Urinary incontinence is most commonly caused by urethral sphincter incompetence. It is most common in large breed, spayed female dogs (11–20% incidence) but may be seen in intact females, male dogs, and cats. Estradiol-17β concentrations decrease after ovariohysterectomy in bitches, resulting in deterioration of urethral closure within 3–6 mo. Currently, there are no approved drugs for the treatment of incontinence in animals, and most of the human products traditionally used have been removed from the market due to toxicity concerns. Some estrogen compounds and α-adrenergic drugs may still be available to veterinarians through compounding pharmacies (see Systemic Pharmacotherapeutics of the Urinary System: Drugs Used to Treat Urinary Incontinence).

Table 3
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Drugs Used to Treat Urinary Incontinence Drug Dosage Diethylstilbestrol Dogs: 0.1–0.3 mg/kg/day, PO, for 7–10 days, followed by 1 mg/dog/wk Phenylpropanolamine Dogs: 1.5–2 mg/kg, PO, sid-tid Ephedrine Dogs: 1.2 mg/kg, PO, bid-tid Cats: 2–4 mg/kg, PO, bid-tid Pseudoephedrine Dogs >25 kg: 30 mg/dog, PO, tid Dogs <25 kg: 15 mg/dog, PO, tid Testosterone propionate Dogs: 2.2 mg/kg, IM, every 2–3 days Testosterone cypionate Dogs: 2.2 mg/kg, IM, every 30–60 days

Diethylstilbestrol (DES) is a nonsteroidal estrogen derivative that closely resembles the natural estrogen, estradiol. Because it is inexpensive and infrequently administered, it is the first choice for treating urinary incontinence in female dogs. It is orally bioavailable and reaches peak plasma concentrations in 1 hr in dogs; it has an elimination half-life of 24 hr due to enterohepatic recirculation. Estrogens sensitize the urethral sphincter to α-adrenergic stimulation; therefore DES therapy is synergistic with α-adrenergic drugs. DES is given as a daily loading dose for 7–10 days and then reduced to once weekly dosing, if possible, to avoid toxicity. Treated dogs are extremely susceptible to bone marrow suppression from estrogen, typified by early thrombocytopenia and potentially fatal aplastic anemia. Hematopoietic toxicity is rarely seen in cats. Other adverse effects seen in dogs include alopecia, cystic ovaries, cystic endometrial hyperplasia, pyometra, prolonged estrus, and infertility. When used once weekly in spayed female dogs, adverse effects from DES are rare.

α-Adrenergic agonists such as phenylpropanolamine (PPA), ephedrine, pseudoephedrine, and phenylephrine act directly on smooth muscle receptors to increase urethral tone and maximal urethral closure pressure. Although often more clinically effective than DES, their action is short lived, usually requiring dosing bid-tid. Of this class of drugs, PPA is the most effective and produces fewer cardiovascular side effects. Previously available in over-the-counter cold medications and appetite suppressants, it was withdrawn from the human market because of toxicity associated with overuse as a diet aid. It may still be available from some compounding pharmacies. Ephedrine, pseudoephedrine, or phenylephrine may be tried if PPA is unavailable. Adverse effects of α-adrenergic drugs include excitability, restlessness, hypertension, and anorexia.

In male dogs, testosterone injections are used to treat urinary incontinence but are generally less effective than estrogen therapy in female dogs.

Last full review/revision March 2012 by Patricia M. Dowling, DVM,MSc, DACVIM, DACVCP