Drug interactions
Mefloquine + Phenytoin
Severity: Major
Mefloquine 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 induces CYP3A4 and may lower mefloquine concentrations, reducing prophylactic or treatment efficacy. Mefloquine can also lower the seizure threshold and may reduce seizure control in people with epilepsy.
What this interaction means in plain words
Mefloquine 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.
Mefloquine belongs to Anti Parasitic; Phenytoin belongs to Central Nervous System.
Why it happens
Induction of CYP3A4-mediated mefloquine metabolism by phenytoin, plus a pharmacodynamic proconvulsant effect of mefloquine.
What to do
Avoid mefloquine in patients taking phenytoin and choose another antimalarial. If used, monitor seizure control and phenytoin levels.
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 Mefloquine
- Arsenic trioxide + Mefloquine Contraindicated
- Dronedarone + Mefloquine Contraindicated
- Ibutilide + Mefloquine Contraindicated
- Levoketoconazole + Mefloquine Contraindicated
- Mefloquine + Nilotinib Contraindicated
- Mefloquine + Pimozide Contraindicated
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
Frequently asked questions
Can I take Mefloquine with Phenytoin?
MediHelp rates the interaction as major. Mefloquine 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 induces CYP3A4 and may lower mefloquine concentrations, reducing prophylactic or treatment efficacy. Mefloquine can also lower the seizure threshold and may reduce seizure control in people with epilepsy.
How serious is the interaction between Mefloquine 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 mefloquine in patients taking phenytoin and choose another antimalarial. If used, monitor seizure control and phenytoin levels.
What other medicines interact with Mefloquine?
MediHelp also lists interactions of Mefloquine with, for example, Arsenic trioxide, Dronedarone, Ibutilide. The full list is on the Mefloquine page.
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