Efficacy of ferric carboxymaltose (FCM) 500 mg dose for the treatment of Restless Legs Syndrome

IntroductionThere have been four randomized, placebo-controlled, double-blinded studies of intravenous (IV) iron in Restless Legs Syndrome (RLS), all of which delivered a final total dose of 1000 mg of iron. The purpose of this study was to evaluate effects of a lesser total dose (500 mg of iron).MethodsSubjects with idiopathic RLS were enrolled in a randomized, double-blinded, placebo-controlled study. Subjects received either 500 mg ferric carboxymaltose (FCM) or placebo as a single infusion (Phase I). Subjects who were previously on medication were off any RLS medications for at least two weeks prior to baseline assessment. The primary outcome variable was a change-from-baseline at week six on the International RLS Severity Scale (IRLSS) and a subject-completed Visual Analog Scale of Severity (VAS). Phase II of the study involved long-term (30 weeks) follow-up after completing the six week efficacy phase.ResultsAt week six post infusion, FCM, compared to placebo recipients, showed no significantly greater change-from-baseline for both primary outcome measures (IRLSS scale, FCM 500 mg vs. placebo: −8.3 ± 7.5 vs. −4.8 ± 8.7, p = 0.100; VAS, FCM 500 mg vs. placebo: −23.4 ± 24.1 vs. −13.3 ± 23.1, p = 0.077). None of the secondary outcome variables showed a significant difference at week six. Seven (21.9%) of the 32 subjects treated with iron in Phase I remained free from further RLS medications at 30 weeks. No serious adverse effects were found in this study.ConclusionsThis study did not show significant benefit from a single 500 mg FCM treatment for RLS symptoms. The two previous, well-controlled, trials of 1000 mg FCM showed significant treatment benefits which suggested that there may have been a clinically relevant total dose required to achieve a clinical response.