Which adrenergic agent is used to treat urinary incontinence in dogs?

• A. Succinylcholine
• B. Tiletamine
• C. Propranolol
• D. Phenylpropanolamine

Answer: (D)

Increasing urethral sphincter tone is the key strategy for treating urinary incontinence due to urethral sphincter mechanism incompetence in dogs. An alpha-adrenergic agent stimulates the smooth muscle of the internal urethral sphincter, raising its closure pressure and reducing leakage. Phenylpropanolamine is a peripheral alpha-1 adrenergic agonist given orally, and it directly enhances sphincter tone to improve continence in many dogs, especially in spayed females. That’s why it’s the best choice here.

The other drugs don’t achieve this effect. Succinylcholine is a depolarizing neuromuscular blocker that would weaken muscles rather than support continence. Tiletamine is an anesthetic agent, not a therapy for urinary incontinence. Propranolol is a beta-blocker and does not increase urethral sphincter tone; it could even interfere with sympathetic effects that help continence.