Dear Dr. John,

My cat is now an old lady of 18. She was diagnosed a few years ago as hyperthyroid and has been well regulated on medication since then. Initial attempts at giving her oral medication were impossible. As a result, my vet prescribed her a compounded transdermal paste. That has worked well since then. I just had her levels checked again and everything seems to be normal. Is it necessary to have her blood values checked twice a year? It can get a little expensive, but I want to do what is right. She also vomits occasionally. Should I be concerned about this and what could be the cause? S.A.

Dear S.A.,

I’m glad to hear that your cat has been well regulated for hyperthyroidism with medication. I suspect that you are giving her methimazole which can be given in pill form or compounded into liquid oral medication or transdermal paste. All can be effective in controlling thyroid levels in the cat. Despite the cost associated with bloodwork twice a year, it is a small expense to pay were anything else to develop. It is quite common to check the bloodwork on older cats, and dogs for that matter, twice a year that are on long term medications. The reason is simply that things do change, and adjustments to dosing may be necessary.

Additionally, any long-term medication use needs to be monitored for possible changes to the two organ systems that detoxify the body, namely the liver and kidneys since all medications are potentially toxic. As for the vomiting, if a recent examination revealed no abnormal findings on abdominal palpation and the bloodwork came back as normal then I would not be too concerned. Did you discuss this with your veterinarian? Undigested food is often vomited soon after ingestion when a cat eats too quickly. This is not uncommon in hyperthyroid cats that, prior to being medicated, likely have enormous appetites and they get in the habit of eating a lot. If the amount of vomiting increases in frequency, then it may need to be evaluated.

Dr. John de Jong is President of the World Veterinary Association. He owns and operates the Boston Mobile Veterinary Clinic and can be reached at 781-899-9994.