How the interaction occurs:
Some anticonvulsants such as carbamazepine, phenytoin, phenobarbital, and primidone may increase how quickly your liver processes lamotrigine.
What might happen:
The amount of lamotrigine in your blood may decrease. It may not prevent seizures as well.
What you should do about this interaction:
These medicines are often used together to control seizures. Let your healthcare professionals (e.g. doctor or pharmacist) know that you are taking these medicines together. If you are starting lamotrigine, your doctor may titrate your dose of lamotrigine differently because you are on another medicine. If your doctor instructs you to stop taking one of your other anticonvulsant medicines, your doctor may want to change the dose of your lamotrigine. If you have a seizure, contact your doctor right away.Your healthcare professionals may already be aware of this interaction and may be monitoring you for it. Do not start, stop, or change the dosage of any medicine before checking with them first.
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3.Grasela TH, Fiedler-Kelly J, Cox E, Womble GP, Risner ME, Chen C. Population pharmacokinetics of lamotrigine adjunctive therapy in adults with epilepsy. J Clin Pharmacol 1999 Apr;39(4):373-84.