For most patients, treatment with a single antiepileptic drug (AED) offers many advantages:
One of the ways that adding an AED to an existing AED (i.e., changing a patient from monotherapy to polytherapy) may increase AED side effects is by raising serum levels of the first drug. For example, adding carbamazepine to phenytoin may increase mean total phenytoin serum levels by 35% and decrease phenytoin clearance by 37%. In other cases, the serum level of the first AED may be decreased, which could allow breakthrough seizures. See the (Table: AED-AED Interactions).
Combinations of AEDs and other types of medications may also cause side effects or breakthrough seizures. For example:
Reviewed and revised December 2003 by Steven C. Schachter, MD, Harvard Medical School
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