Adjunctive therapy in epilepsy: a cost-effectiveness comparison of two AEDs.

The objective of this study was to compare the relative cost-effectiveness of two AEDs by a prospective clinical audit. Patients starting on the adjunctive therapies lamotrigine and topiramate were recruited from the out-patient epilepsy clinics at Queen Square. Three interview were scheduled: baseline; three months follow-up and six months from baseline. Of the 81 patients recruited, a total of 73 patients completed all three interviews. An intention to treat analysis was performed on the data. Seizure severity and frequency were assessed using the National Hospital Seizure Severity Scale. Side-effects, adverse events and reasons for stopping medication were also recorded. At the third interview, a total of 47/73 (64%) were still on the prescribed adjunctive drug. Outcome was assessed by two methods: the > 50% seizure reduction cited in the literature and a more stringent assessment of patient 'satisfaction' which we defined operationally on clinical criteria. Using this definition, a total of 10/73 (14%) patients were 'satisfied'. The relative costs of starting patients on each of the two AEDs were calculated, both drug costs and the costs of adverse events (the latter were defined as events requiring urgent medical attention). The costs of the two drugs were compared. A number of methodological issues relating to cost comparison are discussed. Outcome and pharmaco-economic studies need to assess more than reduction in number of seizures. They should take into account variables important for quality of life including side-effects and adverse events.