Hormone Replacement Therapy in Dogs

Hormone replacement therapy is a medical treatment used in dogs to treat urethral sphincter mechanism incompetence (USMI). USMI is the most common non-neurogenic cause of urinary incontinence in female dogs and is referred to colloquially as spay incontinence. The goal of hormone replacement therapy is to return tone to the urethra to decrease the incontinence. Hormone replacement therapy will be prescribed by your veterinarian and given at home. 

Diagnosis of USMI is typically based on signalment (breed, age, sex), history, and lack of other causes of incontinence found during physical examination. Most commonly USMI is seen in spayed dogs of medium to large size. Certain breeds are predisposed to this condition including Boxers, Doberman Pinschers, English Springer Spaniels, German Shepherds, Irish Setters, Old English Sheepdogs, Rottweilers, and Weimaraners. Other factors that predispose to this condition include docked tail and obesity. 

The gold standard diagnostic test is a urethral pressure profile. For this test a urinary catheter is placed in an awake or lightly sedated dog and removed at a constant rate while warm sterile water is infused. The pressure generated in the urethra is then measured.  This is a 15-30 minute procedure that requires no anesthesia.

Once a diagnosis is made, your veterinarian will prescribe your dog the necessary medicines to treat USMI: Estrogen (DES) and/or Phenylpropanolamine (PPA), an alpha-1 adrenergic agonist. DES is prescribed as a daily pill and then slowly tapered to a low dose maintenance schedule. PPA may be used in addition to DES and will also be tapered to a maintenance schedule from a three time per day dose. 

Hormone replacement therapy is generally regarded as successful. The effects of the therapy last as long as the drug remains in your dog’s system to help with their urethral tone. An alternate treatment to hormone replacement therapy is collagen injection into the submucosa of the urethra to physically decrease the size of the urethra and improve incontinence. This procedure is done under general anesthesia. Collagen injections may need to be repeated after a year as the collagen degrades and retreatment is often successful as well. 

Hormone replacement therapy in dogs is an onging treatment that requires regular administration of prescribed medications.

Hormone replacement therapy in dogs is a lifelong commitment as these drugs serve to replace estrogen that would have otherwise been produced in an intact female. Sometimes dogs begin to show signs of incontinence even while on this therapy. In that case, the dose will have to be increased. If the dose needs to be repeatedly increased, your dog could become at risk for adverse effects of DES therapy including bone marrow suppression, estrus-like symptoms, and alopecia. The benefit of DES is that it is cost-effective and can become a manageable routine for you and your dog in time. 

Hormone replacement therapy in dogs is a lifelong commitment as these drugs serve to replace estrogen that would have otherwise been produced in an intact female. Sometimes dogs begin to show signs of incontinence even while on this therapy. In that case, the dose will have to be increased. If the dose needs to be repeatedly increased, your dog could become at risk for adverse effects of DES therapy including bone marrow suppression, estrus-like symptoms, and alopecia. The benefit of DES is that it is cost-effective and can become a manageable routine for you and your dog in time. 

Preventing USMI seems like it should be as simple as not spaying your pet. However, not spaying your dog could lead to different health problems for them down the road, most notably mammary tumors and behavioral problems, and is not recommended. Knowing which dogs are prone to developing USMI will help you prepare for the possibility of needing hormone replacement therapy in the future. In addition, keeping your dog at a healthy weight could help prevent USMI and the need for therapy. Taking your dog on regular walks or trips to the dog park and carefully monitoring their food and snack intake will help keep your dog at a healthy weight.