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Dear Most Esteemed and Knowledgeable Kitties:

A couple of months ago, my 9-year-old male cat became quite ill. His symptoms were primarily lethargy and decreased appetite. We took him to the vet where his blood work revealed an elevated neutrophil count, but his white blood cell count was otherwise normal. The vet prescribed antibiotic prophylactically. Now my cat’s immediate symptoms are resolved, but he is left with what seem to be neurological problems including balance disturbance and pupils oddly dilated. I’m concerned that he may have mercury poisoning as I have given him tuna on a regular basis. Are there diagnostics and treatment for that? Do you have any other ideas of what may be going on with him?


Siouxsie: Our research indicates that while an occasional tuna treat is okay, there are a number of hazards to regularly feeding tuna to your cat.

Thomas: Too much tuna can lead to vitamin E deficiency, resulting in yellow fat disease, or steatitis. Symptoms include loss of appetite, fever and hypersensitivity to touch due to inflammation and necrosis of fat under the skin.

Dahlia: Cats that eat too much tuna can develop other nutrient deficiencies, because most de-boned fish doesn’t have enough calcium, sodium, iron, copper, and is also lacking in several other vitamins.

Siouxsie: The high levels of mercury in tuna can be dangerous, too. If tuna is fed occasionally, it’s not a big deal — but if you feed him tuna every day, you could be risking mercury poisoning.

Thomas: So what are the symptoms of mercury poisoning? According to the Merck Veterinary Manual, signs of mercury poisoning in cats may include over-excitement, irritability, incoordination, convulsions, stiff hind legs, tremors and blindness.

Dahlia: Mercury poisoning is pretty rare in cats, and in people. It is usually diagnosed by a blood test or a test of the hair/fur.

Siouxsie: If a diagnostic test indicates that your cat has mercury poisoning, a therapy called chelation can be done to eliminate the mercury from his body.

Thomas: So, if your cat is suffering from mercury toxicity, it can be treated. But now we’re going to tell you about one of our favorite axioms, the Horses, Not Zebras Theory. Basically, Horses, Not Zebras says that if you hear hoofbeats outside your window (and you don’t live on the African savanna), it’s much more likely to be a herd of horses than a herd of zebras.

Dahlia: In short, the cause of your cat’s symptoms is likely to be something much more common (horses) than mercury poisoning (zebras).

Siouxsie: If your cat didn’t start showing neurological symptoms until after he began his course of antibiotics, the symptoms may be a side effect of the medicine.

Thomas: This is still a bit on the zebra-ish side, because very few antibiotics have neurological side effects, and even for those that do have known neurological side effects, the incidence of these effects is incredibly rare.

Dahlia: The fluoroquinolones are powerful antibiotics that are commonly prescribed for pets. The most widely used fluoroquinolones are enrofloxacin (Baytril®), ciprofloxacin (also known as cipro), orbifloxacin (Orbax®) and marbofloxacin (Zeniquin®).

Siouxsie: They are used to treat infections of the skin, bladder, ears, kidneys, lungs (pneumonia), and prostate gland. A liquid solution is also made in the form of ear drops to treat ear infections.

Thomas: In very rare cases, cats receiving high doses of Baytril® have developed severe, irreversible vision problems. Researchers believe this adverse reaction is unlikely at lower doses, though.

Dahlia: Mama says Thomas had to take Baytril® before, when he was a wee, sick shelter kitty, and he’s just fine! Sinéad had to take it a few times for UTIs, and she never had any neurological problems as a result.

Siouxsie: For more information about fluoroquinolone antibiotics and side effects, check out this page on noted veterinarian Dr. Eric Barchas’s website.

Thomas: This page at vetinfo.com has a list of side effects of common veterinary antibiotics used on cats.

Dahlia: Jane, you really need to get in touch with your vet and let them know that your cat is having these symptoms. Whether it’s mercury, an antibiotic reaction, or something else entirely — only your vet will be able to solve the mystery.

Siouxsie: Please keep in mind that this information is not in any way intended to be a diagnosis. Even if we were licensed vets, we’d never make a diagnosis without seeing your cat and performing diagnostic tests!

Thomas: However, we hope we’ve helped you to know what questions to ask your vet when you take your cat back to the clinic.

Dahlia: Good luck, Jane. Please let us know how things turn out.