The effect of prazosin on outcome in feline urethral obstruction.

Objective: To determine whether prazosin administration following urethral obstruction (UO) reduces the risk for recurrent urethral obstruction (rUO) or lower urinary tract signs, and to document adverse effects associated with prazosin use in cats.

Design: Double-blinded, prospective, interventional study.

Setting: University teaching hospital.

Animals: A population of 47 consecutive male cats with UO not associated with urinary tract calculi >2 mm in diameter.

Interventions: Cats were randomized to receive either prazosin (0.25 mg/cat PO q 12 h, n = 27) or placebo (n = 20) for 1 month following UO.

Measurements And Main Results: Cats were monitored for rUO, severity of lower urinary tract signs, and medication adverse effects during hospitalization and through weekly conversations with the owner during the 1- month study period and once more at 6 months following discharge. There was no difference in the rUO rate among cats that received prazosin or placebo prior to hospital discharge (2/26 (7%) versus 1/19 (5%), P = 1.00), during the 1- month medication period (4/26 (15%) versus 3/18 (17%), P = 0.776), or at 6 months following treatment for UO (7/19 (37%) versus 4/13 (31%), P = 0.811). There was no difference in the severity of lower urinary tract signs reported by the owners at the 1-, 2-, 3-, or 4-week follow-up periods among the cats in either group (P = 0.62, 0.68, 0.33, 1.00, respectively). Reported adverse effects from prazosin administration included lethargy, ptyalism, diarrhea, anorexia, and malodorous stool.

Conclusions: Although our study results failed to find a difference in the incidence of rUO and severity of lower urinary tract signs among cats receiving prazosin and those receiving placebo, these study results should be interpreted cautiously as our study was underpowered to identify such differences. Larger placebo-controlled, prospective studies are needed to determine the clinical utility of prazosin in prevention of rUO.