Letermovir is used to help prevent cytomegalovirus (CMV) infection and disease in certain people who have received a hematopoietic stem-cell transplant (HSCT; a procedure that replaces diseased bone marrow with healthy bone marrow) and are at increased risk of developing a CMV infection. Letermovir is in a class of medications called antivirals. It works by slowing the growth of CMV.

Side Effects Of Letermovir

Letermovir may cause side effects. Tell your doctor if any of these symptoms are severe or do not go away:

  • nausea
  • vomiting
  • diarrhea
  • abdominal pain
  • swelling of your arms or legs
  • headache
  • extreme tiredness

Some side effects can be serious. If you experience any of these symptoms call your doctor immediately:

  • fast or irregular heartbeat; feeling weak or dizzy, shortness of breath, chest pain
  • Letermovir may cause other side effects. Call your doctor if you have any unusual problems while taking this medication.

Warnings & Precautions

Before taking letermovir:

  • tell your doctor and pharmacist if you are allergic to letermovir, any other medications, or any of the ingredients in letermovir tablets. Ask your pharmacist for a list of the ingredients.
  • tell your doctor if you are taking ergot alkaloids such as ergotamine (Ergomar, in Cafergot, Migergot), and dihydroergotamine (D.H.E. 45, Migranal), and pimozide (Orap). Your doctor will probably tell you not to take these medications if you are taking letermovir. Also tell your doctor if you are taking cyclosporine along with either simvastatin or pitavastatin. Your doctor will probably tell you not to take these combinations of medications with letermovir.
  • tell your doctor and pharmacist what other prescription and nonprescription medications, vitamins, nutritional supplements, and herbal products you are taking or plan to take. Be sure to mention any of the following: amiodarone (Nexterone, Pacerone); cyclosporine (Gengraf, Neoral, Sandimmune); fentanyl (Actiq, Duragesic, Subsys, others); glyburide (Diabeta, Glynase); HMG-CoA reductase inhibitors such as atorvastatin (Lipitor, in Caduet), fluvastatin (Lescol), lovastatin (Altoprev), pitavastatin (Livalo, Zypitamag), pravastatin (Pravachol), rosuvastatin (Crestor), and simvastatin (Flolipid, Zocor, in Vytorin); omeprazole (Prilosec, in Yosprala, Zegerid); pantoprazole (Protonix); phenytoin (Dilantin, Phenytek); sirolimus (Rapamune); quinidine (in Nuedexta); repaglinide (Prandin); rifampin (Rifadin, Rimactane, in Rfater, Rifamate), rosiglitazone (Avandia); tacrolimus (Astagraf, Envarsus, Prograf); voriconazole (Vfend); and warfarin (Coumadin, Jantoven). Your doctor may need to change the doses of your medications or monitor you carefully for side effects. Many other medications may also interact with letermovir, so be sure to tell your doctor about all the medications you are taking, even those that do not appear on this list.
  • tell your doctor if you have or have ever had kidney or liver disease.
  • tell your doctor if you are pregnant, plan to become pregnant, or are breastfeeding. If you become pregnant while taking letermovir, call your doctor.
  • if you are having surgery, including dental surgery, tell the doctor or dentist that you are taking letermovir.

Dosage Of Letermovir

Letermovir comes as a tablet to take by mouth. It is usually taken with or without food once a day. Your doctor will probably tell you to start taking letermovir after your receive the transplant and to stop taking the medication 100 days after the transplant. Take letermovir at around the same time every day. Follow the directions on your prescription label carefully, and ask your doctor or pharmacist to explain any part you do not understand. Take letermovir exactly as directed. Do not take more or less of it or take it more often than prescribed by your doctor.

Swallow the tablets whole; do not split, chew, or crush them.

Ask your pharmacist or doctor for a copy of the manufacturer’s information for the patient.


Keep all appointments with your doctor and the laboratory. Your doctor may order certain lab tests to check your body’s response to letermovir.

It is important for you to keep a written list of all of the prescription and nonprescription (over-the-counter) medicines you are taking, as well as any products such as vitamins, minerals, or other dietary supplements. You should bring this list with you each time you visit a doctor or if you are admitted to a hospital. It is also important information to carry with you in case of emergencies.


All information has been provided courtesy of MedLinePlus from the National Library of Medicine and from the FDA.