Drug interactions
Fosphenytoin + Meperidine
Severity: Moderate
Fosphenytoin and Meperidine: 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
Phenytoin, the active form of fosphenytoin, induces hepatic enzymes and has been shown to reduce meperidine levels while increasing normeperidine, a metabolite that can cause CNS excitation and seizures. This may reduce analgesia and raise neurotoxicity risk.
What this interaction means in plain words
Fosphenytoin and Meperidine 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; Meperidine belongs to Musculoskeletal.
Why it happens
Induction of hepatic CYP enzymes by phenytoin increases meperidine N-demethylation to normeperidine.
What to do
Prefer an alternative opioid in patients on phenytoin. If meperidine is used, keep the course short and monitor for tremor, myoclonus and seizures.
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 Meperidine
- Alvimopan + Meperidine Contraindicated
- Isocarboxazid + Meperidine Contraindicated
- Meperidine + Methylene blue Contraindicated
- Meperidine + Olanzapine / samidorphan Contraindicated
- Meperidine + Phenelzine Contraindicated
- Meperidine + Procarbazine 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 Meperidine?
MediHelp rates the interaction as moderate. Fosphenytoin and Meperidine 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. Phenytoin, the active form of fosphenytoin, induces hepatic enzymes and has been shown to reduce meperidine levels while increasing normeperidine, a metabolite that can cause CNS excitation and seizures. This may reduce analgesia and raise neurotoxicity risk.
How serious is the interaction between Fosphenytoin and Meperidine?
MediHelp rates it moderate, on a four-level scale (minor, moderate, major, contraindicated) based on published labels and references. What to do, in brief: Prefer an alternative opioid in patients on phenytoin. If meperidine is used, keep the course short and monitor for tremor, myoclonus and seizures.
What other medicines interact with Meperidine?
MediHelp also lists interactions of Meperidine with, for example, Alvimopan, Isocarboxazid, Methylene blue. The full list is on the Meperidine page.
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