Efficacy and tolerability of adjunct perampanel based on number of antiepileptic drugs at baseline and baseline predictors of efficacy: A phase III post-hoc analysis

Perampanel is a selective, noncompetitive AMPA receptor antagonist with demonstrated efficacy and tolerability in partial seizures in patients aged ≥ 12 years in Phase III studies. Post-hoc analysis of these studies was conducted to determine the efficacy and tolerability of perampanel based on the number of concomitant antiepileptic drugs (AEDs) at baseline, as well as to examine which baseline characteristics, if any, were predictors of efficacy. Efficacy parameters were based on the number of baseline AEDs, and logistic regression analyses were used to evaluate the association of demographic and baseline clinical factors with probability of ≥ 50% reduction in seizure frequency. Patients on 1 AED at baseline were significantly more likely to have reduced seizure frequency (P<0.02) and improved 50% responder rate (P<0.02) than patients on 3 AEDs at baseline. Secondarily generalized seizures at baseline, unknown etiology, and use of concomitant non-inducer AEDs were also established as positive predictors of efficacy (50% responder rate; P<0.01). Patients with more AEDs at baseline were associated with greater use of inducers (P<0.01), which may result in decreased exposure of perampanel in these patients and lower efficacy. Patients with 1 AED at baseline had a significantly shorter time since diagnosis compared with patients in the 3 (P<0.01) AEDs group, as well as a lower median seizure frequency at baseline compared to patients on 3 AEDs (P<0.05), suggesting that the reduced efficacy of perampanel with 3 AEDs may also be associated with the greater severity of seizures in the patient groups. The incidence of adverse events in perampanel-treated patients was similar regardless of the number of AEDs at baseline. Greater efficacy is predicted for patients receiving fewer concomitant AEDs when starting perampanel, as well as for those receiving concomitant treatment with AEDs that are not CYP3A4 enzyme-inducers, compared to patients treated with multiple concomitant AEDs. The results of this study provide additional information for clinicians considering adding perampanel to their patients' treatment regimen earlier rather than later, and offer evidence regarding the potential for increased efficacy with a decreased medication burden.