Behavioural abnormalities and retention rates of anti-epilepsy drugs during long-term treatment of epilepsy: a clinical perspective.

Vigabatrin is among the most promising of the new anti-epilepsy drugs, but two unrelated complications have been noted in patients receiving vigabatrin for chronic refractory epilepsy. These are, transient behavioural abnormalities and falling numbers of patients continuing to take vigabatrin (decreasing retention rate) during long-term treatment. Psychotic reactions have been carefully documented both in patients receiving standard and new anti-epilepsy drugs, and in up to 6% of patients after epilepsy surgery. As many psychotic episodes are associated with a dramatic cessation of seizures (i.e. high efficacy of treatment), it is not surprising that behavioural abnormalities are more often seen in patients receiving higher, more effective doses of vigabatrin, particularly those taking more than 3 g/day. A gradual dose increase and slow withdrawal is recommended for possible prevention of behavioural abnormalities, at least in some patients. During treatment with standard anti-epilepsy drugs, approximately 50% of patients remain on randomized treatment with the same drug for several years. For oxcarbazepine, a new drug, the figure is 60%, and for vigabatrin it is about 50%. Although comparative trials are not available, the retention rate for vigabatrin does not appear to be strikingly different to that reported for conventional anti-epilepsy drugs. In summary, behavioural abnormalities and falling retention rates appear to be general features of chronic epilepsy, and are certainly not exclusively associated with the use of vigabatrin. Controlled trials are required to establish the specific contribution, if any, of vigabatrin in development of these complications of intractable epilepsy.