Drug interactions
Letermovir + Phenytoin
Severity: Major
Letermovir and Phenytoin: major interaction.
Last updated
For healthcare professionals — reference only. This page is a brief summary, not medical advice and not a substitute for official labeling or clinical judgement. Always verify before prescribing or dispensing.
Summary
Phenytoin can reduce letermovir exposure, potentially compromising CMV prophylaxis in transplant recipients. Letermovir may also lower phenytoin levels, which makes seizure control harder to predict.
What this interaction means in plain words
Letermovir and Phenytoin can interact in a way that may be serious. Using them together is sometimes necessary, but it needs a deliberate decision by the prescriber, a plan for monitoring, and clear advice on the warning signs to watch for.
Letermovir belongs to Anti Virals; Phenytoin belongs to Central Nervous System.
Why it happens
Phenytoin induces UGT enzymes and P-glycoprotein, increasing letermovir clearance and lowering absorption.
What to do
Avoid the combination and use a non-inducing antiseizure drug. If unavoidable, monitor phenytoin levels and CMV viral load.
What to ask your pharmacist
- Does the benefit of taking both outweigh the risk in my case?
- Do I need any blood test, ECG or other check while on both?
- What early warning signs should I watch for, and what should I do if they appear?
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Other interactions of Phenytoin
- Artemether / lumefantrine + Phenytoin Contraindicated
- Bictegravir + Phenytoin Contraindicated
- Cabotegravir + Phenytoin Contraindicated
- Doravirine + Phenytoin Contraindicated
- Elbasvir / grazoprevir + Phenytoin Contraindicated
- Elvitegravir / cobicistat / emtricitabine / tenofovir df + Phenytoin Contraindicated
Other interactions of Letermovir
- Ergotamine + Letermovir Contraindicated
- Letermovir + Pimozide Contraindicated
- Apalutamide + Letermovir Major
- Atorvastatin + Letermovir Major
- Carbamazepine + Letermovir Major
- Colchicine + Letermovir Major
Frequently asked questions
Can I take Letermovir with Phenytoin?
MediHelp rates the interaction as major. Letermovir and Phenytoin can interact in a way that may be serious. Using them together is sometimes necessary, but it needs a deliberate decision by the prescriber, a plan for monitoring, and clear advice on the warning signs to watch for. Phenytoin can reduce letermovir exposure, potentially compromising CMV prophylaxis in transplant recipients. Letermovir may also lower phenytoin levels, which makes seizure control harder to predict.
How serious is the interaction between Letermovir and Phenytoin?
MediHelp rates it major, on a four-level scale (minor, moderate, major, contraindicated) based on published labels and references. What to do, in brief: Avoid the combination and use a non-inducing antiseizure drug. If unavoidable, monitor phenytoin levels and CMV viral load.
What other medicines interact with Phenytoin?
MediHelp also lists interactions of Phenytoin with, for example, Artemether / lumefantrine, Bictegravir, Cabotegravir. The full list is on the Phenytoin page.
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