Does Levothyroxine Sodium Interact with Phenytoin?
Levothyroxine Sodium and Phenytoin have a moderate drug interaction according to U.S. FDA drug labeling data. Reduces serum protein binding of levothyroxine; total and free T4 may be reduced 20-40%, though most patients remain euthyroid. Closely monitor thyroid parameters. The mechanism involves reduces serum protein binding of levothyroxine. 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
- Management
- Monitor for effects
- Data Source
- U.S. FDA via OpenFDA
How This Interaction Works
The interaction between Levothyroxine Sodium and Phenytoin occurs because reduces serum protein binding of levothyroxine. Clinically, this means reduces serum protein binding of levothyroxine; total and free t4 may be reduced 20-40%, though most patients remain euthyroid. closely monitor thyroid parameters. 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 Levothyroxine Sodium and your doctor is considering prescribing Phenytoin (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