Gabapentin: discussion.

Gabapentin (GBP, Neurontin) is a novel antiepileptic drug (AED) that was shown to be effective against refractory partial seizures in five placebo-controlled trials. However, a number of patients with complex partial seizures experienced an increase in seizure frequency, suggesting that patients suffering from complex partial seizures are not a homogeneous group. In fact, we found that currently available AEDs are likely to be ineffective when staring is a prominent component of complex partial seizures. The poor response of this group of patients may reflect the fact that staring spells are inhibitory seizures and that the AEDs prescribed for partial seizures appear to facilitate inhibitory mechanisms. GBP resembles phenytoin (PHT) and carbamazepine (CBZ) in depressing segmental and reticular excitatory mechanisms and facilitating segmental inhibitory mechanisms, just as it resembles PHT and CBZ in efficacy against some partial seizures and against secondarily generalized seizures. Perhaps the patients in whom GBP increased seizure frequency had complex partial seizures with staring and were therefore unlikely to benefit from drugs such as GBP, CBZ, and PHT, which enhance inhibitory mechanisms in the brain. These findings suggest that future AED trials would greatly benefit from a categorization of complex partial seizures into nosologically distinct groups.