Drug interactions
Fosphenytoin + Mexiletine
Severity: Moderate
Fosphenytoin and Mexiletine: 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
Fosphenytoin is converted to phenytoin, a recognized enzyme inducer that lowers mexiletine concentrations. This can lead to reduced antiarrhythmic or analgesic effect.
What this interaction means in plain words
Fosphenytoin and Mexiletine 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; Mexiletine belongs to Cardiovascular.
Why it happens
Phenytoin induces hepatic enzymes (including CYP1A2 and CYP2D6) increasing mexiletine clearance.
What to do
Monitor clinical response and mexiletine levels, and raise the dose if needed. Reassess the dose when fosphenytoin is discontinued.
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 Mexiletine
- Fezolinetant + Mexiletine Contraindicated
- Mexiletine + Pimozide Contraindicated
- Alosetron + Mexiletine Major
- Amiodarone + Mexiletine Major
- Clozapine + Mexiletine Major
- Cobicistat + Mexiletine Major
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 Mexiletine?
MediHelp rates the interaction as moderate. Fosphenytoin and Mexiletine 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 is converted to phenytoin, a recognized enzyme inducer that lowers mexiletine concentrations. This can lead to reduced antiarrhythmic or analgesic effect.
How serious is the interaction between Fosphenytoin and Mexiletine?
MediHelp rates it moderate, on a four-level scale (minor, moderate, major, contraindicated) based on published labels and references. What to do, in brief: Monitor clinical response and mexiletine levels, and raise the dose if needed. Reassess the dose when fosphenytoin is discontinued.
What other medicines interact with Mexiletine?
MediHelp also lists interactions of Mexiletine with, for example, Fezolinetant, Pimozide, Alosetron. The full list is on the Mexiletine page.
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