Does Repeated Dosing of Intravenous Ferric Carboxymaltose Alleviate Symptoms of Restless Legs Syndrome?

Background: Several studies have reported the efficacy of intravenous (IV) iron for patients with restless legs syndrome (RLS), but little is known about the efficacy or safety of repeated IV iron treatment. The aim of this study was to evaluate the effectiveness of repeated doses of IV ferric carboxymaltose (FCM) in treating RLS symptoms. Methods: Patients who received FCM more than twice for RLS from April 2016 to January 2020 were retrospectively reviewed. Patients who had shown positive response to initial IV FCM re-visited the clinic when their symptoms returned, and received repeated IV FCM (1000 mg). Blood iron panels were measured before initial and repeated IV FCM. We defined 'responders' as patients with a greater than 40% decrease in International Restless Legs Study Group Severity Scale (IRLS) compared with pre-treatment levels. Results: A total of 42 patients, including 26 with primary RLS, 5 with gastrectomy, and 11 with anemia, completed the evaluation. Patients received IV FCM infusion 2-4 times. A total of 21 of 26 (80.8%) primary cases of RLS, 4 of 5 (80.0%) patients with a history of gastrectomy, and 9 of 11 (81.8%) patients with anemia responded to repeated FCM treatment. Serum ferritin levels of patients with primary RLS were higher before the second treatment than the baseline levels. There were no serious adverse events observed in the study. Conclusions: Repeated IV FCM for recurring symptoms is an effective treatment for primary RLS and RLS associated with iron deficiency. Serum ferritin might not be a reliable factor to monitor the sustained effects of IV iron for RLS.