The efficacy of MIRAPEX tablets in the treatment of Restless Legs Syndrome (RLS) was evaluated in a multinational drug development program consisting of 4 randomized, double-blind, placebo-controlled trials. This program included approximately 1000 patients with moderate to severe RLS; patients with RLS secondary to other conditions (e.g., pregnancy, renal failure, and anemia) were excluded. All patients were administered MIRAPEX tablets (0.125 mg, 0.25 mg, 0.5 mg, or 0.75 mg) or placebo once daily 2-3 hours before going to bed. Across the 4 studies, the mean duration of RLS was 4.6 years (range of 0 to 56 years), mean age was approximately 55 years (range of 18 to 81 years), and approximately 66.6% were women.

The two outcome measures used to assess the effect of treatment were the International RLS Rating Scale (IRLS Scale) and a Clinical Global Impression - Improvement (CGI-I) assessment. The IRLS Scale contains 10 items designed to assess the severity of sensory and motor symptoms, sleep disturbance, daytime somnolence, and impact on activities of daily living and mood associated with RLS. The range of scores is 0 to 40, with 0 being absence of RLS symptoms and 40 the most severe symptoms. The CGI-I is designed to assess clinical progress (global improvement) on a 7-point scale. 

In Study 1, fixed doses of MIRAPEX tablets were compared to placebo in a study of 12 weeks duration. A total of 344 patients were randomized equally to the 4 treatment groups. Patients treated with MIRAPEX tablets (n=254) had a starting dose of 0.125 mg/day and were titrated to one of the three randomized doses (0.25, 0.5, 0.75 mg/day) in the first three weeks of the study. The mean improvement from baseline on the IRLS Scale total score and the percentage of CGI-I responders for each of the MIRAPEX tablets treatment groups compared to placebo are summarized in Table 1. All treatment groups reached statistically significant superiority compared to placebo for both endpoints. There was no clear evidence of a dose-response across the 3 randomized dose groups.

Study 2 was a randomized-withdrawal study, designed to demonstrate the sustained efficacy of pramipexole for treatment of RLS after a period of six months. RLS patients who responded to Mirapex® (pramipexole dihydrochloride) tablets treatment in a preceding 6-month open label treatment phase (defined as having a CGI-I rating of “very much improved” or “much improved” compared to baseline and an IRLS score of 15 or below) were randomized to receive either continued active treatment (n=78) or placebo (n=69) for 12 weeks. The primary endpoint of this study was time to treatment failure, defined as any worsening on the CGI-I score along with an IRLS Scale total score above 15. 

In patients who had responded to 6-month open label treatment with MIRAPEX tablets, the administration of placebo led to a rapid decline in their overall conditions and return of their RLS symptoms. At the end of the 12-week observation period, 85% of patients treated with placebo had failed treatment, compared to 21% treated with blinded pramipexole, a difference that was highly statistically significant. The majority of treatment failures occurred within 10 days of randomization. For the patients randomized, the distribution of doses was: 7 on 0.125 mg, 44 on 0.25 mg, 47 on 0.5 mg, and 49 on 0.75 mg.

Study 3 was a 6-week study, comparing a flexible dose of MIRAPEX tablets to placebo. In this study, 345 patients were randomized in a 2:1 ratio to MIRAPEX tablets or placebo. The mean improvement from baseline on the IRLS Scale total score was -12 for Mirapex-treated patients and -6 for placebo-treated patients. The percentage of CGI-I responders was 63% for Mirapex-treated patients and 32% for placebo-treated patients. The between-group differences were statistically significant for both outcome measures. For the patients randomized to MIRAPEX tablets, the distribution of achieved doses was: 35 on 0.125 mg, 51 on 0.25 mg, 65 on 0.5 mg, and 69 on 0.75 mg.

Study 4 was a 3-week study, comparing 4 fixed doses of MIRAPEX tablets, 0.125 mg, 0.25 mg, 0.5 mg, and 0.75 mg, to placebo. Approximately 20 patients were randomized to each of the 5 dose groups. The mean improvement from baseline on the IRLS Scale total score and the percentage of CGI-I responders for each of the MIRAPEX tablets treatment groups compared to placebo are summarized in Table 2. In this study, the 0.125 mg dose group was not significantly different from placebo. On average, the 0.5 mg dose group performed better than the 0.25 mg dose group, but there was no difference between the 0.5 mg and 0.75 mg dose groups. 

No differences in effectiveness based on age or gender were detected. There were too few non-Caucasian patients to evaluate the effect of race.