Lamotrigine is a chemically novel
antiepileptic drug which has not been adequately assessed for its antineuralgic properties. It was used in a double-blind placebo controlled crossover trial in 14 patients with refractory
trigeminal neuralgia. Patients continued to take a steady dose of
carbamazepine or
phenytoin throughout the trial over a 31-day period. Each arm of the trial lasted 2 weeks with an intervening 3-day washout period. The maintenance dose of
lamotrigine was 400 mg.
Lamotrigine was superior to placebo (P = 0.011) based on analysis of a composite efficacy index which compared the numbers of patients assigned greater efficacy on
lamotrigine with those assigned greater efficacy on placebo. Efficacy for one treatment over another was determined according to a hierarchy of: (i) use of escape medication; (ii) total
pain scores; or (iii) global evaluations. Eleven of the 13 patients eligible for inclusion in the composite efficacy index showed better efficacy on
lamotrigine compared with placebo. Global evaluations further suggested that patients did better on
lamotrigine than placebo (P = 0.025). The adverse reactions with both
lamotrigine and placebo were predominantly dose-dependent effects on the central nervous system. A 14th patient withdrew from the study due to severe
pain during the placebo arm of the trial. It would appear that
lamotrigine has antineuralgic properties.