I am going to assume that your dog is experiencing urinary incontinence (uncontrolled leakage of urine) as that is by far the most common type of urinary problem in which long term medication is used in dogs. If I am wrong about this assumption, please let me know what your dog has been diagnosed with.
Urinary incontinence is very common in female dogs and we usually treat this with one of two drugs. First choice is usually phenylpropanolamine (PPA) which is usually given every 12 hours. The second drug we use is diethylstilbestrol (DES), which is initially give once daily, and t hen weaned to once or twice a week. The reason we usually use PPA as our first choice, is that it is less likely to have some potentially serious side effects that you can see on DES. These DES side effects are not common though and many dogs have received this drug long term without any problems.
Occasionally there is a dog where these medications are not effective, and then there are some surgical procedures that can be considered.
Oxybutynin is an anti-spasmodic type medication and is not really useful for urinary incontinence in dogs since the problem is not caused by spasming of the bladder.
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Thanks for clarifying.
If she is squatting to urinate, then it would not be considered incontinence. If you are finding wet spots where she is laying or she drips urine and is unaware of it, then that would be considered incontinence. It doesn't sound that this is incontinence.
To answer your original question, oxybutynin can be used long term, but it rarely is necessary. Usually when symptoms persist as you are describing it is because the original problem hasn't yet been resolved. It is possible that your dog may need a longer course of antibiotics or possibly even a different antibiotic if the infection present is resistant to the first antibiotic they used. Also, if it has not already been done, it would be a good idea to have x-rays taken to check for urinary bladder stones as this is often the cause of recurrent UTI symtpoms.
Let me know if you have additional questions.
There are but I don't think they offer any advantages over the oxybutinyn as they also have to be administered every 8 - 12 hours and since the oxybutinyn does work, it would be just as well to stick with that one.
Oxybutynin does come in a extended release form, but I could not find a dose for dogs for this. There is a good chance that no one has done any studies to figure this out. Before using it, I would suggest that your vet consult with a veterinary pharmacologist who could maybe make some calculations to try to figure out what a presumed safe dose for dogs would be.
Other urinary tract antispasmodics include prazosin, propantheline, pheoxybenzamine, dantrolene, imipramine, and diazepam.