Gabapentin enacarbil in Japanese patients with restless legs syndrome: a 12-week, randomized, double-blind, placebo-controlled, parallel-group study

Nov 6, 2012Current medical research and opinion

Gabapentin enacarbil treatment for restless legs syndrome in Japanese patients over 12 weeks in a controlled trial

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Abstract

The mean change in the International Restless Legs Syndrome (IRLS) score was -11.38 for patients treated with 1200 mg of gabapentin enacarbil (GEn).

Only the 1200 mg dose of GEn showed significant improvement compared to placebo (p = 0.011).
Placebo-adjusted changes in IRLS scores for GEn doses were -2.31 for 600 mg, -1.92 for 900 mg, and -2.31 for 1200 mg.
Response rates for both Investigator-rated and Patient-rated Clinical Global Impression were significantly greater for all GEn doses compared to placebo (all p ≤ 0.014).
Adverse events, including somnolence, dizziness, and nasopharyngitis, were common but mostly mild-to-moderate in severity.
There was a noted tendency for a dose-dependent increase in the incidence of adverse events.

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OBJECTIVE: Gabapentin enacarbil (GEn) was effective and well-tolerated for the treatment of restless legs syndrome (RLS) in North American studies. However, no placebo-controlled studies of GEn have been performed in Asian patients with RLS. Therefore, we investigated the efficacy and safety of GEn in Japanese patients with RLS to determine the optimal dosage.

RESEARCH DESIGN AND METHODS: Outpatients with RLS (International Restless Legs Syndrome Rating Scale (IRLS) scores ≥15) were randomized (n = 474) and treated (n = 469) in a double-blind manner with once-daily placebo (n = 116), 600 (n = 120), 900 (n = 119) or 1200 (n = 114) mg GEn for 12 weeks.

CLINICAL TRIAL REGISTRATION: NCT00530530 (ClinicalTrials.gov)

MAIN OUTCOME MEASURE: The primary outcome was the change in IRLS score. Secondary outcomes included Investigator (ICGI)- and Patient (PCGI)-rated Clinical Global Impression and adverse events.

RESULTS: The mean change in IRLS score from baseline to the final observation was -8.96 for placebo versus -11.10, -10.28 and -11.38 for 600, 900 and 1200 mg GEn. Williams' multiple comparison test showed that only 1200 mg GEn was superior to placebo (p = 0.011). However, in post hoc mixed-effects models with repeated measures, which accounted for the time-course of changes in IRLS, the placebo-adjusted changes were -2.31, -1.92 and -2.31 for 600, 900 and 1200 mg GEn. ICGI and PCGI response rates were significantly greater for all three GEn doses versus placebo (all p ≤ 0.014). Adverse events, including somnolence, dizziness and nasopharyngitis, were frequent but of mild-to-moderate severity. However, there was a tendency toward a dose-dependent increase in the incidence of adverse events.

CONCLUSIONS: GEn is effective and well-tolerated for the treatment of RLS in Japanese patients. All three doses produced improvements in IRLS compared with placebo; 600 mg GEn is a suitable target dose. However, our analysis possibly introduced positive bias by assuming that symptoms improve after discontinuation.

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Gabapentin enacarbil in Japanese patients with restless legs syndrome: a 12-week, randomized, double-blind, placebo-controlled, parallel-group study

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