Drug interactions
Fosphenytoin + Mefloquine
Severity: Moderate
Fosphenytoin and Mefloquine: moderate 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
Mefloquine can lower the seizure threshold and may reduce the effectiveness of anticonvulsants such as fosphenytoin. Fosphenytoin does not clearly prolong QT, so the concern is mainly loss of seizure control. Phenytoin is also a CYP3A4 inducer and may lower mefloquine levels.
What this interaction means in plain words
Fosphenytoin and Mefloquine can affect each other. The combination is often manageable, but it may need a change of dose, a change of timing, or extra checks while both are taken.
Fosphenytoin belongs to Central Nervous System; Mefloquine belongs to Anti Parasitic.
Why it happens
Mefloquine is proconvulsant, and phenytoin induces CYP3A4, which may lower mefloquine exposure.
What to do
Avoid mefloquine in patients with epilepsy where possible. If used, monitor seizure control, phenytoin levels and mefloquine efficacy.
What to ask your pharmacist
- Should I take them at different times of day?
- Does the dose of either medicine need to change?
- Is there anything I should avoid, such as alcohol or certain foods, while on both?
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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 Fosphenytoin
- Dronedarone + Fosphenytoin Contraindicated
- Fosphenytoin + Ledipasvir-sofosbuvir Contraindicated
- Fosphenytoin + Lorlatinib Contraindicated
- Fosphenytoin + Lurasidone Contraindicated
- Fosphenytoin + Ranolazine Contraindicated
- Fosphenytoin + Sofosbuvir-velpatasvir-voxilaprevir Contraindicated
Frequently asked questions
Can I take Fosphenytoin with Mefloquine?
MediHelp rates the interaction as moderate. Fosphenytoin and Mefloquine can affect each other. The combination is often manageable, but it may need a change of dose, a change of timing, or extra checks while both are taken. Mefloquine can lower the seizure threshold and may reduce the effectiveness of anticonvulsants such as fosphenytoin. Fosphenytoin does not clearly prolong QT, so the concern is mainly loss of seizure control. Phenytoin is also a CYP3A4 inducer and may lower mefloquine levels.
How serious is the interaction between Fosphenytoin and Mefloquine?
MediHelp rates it moderate, on a four-level scale (minor, moderate, major, contraindicated) based on published labels and references. What to do, in brief: Avoid mefloquine in patients with epilepsy where possible. If used, monitor seizure control, phenytoin levels and mefloquine efficacy.
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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