine
• 20 mg and 120 mg oral pellet packets — for children or patients who cannot swallow tablets; can be mixed with soft food or given via NG/G tube
• 240 mg and 480 mg IV injection vials — for inpatients who cannot take oral medication; infused over 1 hour; should be switched to oral form as soon as possible

How Is Prevymis Taken?

The standard dose for adults and older pediatric patients is 480 mg once daily. If you are also taking cyclosporine (a common transplant immunosuppressant), your dose is reduced to 240 mg once daily because cyclosporine increases letermovir blood levels.

• Tablets: Take once daily with or without food. Swallow whole — do not crush or chew.
• Oral pellets: Mix with soft food (like applesauce or pudding) or administer via NG tube or G tube. Do not crush the pellets.
• Duration: Up to 100 days post-HSCT (may extend to 200 days for high-risk patients); up to 200 days post-kidney transplant

Is Prevymis a Controlled Substance?

No. Prevymis is not a controlled substance. It does not appear on the DEA's schedules of controlled substances. Unlike many medications, there are no special restrictions on how it can be prescribed, dispensed, or refilled from a DEA scheduling standpoint. However, insurance prior authorization is required by most health plans before coverage is approved.

How Much Does Prevymis Cost?

Prevymis is an expensive specialty medication. The retail cash price is approximately $8,700–$9,053 per 30-day supply. With GoodRx or SingleCare coupons, the price drops to approximately $7,700. There is currently no FDA-approved generic.

Most commercially insured patients will pay much less — Merck's savings card allows eligible patients to pay as little as $15 per prescription. For uninsured patients, the Merck Access Program may cover the cost entirely based on income eligibility.

Where Can You Fill a Prevymis Prescription?

Prevymis is typically dispensed through specialty pharmacies, not standard retail locations. Your transplant center will usually direct you to a preferred pharmacy. If you need help finding a pharmacy that carries it, medfinder contacts pharmacies near you by phone and texts you which ones can fill your prescription.

Key Takeaways

• Prevymis (letermovir) is a first-in-class antiviral that prevents CMV infection in transplant patients
• It is taken once daily (480 mg standard dose; 240 mg with cyclosporine)
• Available as tablets, oral pellets, and IV injection
• Not a controlled substance; requires insurance prior authorization for most plans
• Significantly better bone marrow safety profile than valganciclovir

For a deeper look at how Prevymis works at the molecular level, see: How Does Prevymis Work? Mechanism of Action Explained.