Dear Dr. Fox • My male Persian cat was neutered when he was over 2 years old. He has had oxalate stones removed twice in the past two years. My cat's vet did both surgeries. What seems to be working to keep the stones away is a daily dose (0.5 cc) of liquid hydrochlorothiazide.

His dry food is Royal Canin Feline Nutrition PRO Persian 30, which is formulated to help with his urinary tract — he likes it. He drinks plenty of water but is a bit finicky about moist food. I've offered him Hill's Prescription Diet c/d, minced turkey in gravy, chicken pate and homegrown grass (he likes that), but he prefers his kibble.

The prescription is keeping the bladder stone problem in check. — A.G., Norfolk, Va.

Dear A.G. • Cats and dogs develop calcium oxalate crystals, or sand, and larger calculi, or stones, in their lower urinary tract for a variety of reasons. The acidification of manufactured pet foods — to help lower the incidence of struvite crystals — is believed to be one factor. Not drinking enough water, being given only dry food and too much sodium in the diet may also play a role in this all-too-common malady.

A moist diet and ensuring the cat drinks plenty of water (even seasoned with salt-free chicken gravy or a little milk) or getting the cat used to 5 to 10 cc of water given orally in a syringe if the cat does not drink much — these are the best preventive measures. I do not advise giving cats more salt to get them to drink more.

Dear Dr. Fox • I have a 10-year-old yellow Labrador who recently had several warts on her head and leg. The one on her face became infected and, was removed surgically. Is there anything I can do to prevent more of them from breaking out on her body? — A.K., Colts Neck, N.J.

Dear A.K. • There are two types of warts usually seen in dogs. Young dogs often develop warts caused by canine papilloma virus, which is not transmissible to humans. Older dogs are prone to developing warts because of a compromised immune system; the skin-invading virus makes the cells in the skin proliferate. Some breeds, such as toy poodles, are especially prone. Older dogs can also develop wart-like growths that are not triggered by a skin virus, but may be related to other skin conditions such as greasy seborrhea or hormonal dysfunction, especially of the thyroid gland.

If the attending veterinarian suspected possible skin cancer, a biopsy would have been taken. Smaller warts can be painted with cider vinegar three to four times a day or with over-the-counter wart removal ointment for humans. The dog, of course, should not be able to lick this medication or rub it and get it in the eyes. However, when folk remedies fail, periodic surgical removal is the only option.

www.twobitdog.com/DrFox Write to: Dr. Michael Fox in care of Universal Uclick, 1130 Walnut St., Kansas City, Mo. 64106.