Page 3 - Diagnosing and managing urinary incontinence in dogs

Urinary incontinence can occur before spaying in some breeds such as Greater Swiss Mountain
dogs, Soft Coated Wheaten terriers, Dobermans and Giant Schnauzers. The main mechanism for
the development of urinary incontinence with PSMI has traditionally been attributed to low urethral
closure pressure, though some dogs have a bladder component to this form of urinary incontinence
(Nickel RF Vet Rec 1999). Urethral closure pressure is decreased 12 to 18 months following spaying
in normal dogs (Arnold S. Schweizer Archiv fur Tierheilkunde 1997; Salomon JF; Vet Record 2006)
and it is speculated that this pressure continues to decline with age.

Phenylpropanolamine (PPA) is the initial treatment of choice to restore urinary continence in dogs
with PSMI. Incontinence is controlled in 75-90% of female dogs with PSMI treated with the α-
adrenergic agonist PPA at a dosage of 1.0-1.5 mg/kg PO q12h or q8h (standard preparation). PPA
is also available as a sustained release product (Cystolamine®; 75 mg capsule). More than half of
the dogs that failed to respond with the standard formulation of PPA became continent when treated
with a sustained release formulation of this drug (Bacon NJ 2002). Once daily administration may be
desirable for many owners. The recommended dosage of Cystolamine® is ½ capsule PO q24h for
dogs < 18 kg, 1 capsule PO q24h for dogs 19-45 kg, and 1 ½ capsules PO q24h for dogs > 45 kg.

MUCP is increased on the UPP after treatment with PPA.

Virtually all affected dogs have some improvement in continence after treatment with PPA. The
largest dose should be given at night to control incontinence while the dog is sleeping. In dogs with
incontinence only at night, dosing only at night can be effective. PPA may become less effective with
prolonged use (so-called tachyphylaxis). Occasionally, simply increasing the dosage of PPA is

sufficient to regain control of continence. Potential adverse effects include restlessness and
hypertension.

Relative contraindications to use include known underlying cardiac disease, chronic kidney disease,
or systemic hypertension. Although systemic hypertension did not develop after months of PPA
exposure to young dogs in an experimental setting, we have observed client-owned dogs with PSMI

on PPA that have developed systemic hypertension. We recommend systemic blood pressure be
measured before beginning PPA treatment and periodically thereafter to identify the development of
systemic hypertension.

Estrogens are an effective treatment for PSMI in many dogs and can be given much less frequently
than PPA. Incontinence is controlled in 60-65% of affected dogs treated with estrogens alone for

PSMI. Estrogen increases the sensitivity of urethral α-adrenergic receptors to catecholamines; they
also may increase the number of receptors. The MUCP is increased on the UPP after treatment
with estrogens.