Urinary incontinence in female dogs is quite common. The anatomy of the lower urinary tract consists of the bladder and the urethra which in female dogs empties into the vagina. There is a muscular sphincter at the top and bottom of the urethra. When these muscles are constricted, or tightened up, they prevent urinary flow from the bladder. Those muscles relax and open when the dog is voiding. Certain hormones in the body, most notably estrogen, have an effect on these muscles and keep them tight. When a female dog is spayed, the primary source of estrogen, the ovaries, are usually removed. With less estrogen in the body, the urinary sphincters can start to get a little loose, and then the dog will leak urine. Typically this happens when she is lying down, however sometimes dogs will dribble urine when they are walking or standing as well. The classic sign of urinary incontinence is that there will be a wet spot in the area that the dog was just laying. If your dog is exhibiting these symptoms, you should consult with a veterinarian. The first thing that your veterinarian will want to do is screen for a urinary tract infection. Urinary tract infections will sometimes cause urinary incontinence because the infection causes inflammation around the sphincters. If there is no infection, then there are several medications that can be used to manage urinary incontinence.
Each of these medications have the aim of tightening the urethral sphincter. One medication is called phenylpropanolamine (PPA). Proin is a common trade name. PPA increases smooth muscle tone of the urethra and urethral sphincters and is typically administered 2-3 times a day. This medication is close in chemical structure to ephedrine, which used to be found commonly in human weight loss supplements. Ephedrine was banned for use in weight loss products for a period of time because of its potential abuse as a stimulant. This drug became available again in weight loss products, but with more stringent regulation. PPA can increase blood pressure, so it should be used cautiously in dogs with cardiovascular problems. That being said, dogs tend to tolerate PPA quite well with minimal side effects.
Another class of medications commonly used to treat urinary incontinence are estrogen supplements. Estrogens work in similar way to PPA, but usually are only administered every 5-7 days. Hormone supplements for urinary incontinence have been associated with bone marrow suppression and severe anemia. That being said, this side effect is exceedingly rare. Most likely because we now know that we can use tiny amounts of this supplement to get the beneficial effects on the urethra.
Male dogs can also get urinary incontinence, but it is not as common as it is in female dogs. Most cases of urinary incontinence respond well to either PPA or estrogen supplements (which are not usually used in males). There are some female patients who will require BOTH estrogen and PPA, but that is not very common.