Dear Doctor: Why is a much lower dose of medicine now doing the trick?


Q. Our dog, now almost 7, has been on daily Proin since she came to live with us as a puppy. She had been dribbling urine without actively trying to, and we were told she needed to be on the medicine for life since the sphincter in her bladder was weak/slack, perhaps as a result of being spayed, and the drug would keep it more taut. Originally, we tried slowly increasing doses in order to keep her on as little of the medicine as possible, since in some cases it can raise blood pressure: a half pill each day, one pill a day, one and a half pills a day, and two pills a day (25 milligrams each). Nothing worked except two pills a day. Anything less, and she dribbled urine. Every once in a while for the first couple of years we’d try reducing the dose. It would seem to work for a day or two, and then she’d be back to dribbling.

Well, several weeks ago, we forgot to go to the doctor to refill her prescription on a Saturday, which meant she had no Proin till Monday. She did fine. We thought a couple of days wasn’t all that telling, but we decided to try going to one pill a day (half in the morning and half at night) rather than two to see what happened. It has been a while now, and there has been no problem whatsoever. We are thinking of keeping her on one pill a day for three months and then going down to a half pill a day to see what happens.

How could this be? Why, now, would half the dose she has been taking for years be working — when it did not work when she was younger? I don’t think it could be a matter of her being more mature and better able to hold in her urine because it wasn’t about that. This was something over which she had no physiological control. Thanks for any information you can provide.

Harry Winter

Marblehead, Massachusetts

Dear Mr. Winter,

A. Proin is the brand name for phenylpropanolamine, or PPA, and it is possible that a dog will become more responsive to its effects after being off the drug for a bit. Consider that PPA binds to the receptors that cause the smooth muscle of the urethra leading away from the bladder to be able to contract. That contracting is what allows a dog to hold in her urine. But with high doses or long-term use, the receptors will become resistant to the drug.

Sometimes, though, after being off PPA for a time, the receptors in the dog’s bladder will actually regenerate. That’s what will allow a dog to respond to the drug at a lower dose.

Also, says Mary Labado, DVM, a small animal urology specialist at the Tufts Cummings School, “the dog as a youngster might have had an infection, which would have resulted in less of a response, and now infection is not an issue.” It’s also possible, Dr. Labado says, that maybe over time the dog did in fact develop more of an ability to control her urination. The urine dribbling when she was a pup might have also been triggered by a submissive, anxious nature that over time has morphed into a personality that’s more mature and confident.

Whatever the reason for your dog’s ability to respond to a lower dose of Proin, it’s a good thing. The drug is generally very safe, but as with any medications, there are risks for side effects. One is increased blood pressure, which is why all dogs on Proin should periodically have their blood pressure checked to make sure it hasn’t skyrocketed into an unhealthy range. Other side effects, also not very likely but still possible, include restlessness, hyperactivity, increased heart rate, irritability (the drug is a stimulant), aggressive behavior, and even allergic reactions or seizures. (Proin was once on the human market as the diet drug Dexatrim but was removed because of various health risks.)


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