Hyperthyroidism

Hello, My 16 year old cat was diagnosed with hyperthyroidism a few weeks ago, I started giving him Thyronorm which was fine to start with but after 2 weeks he’s started being sick a lot and hasn’t eaten much. I took him back to the vets and they gave him an anti sickness injection and said if he doesn’t improve in a few days they can switch his medication to Methimazole that I would rub on his ear. They said it’s harder to get the dosage right with this etc. My question is, does the sickness normally subside with the Thyronorm, is so after how long? Are there any other options to treat this as it’s breaking my heart seeing him so sick and not himself. Many thanks Mel

Hello and thankyou for this question.   The datasheet for Thyronorm (a dense sheet of text which ought to be supplied with the drugs but is also online) states that one to ten animals in 1000 show side effects that might include anorexia (not eating at all), inappetence and lethargy, which would resolve 7-45 days after stopping therapy.  Other causes can include over-correction of thyroid hormone, sending the thyroid hormone levels too low, or concurrent illness.  However, in many cases of the initial side effects, the signs may be mild and transitory and may not be a reason for withdrawing treatment.  The data sheet does not give a length of time, but your vet could speak to a drug company representative on your behalf about making decisions.   Their role is in keeping your cat safe, which may involve examining their hydration, doing tests (as suggested in the data sheet), changing therapy or even giving fluids if necessary.  Therefore, please keep them updated during this delicate transition period, so that they can recommend any changes necessary for your cat in their particular unique set of circumstances.  Wishing you all the best.