Drug interactions
Lithium + Phenytoin
Severity: Moderate
Lithium and Phenytoin: 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
Neurotoxicity has been reported when lithium is combined with phenytoin, sometimes with lithium levels in the usual range. The evidence consists of isolated case reports, but features such as ataxia, tremor and confusion can be significant.
What this interaction means in plain words
Lithium and Phenytoin 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.
Lithium belongs to Central Nervous System; Phenytoin belongs to Central Nervous System.
Why it happens
Mechanism is not established; possible additive neurotoxic effects.
What to do
Monitor for neurological symptoms and serum lithium and phenytoin levels when starting or changing either drug. Reduce or stop the drugs 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 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 Lithium with Phenytoin?
MediHelp rates the interaction as moderate. Lithium and Phenytoin 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. Neurotoxicity has been reported when lithium is combined with phenytoin, sometimes with lithium levels in the usual range. The evidence consists of isolated case reports, but features such as ataxia, tremor and confusion can be significant.
How serious is the interaction between Lithium and Phenytoin?
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 neurological symptoms and serum lithium and phenytoin levels when starting or changing either drug. Reduce or stop the drugs 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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