Influence of phenylpropanolamine and ephedrine on the urethral closure pressure and the arterial blood pressure of spayed bitches

Urinary incontinence in the bitch is the most disagreeable side effect of s paying. This may be successfully treated in most cases by the use of sympat homimetic agents. Ephedrine-hydrochloride or phenylpropanolamine are most c ommonly used. In humans their use may lead to an increase of the arterial b lood pressure. In the dog no comparative studies have been done on the effe ct of these two substances on the urethral closure or on the possible side effects to the circulatory parameters. A randomised double-blind study was performed in 10 spayed bitches, before and after treatment with phenylpropa nolamine and ephedrine-hydrochloride at the recommended doses (1.5 mg/kg BW per os bid), to objectively record the urethral closure and to examine the substances for their side effects on the circulatory parameters and the pu lse frequency. Both substances, phenylpropanolamine and ephedrine-hydrochloride significan tly increased the urethral closure pressure from 5.85 cm H2O (untreated bit ches) to 8.9 cm H2O (52 %) and to 10.3 cm H2O (76 %), respectively. However , the response was for each different. Unexpectedly both substances signifi cantly reduced the arterial blood pressure by 5 to 6 mm Hg and the pulse fr equency by 20 to 25 beats per minute. It may be assumed that, this unexplai ned phenomenon has no clinical consequence. Phenylpropanolamine and ephedrine-hydrochloride have an equally potent effe ct on the urethral closure. No side effects have been observed and both sub stances can therefore be readily given to incontinent bitches.