Patients in Study C-024 (9) were randomized to vigabatrin 1 g/day (N = 92) or placebo (N = 90) at the first visit of the titration phase, and dosages were increased to 1.5 g/day at Week 2, 2 g/day at Week 3, and 2.5 g/day at Week 4). The j6 dosage was increased to 3 g/day at the beginning of the maintenance phase, and this dosage was maintained throughout the treatment period. In Study C-025 (10), patients were randomized to placebo (N = 45) or vigabatrin 1 g/day (N = 45), 3 g/day (N = 43), or 6 g/day (N = 41) during the 6-week titration period. There were no significant differences between treatment groups in baseline demographics, clinical characteristics, or concomitant AED medication for either Study C-024 (9) or C-025 (10). Patient disposition is provided in Table 4. Efficacy: primary endpoint —  In both studies, vigabatrin was superior to placebo for the primary efficacy endpoint — the change in median monthly frequency of CPS plus partial seizures secondarily generalized from baseline to the end of the study. In Study C-024 (9), median monthly frequency of seizures was decreased by 0.8 seizures in the placebo group vs 3.0 in the vigabatrin 1 g/day group (P = 0.0002; Fig. 2). In Study C-025 (10), median monthly frequency of seizures was decreased by 0.2 seizures in the placebo group vs 0.8 in the vigabatrin 1 g/day group (not significant), 4.3 in the 3 g/day group (P = 0.0001), and 4.5 in the 6 g/day group (P = 0.0001). A test for a linear trend across vigabatrin dosages in Study C-025 indicated an increased effect of vigabatrin with increasing dosage (P = 0.0001). However, 6 g/day was not statistically superior to 3 g/day. Efficacy: secondary endpoints —  Vigabatrin therapy was associated with a significantly greater responder rate (defined as ≥50% decrease in seizure frequency from baseline) than placebo (Table 5). In C-024 (9), the responder rate was 43% in the vigabatrin 3 g/d group vs 19% in the placebo group. In C-025 (10), the responder rate was 24%, 51%, and 54% in the vigabatrin 1, 3, and 6 g/day groups, respectively, vs 7% in the placebo group. Vigabatrin significantly increased the mean number of seizure-free days per month and number of patients who achieved seizure freedom at study end (Table 6) (9, 10). Results of the physician’s subjective evaluation of therapeutic effect were that 64% of the vigabatrin group (59 of 92 patients) and 30% of the placebo group (27 of 90 patients) demonstrated improvement during the study (P < 0.001) in Study C-024 (9). For this measure in Study C-025, there was a significant dosage-response relationship (P < 0.001) between increasing vigabatrin dosage and degree of improvement as demonstrated by moderate or better improvement in 32%, 40%, and 56% of patients in the vigabatrin 1, 3, and 6 g/day groups, respectively, compared with 20% of patients in the placebo group (10).