Dear Dr. Thompson: Our 3 1/2-year-old miniature schnauzer had surgery in January for bladder stones. After the surgery she was put on prescription canned SD food and antibiotics for six weeks. She then went to a dry prescription CD food. A recent urinalysis showed a pH of 8 and some tiny crystals. She is going back on the canned SD and antibiotics for 10 days. Our veterinarian wanted another culture and sensitivity but we can't afford to keep having them done. Do you know of any other treatment to prevent the stones?
I'm sorry to hear that your dog has experienced so much trouble with bladder stones at such a young age. A little background on what constitutes stones and how they form helps to understand prevention and treatment.
Dogs commonly develop two major types of stones that reflect their chemical composition: calcium oxalate and struvite. There are unusual forms like urate stones, but those are linked to liver disease and not likely an issue for your pet.
Calcium oxalate stones are increasingly more common and more difficult to prevent. Supplements, excess vitamin C, and the acidity of the urine falling outside a narrow range can cause crystals to precipitate in the urine and these can aggregate into stones.
Preventive strategies are mainly centered around increasing water consumption and avoiding the main triggers for development.
What you have described leads to me to believe that your dog has struvite stones. Those are most commonly caused by infection with a type of bacterium called urease positive. The infection raises the pH of the urine and this allows the struvite crystals to form. The diets you were prescribed are intended to make her urine more acidic and hopefully prevent the crystals from forming. However, if a persistent infection is still an issue, the diet will be less effective.
Your veterinarian wanted to run another test to determine whether she has developed a resistant infection. Antibiotic-resistant bacteria can develop after long-term therapy, and a culture and sensitivity will make sure you are using the right drug to clear the infection completely. Some dogs who get re-infected may need prophylactic antibiotic therapy as prevention.
Normally, the dietary management is very effective in making the urine more acidic, but any outside food sources can sufficiently alter the urine composition, so hopefully she has been on the prescription food only. Unfortunately, in the short-term you may need some trial and error to eliminate whether the source of infection has completely cleared. This may mean another culture to make sure the urine is free of bacteria, but over the long term it is less expensive than another surgery to remove the stones and will help keep her from dealing with a painful condition. It sounds like you are in goods hands, so good luck.
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