Oxcarbazepine Drug Interactions: What to Avoid and What to Tell Your Doctor

Oxcarbazepine (Trileptal, Oxtellar XR) interacts with a number of other drugs, supplements, and substances. Some of these interactions reduce the effectiveness of other medications you're taking. Others raise or lower the levels of Oxcarbazepine in your blood. A few can be clinically significant. Here's what every patient on Oxcarbazepine needs to know.

How Oxcarbazepine Interacts With Other Drugs

Oxcarbazepine and its active metabolite (MHD) interact with the cytochrome P450 enzyme system in the liver — the same system that processes many common medications. Specifically:

• Oxcarbazepine is a weak inducer of CYP3A4 — this means it speeds up the breakdown of certain drugs that are metabolized by CYP3A4, potentially lowering their blood levels
• Oxcarbazepine is a weak inhibitor of CYP2C19 — this means it can slow the breakdown of drugs metabolized by this enzyme, potentially raising their levels

Major Interaction: Hormonal Contraceptives (Birth Control)

This is one of the most important interactions to know about. Oxcarbazepine reduces the plasma concentration of estrogen and progestin in hormonal contraceptives by inducing CYP3A4, which metabolizes hormonal contraceptives more quickly. This can significantly reduce the effectiveness of:

• Combined oral contraceptive pills ("the pill")
• Progestin-only pills ("mini pill")
• Hormonal patches and rings (e.g., NuvaRing)
• Implants and some hormonal IUDs (though non-hormonal IUDs like the copper IUD are NOT affected)

What to do: Use a non-hormonal backup contraceptive method (condoms, copper IUD) while taking Oxcarbazepine. Do not rely solely on hormonal contraception.

Other AEDs (Antiepileptic Drugs)

If you're on multiple seizure medications (as many epilepsy patients are), several important interactions exist:

• Phenytoin (Dilantin): At high Oxcarbazepine doses, MHD inhibits CYP2C19, which can increase phenytoin blood levels by up to 40%. Phenytoin levels should be monitored when adding or adjusting Oxcarbazepine.
• Carbamazepine, phenobarbital, phenytoin (as inducers): These drugs are strong CYP3A4 inducers and can reduce MHD blood levels by 25–49%. Higher Oxcarbazepine doses may be needed when combined with these drugs.
• Valproate (Depakote): May slightly increase MHD levels; generally a clinically minor interaction but worth monitoring.

CNS Depressants (Sedating Medications)

Combining Oxcarbazepine with other medications that cause drowsiness or sedation can amplify these effects significantly. Use caution with:

• Benzodiazepines (diazepam, lorazepam, clonazepam)
• Opioid pain medications
• Sleep aids (zolpidem, eszopiclone)
• Antihistamines (diphenhydramine, as in Benadryl)
• Alcohol

Medications That Lower Oxcarbazepine Levels

Some drugs speed up the breakdown of MHD, reducing its effectiveness:

• Rifampin (an antibiotic used for tuberculosis)
• Strong enzyme-inducing AEDs (carbamazepine, phenobarbital, phenytoin) — as noted above
• St. John's Wort (a herbal supplement) — can reduce levels of many medications including AEDs

Additional Interactions and Hyponatremia Risk

Diuretics (water pills) such as furosemide (Lasix), hydrochlorothiazide (HCTZ), and others increase the risk of hyponatremia (low sodium) when combined with Oxcarbazepine. If you take a diuretic, your doctor should monitor your sodium levels more frequently.

What to Tell Your Doctor

Before starting Oxcarbazepine — or before adding any new medication to your regimen — tell your prescriber about:

• All prescription and over-the-counter medications you take
• All herbal supplements (especially St. John's Wort)
• Your birth control method — so your doctor can recommend a backup
• Whether you take any diuretics or blood pressure medications
• Any Asian ancestry (for HLA-B*1502 screening before starting)

For a complete overview of Oxcarbazepine side effects and warning signs to watch for, see our guide on Oxcarbazepine side effects.