Taking phenytoin with other medicines and herbal supplements

Cautions with other medicines

There are lots of medicines that can affect phenytoin and increase the chances of you having side effects.

If you need to take these medicines, your doctor may change your dose of phenytoin.

Tell your doctor if you're taking:

• other medicines used to treat epilepsy, such as carbamazepine, clonazepam, lamotrigine, phenobarbital, sodium valproate, topiramate, oxcarbazepine, ethosuximide or vigabatrin
• medicines used to treat HIV
• hormonal contraceptives or hormone replacement therapy (HRT)
• medicines used for heart conditions and to help prevent blood clots like digoxin, amiodarone, furosemide, warfarin, diltiazem, nifedipine, apixaban or ticagrelor
• medicines used to treat fungal infections like fluconazole, itraconazole or miconazole
• medicines used for tuberculosis (TB) and other infections like isoniazid, rifampicin, sulfamethoxazole-trimethoprim, doxycycline or ciprofloxacin
• medicines used for stomach problems like omeprazole, sucralfate, ranitidine or some antacids
• theophylline, a medicine to help with breathing problems
• medicines used for sleeping problems (insomnia) and mental health problems like chlordiazepoxide, clozapine, clobazam, diazepam, disufiram, fluoxetine, quetiapine, trazodone or amitriptyline
• medicines used for transplants such as ciclosporin or tacrolimus
• medicines used for cancer
• bupropion, a medicine to help you stop smoking

This is not a full list of medicines that can affect phenytoin. For a full list, see the leaflet inside your medicines packet.

Mixing phenytoin with herbal remedies and supplements

There may be a problem taking some herbal remedies and supplements alongside phenytoin.

Do not take St John's wort with phenytoin, as it decreases the amount of phenytoin in your blood. If you already take it, talk to your doctor before stopping St John's wort as they may need to increase your phenytoin dose.

There's not enough information to say that other herbal remedies and supplements are safe to take with phenytoin. They're not tested in the same way as pharmacy and prescription medicines.