Does Phenytoin Interact with Lamotrigine Extended Release?
Phenytoin and Lamotrigine Extended Release have a moderate drug interaction according to U.S. FDA drug labeling data. Decreases lamotrigine concentration approximately 40%. The mechanism involves induces lamotrigine glucuronidation. Patients taking both medications should consult their healthcare provider before starting, stopping, or changing the dosage of either drug. This information is based on official FDA drug labeling sourced from OpenFDA and the NIH National Library of Medicine.
- Severity
- Moderate
- Phenytoin Class
- Anti-epileptic Agent
- Lamotrigine Extended Release Class
- Anti-epileptic Agent
- Management
- Monitor for effects
- Data Source
- U.S. FDA via OpenFDA
How This Interaction Works
The interaction between Phenytoin and Lamotrigine Extended Release occurs because induces lamotrigine glucuronidation. Clinically, this means decreases lamotrigine concentration approximately 40%. This is classified as a moderate interaction. While it may not require stopping either medication, your healthcare provider should be aware you are taking both so they can monitor for potential effects and adjust treatment if necessary.
What To Tell Your Doctor or Pharmacist
If you are taking Phenytoin and your doctor is considering prescribing Lamotrigine Extended Release (or vice versa), make sure to:
- Inform your doctor and pharmacist of all current medications, including over-the-counter drugs and supplements
- Ask whether the benefits of combining these medications outweigh the risks for your specific situation
- Ask what symptoms to watch for that would indicate the interaction is causing problems
- Ask whether any dosage adjustments are needed
- Never stop or change either medication without first consulting your healthcare provider