Starting antiepileptic drug therapy

Most antiepileptic drugs are started at a low dose, which is slowly increased to the initial target. This is especially important for lamotrigine, to reduce the risk of serious adverse skin reactions. An exception is phenytoin, which can be started at the initial target dose or even with a loading dose.

Antiepileptic therapy should start with a single drug. The initial target is the dose likely to be effective, based on the drug's effective dose range (or, for phenytoin, serum concentration). If seizures continue, the dose is increased until seizures stop or the maximum dose is reached. The maximum dose depends on the patient and the drug, and is decided in one of three ways—it is the dose that:

• is slightly less than the dose that has produced dose-related toxicity
• if exceeded, is likely to produce dose-related toxicity or is unlikely to achieve further efficacy
• results in a serum concentration near the upper limit of the target range (for phenytoin).