Prevymis (Letermovir) — NZ Medication Guide | KiwiMeds
✅ Reviewed by Ramon Wong, BPharm, Registered Pharmacist (New Zealand) | May 2026 — This information is for educational purposes only and is not a substitute for personalised advice from your doctor or pharmacist. Always seek professional guidance before making changes to your medications.
What is Prevymis (letermovir)?
Prevymis (generic name: letermovir) is an antiviral medicine used to prevent cytomegalovirus (CMV) infection in people with severely weakened immune systems. CMV is a very common virus that stays dormant in the body for life but can cause serious — even life-threatening — illness in people whose immune systems are not working properly. Letermovir is taken as an oral tablet (and is also available as an IV formulation for use in hospitals).
What is it used for? (NZ context)
In New Zealand, letermovir (Prevymis) is funded by Pharmac from 1 May 2026 for:
- Adults who have had an allogeneic haematopoietic stem cell transplant (allo-HSCT) — also called a bone marrow transplant — to prevent CMV infection during the high-risk period after transplant
- A small number of other people with severe immunosuppression who cannot use other funded antiviral medicines
How does it work?
Letermovir belongs to a new class of antivirals called CMV terminase inhibitors. During CMV replication, the virus uses an enzyme called terminase to cut and package its DNA into new viral particles. Letermovir blocks this terminase enzyme, preventing the virus from assembling new copies of itself. This stops CMV from replicating and spreading through the body. Importantly, letermovir works through a completely different mechanism to older antiviral medicines like ganciclovir or valganciclovir, making it a valuable option for patients who have experienced toxicity or resistance to those medicines.
How to take it
Letermovir (Prevymis) is taken as a tablet once daily.
- Take with or without food
- Swallow whole — do not crush or chew
- Take at approximately the same time each day
- Treatment is usually started shortly after the stem cell transplant and continued for up to 100 days post-transplant (or longer in some cases, as directed by your specialist)
If you miss a dose: take it as soon as you remember that same day. If you remember the next day, skip the missed dose and continue your regular schedule. Never double up.
Common side effects
Letermovir is generally well tolerated. Common side effects include:
- Nausea
- Vomiting
- Diarrhoea
- Abdominal (tummy) pain
- Fatigue (tiredness)
- Headache
- Oedema (swelling, often in the legs)
Serious side effects to watch for
Letermovir is considered safer than older CMV antivirals (ganciclovir/valganciclovir) as it does not suppress bone marrow. However, contact your transplant team if you experience:
- Signs of CMV infection despite treatment — fever, fatigue, shortness of breath, diarrhoea, visual changes — as a small number of people may not respond or may develop resistance
- Severe nausea, vomiting, or inability to take oral medicines — your team may need to switch to IV letermovir
- Rapid heart rate or palpitations — letermovir can affect the heart rhythm in some patients, particularly those also on cyclosporine
- Any signs of organ transplant rejection — though not directly caused by letermovir, reporting all symptoms is important in the post-transplant period
Important drug interactions
Letermovir has several important drug interactions, many relevant to post-transplant patients:
Cyclosporine (calcineurin inhibitor): When taken with cyclosporine, letermovir blood levels are significantly increased (2-fold) and the letermovir dose is reduced to 240 mg/day (from 480 mg/day). Your transplant team will manage this. Cyclosporine levels may also be affected.
Other important interactions include:
- Tacrolimus — letermovir may increase tacrolimus levels; close monitoring required
- Sirolimus — similar monitoring needed
- Statins (cholesterol-lowering medicines) — levels may increase; dose adjustment may be needed
- Pimozide, ergotamine — avoid
- Rifampicin — reduces letermovir levels
Things to avoid while taking it
- Missing doses — consistent daily dosing is critical to prevent CMV reactivation
- Live vaccines — not appropriate in the post-transplant immunosuppressed period
- Starting new medicines without checking — many post-transplant medicines interact with letermovir; always check with your transplant pharmacist
NZ-specific information
Brand name in NZ: Prevymis
Funded: Yes — from 1 May 2026 for post-allo-HSCT CMV prevention and selected severely immunosuppressed patients
Available as: Oral tablets (240 mg, 480 mg); IV formulation also available for hospital use
Special Authority: Required — managed by your transplant centre
Prescription type: Hospital specialist
Previously, letermovir was not funded in NZ and patients either received older antivirals with more side effects (ganciclovir/valganciclovir, which suppress bone marrow) or had to pay privately. This funding decision is significant for the approximately 90 New Zealanders who undergo allo-HSCT each year.
Frequently asked questions
Why do stem cell transplant patients need antiviral medicines?
After an allo-HSCT, your immune system is severely weakened. CMV — a virus that lives dormant in most adults — can reactivate and cause serious illness. Letermovir prevents this from happening during the high-risk period when your immune system is rebuilding.
Will letermovir cure a CMV infection?
No — letermovir is used for prevention, not treatment. If CMV infection is confirmed (by blood test), a different antiviral treatment (ganciclovir, valganciclovir, or foscarnet) is usually required.
How long will I need letermovir?
Usually for the first 100 days after transplant, which is the highest-risk period. Some patients may receive it for longer — your transplant team will decide.
Is letermovir safe for the kidneys?
Unlike some older CMV antivirals, letermovir does not appear to cause significant kidney toxicity. Your team will still monitor kidney function as part of routine post-transplant care.
Related medications
- Valganciclovir — older CMV antiviral (treatment if prevention fails)
- Ganciclovir — IV CMV treatment used in hospital