The efficacy of dichlorphenamide tablets was evaluated in two clinical studies, Study 1 and Study 2.

Study 1

Study 1 was a 9-week, double-blind, placebo-controlled multi-center study. Study 1 consisted of two substudies: a substudy in patients with hypokalemic periodic paralysis (n=44), and a substudy in patients with hyperkalemic periodic paralysis (n=21). The primary efficacy endpoint in both substudies was the average number of self-reported attacks of muscle weakness per week over the final 8 weeks of the trial. Withdrawal from the study for acute severe worsening (increase in attack frequency or severity) was also assessed as an endpoint.

In Study 1, the dose of dichlorphenamide tablets was 50 mg b.i.d. for treatment-naïve patients. Patients already on dichlorphenamide prior to the study continued on the same dose while on dichlorphenamide during the study. In patients taking acetazolamide prior to the study, the dose of dichlorphenamide was set at 20% of the acetazolamide dose. Dose reduction for tolerability was permitted.

Hypokalemic Periodic Paralysis Substudy of Study 1

In the hypokalemic periodic paralysis substudy, median age of patients was 45 years and 73% of patients were male. Patients treated with dichlorphenamide (n=24) had 2.2 fewer attacks per week than patients (n=20) treated with placebo (p=0.02). None of the patients randomized to dichlorphenamide reached the endpoint of withdrawal from the study for acute worsening, vs. five patients randomized to placebo. The mean dose of dichlorphenamide at Week 9 was 94 mg/day.

Hyperkalemic Periodic Paralysis Substudy of Study 1

In the Hyperkalemic Periodic Paralysis substudy, median age of patients was 43 years and 43% of patients were male. During the double-blind treatment period, patients treated with dichlorphenamide (n=12) had 3.9 fewer attacks per week than patients (n=9) treated with placebo (p=0.08). None of the patients randomized to dichlorphenamide reached the endpoint of withdrawal from the study for acute worsening, vs. two patients randomized to placebo. The mean dose of dichlorphenamide at Week 9 was 82 mg/day.

Study 2

Study 2 was a 35-week, double-blind, placebo-controlled, multi-center, two-period crossover study. Study 2 also consisted of two substudies: a substudy in patients with hypokalemic periodic paralysis (n=42), and a substudy in patients with hyperkalemic periodic paralysis (n=31), including patients with Paramyotonia Congenita. The primary endpoint in the hypokalemic periodic paralysis substudy was the incidence of acute intolerable worsening (based on attack frequency or severity) necessitating withdrawal. The primary endpoint in the hyperkalemic periodic paralysis substudy was the average number of self-reported attacks of muscle weakness per week. Dosing was determined similarly to Study 1.

Hypokalemic Periodic Paralysis Substudy of Study 2

The hypokalemic periodic paralysis substudy included patients with a mean age of 38 years; 79% of patients were male. Acute intolerable worsening was observed in 2 patients on dichlorphenamide vs. 11 patients on placebo (p=0.02). The mean dose of dichlorphenamide at the end of the study was 96 mg/day.

Hyperkalemic Periodic Paralysis Substudy of Study 2

The hyperkalemic periodic paralysis substudy included patients with a mean age of 37 years; and 79% of patients were male. Patients treated had 2.3 fewer attacks per week on dichlorphenamide than on placebo (p=0.006). The mean dose of dichlorphenamide at the end of the study was 73 mg/day.