SUMMARYRetigabine (RTG; international nonproprietary name)/ ezogabine (EZG; North American adopted name), a firstin-class antiepileptic drug (AED) that reduces neuronal excitability primarily by enhancing the activity of KCNQ2/ 3 (K v 7.2/7.3) potassium channels, has recently been approved by the European Medicines Agency and the U.S. Food and Drug Administration as adjunctive therapy in adults with partial-onset seizures. Much of the RTG/EZG safety profile will be familiar to health care professionals who are experienced with the clinical use of AEDs. RTG/EZG, as a potassium channel opener, also has a pharmacologic effect on smooth muscle of the urinary bladder. Consequently, the adverse event (AE) profile of RTG/ EZG includes a potential risk of effects on the urinary system. This review summarizes the urinary safety profile and any secondary renal effects of RTG/EZG using data from patients in the pivotal controlled trials and the overall phase 2/3 clinical development program. Urinary AEs were reported more frequently in patients receiving RTG/EZG compared with placebo, although most patients were able to continue with treatment. Specifically, there is an increased risk of urinary retention with RTG/EZG, with urinary hesitation representing the most frequently reported urinary retention-related AE. Potential secondary renal effects, which may be caused by an inability to empty the bladder, were evaluated. Crystals with a bilirubin-like appearance were detected in the urine of patients receiving RTG/EZG. Although investigations indicated that these crystals were not bilirubin, their composition remains undetermined. There was no causal association with urinary tract infections, and nephrolithiasis was uncommon. The reported clinical effects of RTG/ EZG are consistent with its documented effects on bladder smooth muscle in preclinical studies. RTG/EZG should be used with caution in patients at risk of urinary retention.

We assessed the efficacy and tolerability of gabapentin enacarbil in the treatment of moderate to severe primary restless legs syndrome and associated sleep disturbance. This was a multicenter, randomized, double-blind, placebo-controlled, 2-period crossover polysomnography study of gabapentin enacarbil 1200 mg or placebo taken once daily. Subjects were randomized 1:1 to a sequence of gabapentin enacarbil:placebo or placebo:gabapentin enacarbil, receiving each treatment for 4 weeks. The primary end point was the mean change from baseline at weeks 4 and 10 (4/10) last observation carried forward in wake time during sleep. The key secondary end point was the mean change from baseline at weeks 4/10 last observation carried forward in periodic limb movements associated with arousal per hour of sleep. Tolerability assessments included adverse events. One hundred thirty-six subjects were randomized (gabapentin enacarbil:placebo, 67; placebo:gabapentin enacarbil, 69), and 114 (gabapentin enacarbil:placebo, 53; placebo:gabapentin enacarbil, 61) completed the study. Gabapentin enacarbil 1200 mg significantly reduced wake time during sleep (mean change from baseline [adjusted mean treatment difference]: -26.0 minutes; P < .0001) and periodic limb movements associated with arousal per hour of sleep (adjusted mean treatment difference: -3.1 periodic limb movements with arousal/hour; P = .002) compared with placebo at weeks 4/10 last observation carried forward. The most commonly reported adverse events were dizziness (gabapentin enacarbil 20%, placebo 2%) and somnolence (gabapentin enacarbil 13%, placebo 2%). Gabapentin enacarbil 1200 mg once daily significantly reduces restless legs syndrome-associated sleep disturbance and periodic limb movements associated with arousal per hour of sleep and is generally well tolerated in adults with moderate to severe primary restless legs syndrome.

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