The urinary safety profile and secondary renal effects of retigabine (ezogabine): A first-in-class antiepileptic drug that targets KCNQ (Kv7) potassium channels

Retigabine (RTG; international nonproprietary name)/ezogabine (EZG; North American adopted name), a first-in-class antiepileptic drug (AED) that reduces neuronal excitability primarily by enhancing the activity of KCNQ2/3 (Kv7.2/7.3) 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.