Urethral plugs are a common cause of feline urethral obstruction, frequently occurring in the postprostatic penile urethra (ie, the narrowest portion). Many smooth and skeletal muscle relaxants have been evaluated to relax the urethral musculature, reducing potential for secondary urethral damage; only those acting on striated muscle are useful for relaxing the musculature of the postprostatic penile urethra. Dantrolene and succinylcholine have been effective in this application but have potential systemic side effects. Atracurium besylate (AB) is a neuromuscular-blocking agent that does not depend on liver or renal function for metabolism.

In this nonblinded study of 2 groups of cats with urethral plug obstruction, saline (4 mL, n = 20) or AB solution (0.5 mg/mL, n = 25) was instilled in the urethra followed by retrograde flushing; this was repeated until plug removal was achieved. The percentage of cats in which plug removal was achieved at first attempt was higher in the AB group than in the control (64% vs 15%, respectively). The mean time required for removal was shorter in the AB group than for the control (21.1 ± 16.2 seconds vs 235.2 ± 132.4 seconds, respectively). Intraurethral administration of AB appeared to be a safe, effective way to decrease the time needed to relieve urinary obstructions.

Commentary
Reestablishing urethral patency in male cats with urethral plugs typically involves retrograde flushing via urethral catheterization. Urethral irritation or inflammation leading to contracture of the urethral musculature can impede retrograde flushing. IV smooth and striated muscle relaxants may facilitate retrograde urethral flushing but may also have adverse systemic effects. This study provided the first evidence that intraurethral administration of a skeletal muscle relaxant (eg, AB) is effective without apparent systemic side effects. Since urethral and bladder pressures were not measured, efficacy of the intraurethral infusion could be associated with decreased intravesicular pressure as well as decreased intraurethral pressure.—Gregory F. Grauer, DVM, MS, DACVIM

Source
Effect of intraurethral administration of atracurium besylate in male cats with urethral plugs. Galluzzi F, De Rensis F, Menozzi A, Spattini G. J SMALL ANIM PRACT 53:411-415, 2012.