Letermovir belongs to the class of medications called antivirals. It is used to prevent infection caused by cytomegalovirus (CMV) for adults who have had a stem cell transplant with cells from another person, who are at risk of developing CMV infection.

Letermovir works by preventing CMV from reproducing and spreading, causing infection.

Prevymis may be available under multiple brand names and/or in several different forms. Any specific brand name of Prevymis may not be available in all of the forms or approved for all of the conditions discussed here. As well, some forms of Prevymis may not be used for all of the conditions discussed here.

Your doctor may have suggested Prevymis for conditions other than those listed in these drug information articles. If you have not discussed this with your doctor or are not sure why you are taking Prevymis, speak to your doctor. Do not stop taking Prevymis without consulting your doctor.

Do not give Prevymis to anyone else, even if they have the same symptoms as you do. It can be harmful for people to take Prevymis if their doctor has not prescribed it.

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There are two forms of Prevymis: tablets and solution for intravenous (into a vein) infusion.

The recommended adult dose of letermovir is 480 mg taken by mouth, once daily. It should be started on or after the day you receive the stem cell transplant, but no later than 28 days after the transplant. It is generally taken until 100 days after the transplant.

The tablets should be taken at approximately the same time each day. Swallow the tablets whole with some fluid. Do not crush or chew the tablets. Letermovir may be taken with food or on an empty stomach.

If you are receiving the intravenous form of Prevymis, it will take approximately 1 hour for the infusion to complete.

Many things can affect the dose of medication that a person needs, such as body weight, other medical conditions, and other medications. If your doctor has recommended a dose different from the ones listed here, do not change the way that you are taking the medication without consulting your doctor.

It is important to take Prevymis exactly as prescribed by your doctor.

If you miss a dose, take it as soon as possible and continue with your regular schedule. If it is almost time for your next dose, skip the missed dose and continue with your regular dosing schedule. Do not take a double dose to make up for a missed one. If you are not sure what to do after missing a dose, contact your doctor or pharmacist for advice.

Store Prevymis in its original package at room temperature, protect it from light and moisture, and keep it out of the reach of children.

Do not dispose of medications in wastewater (e.g. down the sink or in the toilet) or in household garbage. Ask your pharmacist how to dispose of medications that are no longer needed or have expired.

Many medications can cause side effects. A side effect is an unwanted response to a medication when it is taken in normal doses. Side effects can be mild or severe, temporary or permanent.

The side effects listed below are not experienced by everyone who takes Prevymis. If you are concerned about side effects, discuss the risks and benefits of Prevymis with your doctor.

The following side effects have been reported by at least 1% of people taking Prevymis. Many of these side effects can be managed, and some may go away on their own over time.

Contact your doctor if you experience these side effects and they are severe or bothersome. Your pharmacist may be able to advise you on managing side effects.

• Diarrhea
• nausea
• vomiting

Although most of the side effects listed below don't happen very often, they could lead to serious problems if you do not seek medical attention.

Check with your doctor as soon as possible if any of the following side effects occur:

• rapid heartbeat
• symptoms of irregular heartbeat (e.g., chest pain, dizziness, rapid, pounding heartbeat, shortness of breath)

Stop taking the medication and seek immediate medical attention if any of the following occur:

• signs of a serious allergic reaction (e.g., abdominal cramps, difficulty breathing, nausea and vomiting, or swelling of the face and throat)

Some people may experience side effects other than those listed. Check with your doctor if you notice any symptom that worries you while you are taking Prevymis.

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Tablets

240 mg
Each yellow oval tablet, debossed with "591" on one side and the Merck logo on the other side contains 240 mg of letermovir. Nonmedicinal ingredients: colloidal silicon dioxide, croscarmellose sodium, magnesium stearate, microcrystalline cellulose and povidone 25; film-coating: hypromellose 2910, iron oxide yellow, lactose monohydrate, titanium dioxide, triacetin, and carnauba wax.

480 mg
Each pink, oval, bi-convex tablet, debossed with "595" on one side and the Merck logo on the other side, contains 480 mg of letermovir. Nonmedicinal ingredients: colloidal silicon dioxide, croscarmellose sodium, magnesium stearate, microcrystalline cellulose and povidone 25; film-coating: hypromellose 2910, iron oxide yellow, iron oxide red, lactose monohydrate, titanium dioxide, triacetin, and carnauba wax.

Solution for Injection

Each mL of clear, preservative-free sterile solution in single dose vials of either 240 mg or 480 mg per vial, contains 20 mg of letermovir. Nonmedicinal ingredients: hydroxypropyl betadex, sodium chloride, sodium hydroxide and water for injection. The amount of sodium hydroxide may be adjusted to achieve a pH of approximately 7.5.

Do not take Prevymis if you:

• are allergic to letermovir or any ingredients of the medication
• are taking the medication Pimozide
• are taking ergotamine or Dihydroergotamine for migraines

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There may be an interaction between letermovir and any of the following:

• alpha blockers (e.g., Alfuzosin, Doxazosin, Silodosin, Tamsulosin)
• antiarrythmics (e.g., Amiodarone, Disopyramide, dofetilide, quinidine)
• anti-cancer medications (e.g., Cabazitaxel, Docetaxel, Doxorubicin; Etoposide, Ifosfamide, Irinotecan, Vincristine)
• antipsychotics (e.g., Aripiprazole, Clozapine, Haloperidol, Olanzapine, pimozide, Quetiapine, Risperidone)
• Apixaban
• Aprepitant
• "azole" antifungals (e.g., itraconazole, ketoconazole, Voriconazole)
• benzodiazepines (e.g., Chlordiazepoxide, Clonazepam, Diazepam, Lorazepam)
• Bosentan
• Bromocriptine
• Buspirone
• Calcitriol
• calcium channel blockers (e.g., Amlodipine, Diltiazem, Nifedipine, Verapamil)
• cannabis
• chloroquine
• Colchicine
• conivaptan
• corticosteroids (e.g., budesonide, Dexamethasone)
• Cyclosporine
• Dapsone
• Darifenacin
• Domperidone
• Eletriptan
• Eltrombopag
• Eplerenone
• ergot alkaloids (e.g., dihydroergotamine, ergonovine, ergotamine, methylergonovine)
• Everolimus
• Gemfibrozil
• "gliptin" Diabetes medications (e.g., Linagliptin, Saxagliptin, Sitagliptin)
• Glyburide
• Guanfacine
• Hepatitis C antivirals (e.g., asunaprevir, daclatasvir, grazoprevir, simeprevir)
• HIV non-nucleoside reverse transcriptase inhibitors (NNRTIs; e.g., delaviridine, efavirenz, etravirine, nevirapine)
• HIV protease inhibitors (e.g., atazanavir, indinavir, ritonavir, saquinavir)
• Hydroxyzine
• Ivacaftor
• lidocaine
• Lomitapide
• macrolide antibiotics (e.g., clarithromycin, erythromycin)
• maraviroc
• Mefloquine
• Methadone
• mifepristone
• Mirtazapine
• Naloxegol
• narcotic pain relievers (e.g., Fentanyl, Hydrocodone, Oxycodone)
• nefazodone
• nitrates (e.g., isosorbide dinitrate, isosorbide mononitrate)
• Pimecrolimus
• protein kinase inhbitors (e.g., Bosutinib, imatinib, Lapatinib, Nilotinib, Pazopanib
• quinine
• Repaglinide
• rifabutin
• rifampin
• Rosiglitazone
• salmeterol
• saxagliptin
• seizure medications (e.g., Carbamazepine, Clobazam, Levetiracetam, Phenobarbital, Phenytoin, primidone, Topiramate, Valproic acid, zonisamide)
• selective serotonin reuptake inhibitors (SSRIs; e.g., Citalopram, , Fluoxetine, Paroxetine, Sertraline)
• Sildenafil
• "statin" anti-cholesterol medications (e.g., Atorvastatin, Lovastatin, Simvastatin)
• Sirolimus
• Tacrolimus
• Tamoxifen
• tamsulosin
• Teriflunomide
• Ticagrelor
• Tolterodine
• Tolvaptan
• Trazodone
• tricyclic antidepressants (e.g., Amitriptyline, Clomipramine, Desipramine, Trimipramine)
• Ulipristal
• Venlafaxine
• Warfarin
• Zopiclone

If you are taking any of these medications, speak with your doctor or pharmacist. Depending on your specific circumstances, your doctor may want you to:

• stop taking one of the medications,
• change one of the medications to another,
• change how you are taking one or both of the medications, or
• leave everything as is.

An interaction between two medications does not always mean that you must stop taking one of them. Speak to your doctor about how any drug interactions are being managed or should be managed.

Medications other than those listed above may interact with Prevymis. Tell your doctor or prescriber about all prescription, over-the-counter (non-prescription), and herbal medications you are taking. Also tell them about any supplements you take. Since caffeine, alcohol, the Nicotine from cigarettes, or street drugs can affect the action of many medications, you should let your prescriber know if you use them.

Before you begin using a medication, be sure to inform your doctor of any medical conditions or Allergies you may have, any medications you are taking, whether you are pregnant or breast-feeding, and any other significant facts about your health. These factors may affect how you should use Prevymis.

Kidney function: Decreased kidney function or Kidney Disease may cause Prevymis to build up in your body, causing side effects. If you have kidney problems, discuss with your doctor how Prevymis may affect your medical condition, how your medical condition may affect the dosing and effectiveness of Prevymis, and whether any special monitoring is needed.

Liver function: Decreased liver function or liver disease may cause Prevymis to build up in your body, causing side effects. If you have liver problems, discuss with your doctor how Prevymis may affect your medical condition, how your medical condition may affect the dosing and effectiveness of Prevymis, and whether any special monitoring is needed.

Pregnancy: Prevymis should not be used during pregnancy unless the benefits outweigh the risks. If you become pregnant while taking Prevymis, contact your doctor immediately.

Breast-feeding: It is not known if letermovir passes into breast milk. If you are a breast-feeding mother and are taking Prevymis, it may affect your baby. Talk to your doctor about whether you should continue breast-feeding.

Children: The safety and effectiveness of using Prevymis have not been established for children.

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