If Fluffy isn't eating as well as he should, your vet might recommend vitamin B12 shots to kickstart his appetite. That's especially true if the reason for his appetite loss is an underlying disease or medical treatment for that condition. He needs calories to help him pull through.
Cobalamin, the scientific name for vitamin B12, is necessary for your cat's metabolism. Under normal circumstances your cat can store this vitamin in his body. If he's sick or his immune system becomes compromised, that may no longer be the case. Your vet will test Fluffy's serum cobalamin levels, recommending supplementation if these levels fall to near or below normal. Supplementing with injectable vitamin B12 is very safe, since it's a water-soluble vitamin. That means any excess goes through Fluffy's kidneys and out in his urine.
According to Texas A&M; University's Department of Veterinary Medicine and Biological Sciences, cobalamin might have a "pharmacologic effect as an appetite stimulant." It notes that feline patients who don't eat and have a vitamin B12 deficiency often start eating again after receiving injectable cobalamin supplements. Once the injections stop, the cats also stop eating. That's true even if the cat has a a normal serum cobalamin level when tested. If that's the case, vitamin B12 shots should be given every week or two.
Cats undergoing chemotherapy for cancer often lose their appetites. That's also true of cats suffering from exocrine pancreatic insufficiency, which results in a vitamin B12 deficiency. Cats with EPI will require regular cobalamin injections for the rest of their lives, along with special pancreatic enzymes mixed into their food. If your cat's diagnosed with liver disease, he probably doesn't have enough cobalamin in his system. In addition to loss of appetite, his gastrointestinal system is unlikely to digest vitamins well. Weekly vitamin B12 injections can perk up his appetite and help his intestinal system function better.
In addition to the injectable form of vitamin B-12, an oral paste and transdermal version are also available. These might be alternatives for your cat if getting him to the vet every week isn't possible for you. The injectable version goes into his system more directly, so your vet will adjust the oral or transdermal dosages with that in mind. Fluffy might not mind the oral paste, as it tastes like chicken; transdermal gel is applied to the inside of the ear, so he probably won't object to being dosed.
- Texas A&M University Veterinary Medicine and Biological Sciences: Cobalamin: Diagnostic Use and Therapeutic Considerations
- Broadway Veterinary Hospital: Liver Disease in Cats
- petMD: Vitamin B12 Supplementation in Pets with EPI
- Purina Care Pet Health Library: Feline Pancreatitis and Triaditis
- Veterinary Partner: Exocrine Pancreatic Insufficiency
- Wedgewood Pet Pharmacy: Vitamin B12 Deficiency in Cats
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