Feline Appetite Stimulants, Hyperthyroidism & Kidney Disease

It's a fairly common story.  My 15-year-old cat has developed hyperthyroidism and has also been diagnosed with kidney disease.  He was a 5.5kg cat about a year ago, but was now drinking a lot of water and has lost about 1.5kg, bringing his weight down to almost exactly 4kg.

His hyperthyroidism is being managed with Carbimazole, and blood tests have confirmed that the Carbimazole is working.  He isn't a candidate for either a thyroidectomy or radio iodine treatment, due to his kidney disease.  I learnt his as I was in contact with various vets, trying to work out if I can get him a better treatment than just managing his symptoms with Carbimazole.  The conclusion is that due to his kidney disease, they suspect that either treatment would result in death.

After being on Carbimazole for a couple of weeks, the cat was basically refusing to eat or would eat very little.  He would walk up to his food, sniff it, and walk away.  As such, blaming the Carbimazole for his lack of appetite, I took it upon myself to halve his dose to see if that would improve his appetite.

He was initially on a dose of 2.5mg twice a day (1/2 a 5mg tablet twice a day), which I reduced to approximately 1/4 of a tablet twice per day.  That seemed to improve things a bit, but he still wasn't eating well.  At about the 3 week mark, I called his current vet, and told them the problem and what I'd done.  Their response was that there was nothing they could dispense to help, and that if he still wasn't eating tomorrow, to bring him back in.  I wasn't happy with this response as I already knew that there were things that could be given to cats to increase their appetite, Valium for one.

I'd done some research in the past with regard to administering Valium to the cat in question, as he would occasionally get upset after having an altercation with another cat and would get fairly vocal. stop eating, and his behaviour would change - you could tell he was upset.  I found that a small dose of Valium would act a bit like a reset button, and he'd be back to normal fairly quickly.

I also found that Valium would have a few other side-effects.  Firstly, he became more affectionate and wanted more attention, his appetite would increase (usually within 45 minutes of administering the Valium) and he'd walk around like he was a bit drunk for an hour or two.  He'd be fairly floppy if you picked him up, and you'd have to put him back down carefully as he'd occasionally fall in a heap and hit his jaw on the floor.

While calling and e-mailing various vets to find out whether he would be suitable for either radio iodine therapy or a thyroidectomy, I came across one particular vet that informed me that there were two types of thyroidectomies and that she would like meet the cat and discuss his treatment options.

I figured that she just wanted to get a consultation fee out of me before giving me any information, but she was also the only vet that was willing to do a thyroidectomy if it was appropriate, and at this time, that was looking like it might be his only option.  So I took him in to see her.

The consultation was quite productive.  She had read through his medical history (15 pages to date) and went through everything relevant with me again,  I think to ensure that we were both on the same page.  I told her that I'd reduced his dose of Carbimazole to 1/4 of a tablet twice a day, and that he was eating better but still not eating well, and still not putting on any weight (but not losing weight either).  I also mentioned that he wouldn't eat the Hills Prescription Diet K/d food (it's easier on his kidneys than regular cat food).

We discussed his lack of appetite, which she explained was likely due to his kidneys not filtering his blood very well anymore, so he'd probably feel a bit like he has a hangover.  She explained that prior to getting his hyperthyroidism under control, he probably would have had high blood pressure and that would have meant more blood would be pumped through his kidneys, somewhat compensating for their inability to filter his blood properly.  She also informed me that they can give him medication to increase his appetite - pretty much the exact opposite of what his (now sacked) previous vet had advised.

I mentioned that I'd been giving him approximately 0.8mg of Valium on occasion to get him to eat, but that even that wasn't working as well as it used to and I wasn't sure if I was giving him the correct dose.  

She suggested that Mirtazapine would be another option and that it would also be better for his liver.  I was surprised to learn that Mirtazapine could be used as an appetite stimulant, and like the Valium, I already had some at home as I was prescribed it to help manage my anxiety disorder and to help me sleep, but unlike his original vet, she advised me that they can dispense Mirtazapine for the cat if I need some.

I asked if she knew what the correct dose of Valium would be to use as an appetite stimulant.  She asked her assistant to fetch "the book" and looked up the correct dose of Valium for use as an appetite stimulant: 0.2mg/kg.  So considering he was 4kg at the time, I was spot on.  She also informed me that there are other uses of Valium, and that the dose I'd been giving him was on the lower side, so a higher dose probably wouldn't have caused any harm.

The result of the consultation was a plan to feed him anything that he'll eat, try giving 1/2 a Carbimazole tablet once per day for 2-3 weeks and to give 1/4 of a 15mg Mirtazapine tablet every 3 days, then bring him back in for another blood test to see if it's working.

Approximately 3 weeks later, I took him back to his new vet.  He was weighed, heart rate checked, and they took more blood for another blood test.  The result of his blood test was that his thyroid levels were within the normal range, which was good news.  He had put on approximately 0.2kg, which was also good news, and the Mirtazapine was working better than the Valium, but it still wasn't perfect.

Administering the Mirtazapine, I found that by day 3, the cat was starting to get fussy with his food and his appetite was waining, but not always.  Sometimes he'd go the 3 days without a problem.  I asked if I could give 1/4 of a tablet every 2 days, when he occasionally stops eating.  I was advised that would be fine.

So, in summary:

This is not medical advice.  Please see your own vet for treatment options.  This is being documented here as I found it difficult to find the information online when I wanted it in the past and for my own use in the future, should I need to reference it.

0.2mg/kg is the correct dose of Valium for a cat to use as an appetite stimulant.
1/4 of a 15mg Mirtazapine tablet every 2-3 days works better than Valium for my particular cat.
1/2 a 5mg Carbimazole tablet, once per day, seems to be working better as well, even though Carbimazole is supposed to be administered twice daily.

... and I seem to have found a better vet.

The next step is a blood pressure test and somewhat optional urinalysis test to check protein levels in his urine.  The vet suspects that his protein levels are OK based on his blood test results, but would like it checked as a precaution and to have a baseline reference for use in the future.