Effect of Prazosin on Recurrent Urethral Obstruction in Cats

Cassandra Gilday, DVM, North Carolina State University

Shelly Vaden, DVM, PhD, DACVIM, North Carolina State University

ArticleLast Updated July 20222 min read
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In the Literature

Conway DS, Rozanski EA, Wayne AS. Prazosin administration increases the rate of recurrent urethral obstruction in cats: 388 cases. J Am Vet Med Assoc. 2022;1-6. doi:10.2460/javma.21.10.0469

The Research …

Feline recurrent urethral obstruction (rUO) affects 11% to 58% of cats.1 Prazosin, an alpha-1–adrenoceptor antagonist, is commonly used to prevent rUO despite lack of supporting veterinary clinical studies.2,3 Prazosin has been recommended to reduce risk for recurrence because of its potential action as a urethral smooth muscle relaxant2; however, administration following urethral obstruction may cause increased patient stress from pill administration and adverse effects (eg, hypotension, lethargy, GI upset, ptyalism).

The objective of this study was to determine whether prazosin administration decreased the rate of feline rUO both prior to and within 14 days of discharge. Observational surveys were completed by clinicians who self-reported that they always or never prescribe prazosin. Development of rUO was compared in 302 (78%) cats administered and 86 (22%) cats not administered prazosin. There was no significant association between prazosin administration and risk for rUO prior to discharge; however, within 14 days following discharge, the cumulative rate of reobstruction was significantly higher in cats treated with prazosin (73 [24%]) compared with cats not treated with prazosin (11 [13%]). 

Data from this study combined with data from selected prior prospective studies showed that cats given prazosin (24%) were more likely to develop rUO than cats not given prazosin (13%).2,3 The only significant associations identified with risk for rUO were subjective difficulty performing catheterization and perception of a gritty urethra during catheterization.

The cause of prazosin’s lack of efficacy is likely multifactorial. The distal 63% to 72% of the feline urethra is composed of striated muscle, which is not relaxed by alpha-1–adrenoceptor blockade.4 Most urethral obstructions occur in the distal urethra where prazosin has no pharmacologic effect. Evidence that urethral spasms contribute to rUO in cats is lacking; treatment with urethral muscle relaxants may thus be ineffective. 

The results of this study suggest that routine use of prazosin for prevention of rUO should be discouraged.

… The Takeaways

Key pearls to put into practice:

  • Prazosin is ineffective at decreasing risk for rUO and may increase risk for recurrence.

  • Prazosin may increase patient stress, increase treatment costs, and cause adverse effects.

  • Study results suggest prazosin should not routinely be administered to prevent rUO in cats.