Drug interactions
Lamotrigine + Phenytoin
Severity: Moderate
Lamotrigine 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
Phenytoin substantially lowers lamotrigine concentrations, which can lead to loss of seizure control. Higher lamotrigine doses are usually needed, and stopping phenytoin later can cause lamotrigine levels to rise.
What this interaction means in plain words
Lamotrigine 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.
Lamotrigine belongs to Central Nervous System; Phenytoin belongs to Central Nervous System.
Why it happens
Phenytoin induces UGT-mediated glucuronidation of lamotrigine, increasing its clearance.
What to do
Use the enzyme-inducer dosing schedule for lamotrigine and monitor response. Reduce the lamotrigine dose if phenytoin is withdrawn.
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 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
Other interactions of Lamotrigine
Frequently asked questions
Can I take Lamotrigine with Phenytoin?
MediHelp rates the interaction as moderate. Lamotrigine 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. Phenytoin substantially lowers lamotrigine concentrations, which can lead to loss of seizure control. Higher lamotrigine doses are usually needed, and stopping phenytoin later can cause lamotrigine levels to rise.
How serious is the interaction between Lamotrigine 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: Use the enzyme-inducer dosing schedule for lamotrigine and monitor response. Reduce the lamotrigine dose if phenytoin is withdrawn.
What other medicines interact with Phenytoin?
MediHelp also lists interactions of Phenytoin with, for example, Artemether / lumefantrine, Bictegravir, Cabotegravir. The full list is on the Phenytoin page.
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