Ah, I see.
Now we can see spay associated incontinence in female dogs, but this isn't due to anything amiss with the operation. The nature of the incontinence is that removal of the uterus can lead to a drop in estrogen produced in the body. This lack of hormone can lead to a weakening of the urinary sphincter's musculature and this is why we see dribbling (especially in sleep when she cannot exercise 'conscious control'). It is the same phenomena we see in older human females when they are undergoing menopause. And in that vein, we would expect to see this as a problem of the older spayed female dog.
Now if she were a dog with an estrogen deficiency (despite being quite a bit younger then we would expect for such signs) then I would expect you to tell me that this medication has worked for her (since it would be tightening that bladder sphincter)
It is because she is so young and the medication doesn't sound to be helping, that I would consider a further diagnostic work-up to make sure there isn't an abnormality of her urinary tract that has been causing this dribbling. There are a range of conditions that can be to blame (& can be present from day one or develop as she grew). These issues can range from abnormal position of the neck of the bladder relative to the vagina, to strictures, to mispositioned (ectopic) ureters that deposit urine past the portion of the bladder that is supposed to be keeping it at bay. And how we can manage it can vary depending which issue is actually causing her trouble.
So, I would consider discussing the situation with your vet or even consider referral to a specialty practice. With a physical exam and a full history, the specialist will be able to decide which diagnostic tool is most likely to reap the information we are looking to find. That said, I do want to give you a wee idea of some of the diagnostic options that might be appropriate in her case (which to do will depend on what the vet can appreciate on physical exam).
While plain x-rays can tells us if the kidneys or bladder are abnormal, we need contrast x rays. This is where a special radio-opaque contrast is given intravenously and then xray is used to watch how it moves through the kidneys and then tracks down the ureters into the bladder. It allows us to visualize the flow of the urine and can tell us if the ureters are in the right place. And of course, like normal x rays will help determine if bladder/kidney anatomy and positioning is normal.
As well, retrograde contrast studies are sometimes used to look at the urinary system from the vagina up. This is done by using a different type of contrast put into the bladder via the urinary tract and then again watching with xray for abnormalities.
Alternatively, specialist ultrasonographers (I am afraid GP's aren't often savvy enough) can visualize the ureters with their ultrasound and watch the little jets of urine as they are shot into the bladder. This, again, can allow visualization of what is going on with the ureters and can also give us an in-depth look at what is going on in the kidneys.
Vagino-urethrography is another consideration when working up dogs in this situation. This is where a scope (with a little camera) is passed from the vagina and into the bladder. This allows the vet to see if there are any abnormalities of the vagina, and the bladder (as well they can sometimes spy those jets of urine this way as well).
So, I would advise because she is a young dog who isn't really responding to this medication, it is worth a closer look into her situation. I would advise having her seen, preferably by a urinary/internal medicine specialist. They will be able to assess her situation and hopefully get to the bottom of what is causing her dribbling. Depending on what issue is identified, they will be able to guide you on the best way of addressing it. And most of all, once you know what you are actually dealing with, you will be in a much better position to manage it appropriately and enjoy spending time with your dog.
I hope this information is helpful.
Please let me know if you have any further questions.
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