Drug interactions
Fosphenytoin + Lithium
Severity: Moderate
Fosphenytoin and Lithium: 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 has been reported with lithium toxicity symptoms, including neurologic effects, sometimes without elevated serum lithium concentrations. Evidence is limited to isolated reports.
What this interaction means in plain words
Fosphenytoin and Lithium 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; Lithium belongs to Central Nervous System.
Why it happens
Mechanism is not established; possible additive central neurotoxicity.
What to do
Monitor for tremor, ataxia, confusion and nystagmus, and check serum lithium and phenytoin levels if symptoms occur. Reduce doses if neurotoxicity appears.
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 Lithium
- Lithium + Thioridazine Contraindicated
- Lithium + Vandetanib Contraindicated
- Aceclofenac + Lithium Major
- Acemetacin + Lithium Major
- Amisulpride + Lithium Major
- Amlodipine-benazepril + Lithium 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 Lithium?
MediHelp rates the interaction as moderate. Fosphenytoin and Lithium 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 has been reported with lithium toxicity symptoms, including neurologic effects, sometimes without elevated serum lithium concentrations. Evidence is limited to isolated reports.
How serious is the interaction between Fosphenytoin and Lithium?
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 for tremor, ataxia, confusion and nystagmus, and check serum lithium and phenytoin levels if symptoms occur. Reduce doses if neurotoxicity appears.
What other medicines interact with Lithium?
MediHelp also lists interactions of Lithium with, for example, Thioridazine, Vandetanib, Aceclofenac. The full list is on the Lithium page.
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