Hyperthyroidism v. kidney failure

Last January I posted regarding our almost-16 years old cat, Toby,
being diagnosed with hyperthyroidism. His T4 reading was 287 at that
time, his weight had dropped from 6kg to 3.5kg and his appetite was
poor.

My vet prescribed Felimazole initially, 1 tablet twice a day and after
two weeks his appetite had improved and he had gained some weight.
Two weeks further on, his weight had risen further and his appetite
was still reasonably good. However, he was drinking a phenomenal
amount and his urine output was copious. I also noticed that he seemed
cold and the inside of his mouth was very pale. The vet said that he
was anaemic and further blood tests showed that his T4 had dropped to
5 and his kidney enzymes had increased. Felimazole was reduced to 1
tablet a day. He started to feel warmer and his mouth pinked up,
although his appetite dropped back again. His drinking and urination
returned to normal. One week later he had a repeat of the blood tests
which showed that his T4 had risen to 88 but his kidney enzymes were
still high. As he seemed especially sensitive to the Felimazole, he
was prescribed Neo-Mercazole instead at a very low dosage of half a
tablet twice a day. The vet also recommended putting him on a special
kidney diet.

After his second dose of Neo-Mercazole he vomitted (something very
rare with Toby) and he would not eat the new food. The vet said to
stop giving him the Neo-Mercazole, and, as not eating was very bad for
his kidneys, let him go back to his normal diet. Two weeks later his
weight had dropped again and his appetite was poor. His heart rate
was high at about 184 beats per minute while resting, although at the
vet clinic it climbed to 256. So the vet gave him an anabolic steroid
injection to boost his appetite, plus prescribing Fortekor (which is
not licensed in the USA but contains - if that`s the right word -
benazepril) to help his kidneys and also increase his appetite. At
the
same time, we were to resume giving Toby the Neo-Mercazole at the same
rate as before. This was two days ago and until this afternoon he
hadn`t had a bowel movement and his appetite had dropped even further.
Today the vet advised me to stop the Neo-Mercazole but to continue
with the Fortekor.

I do not know if not giving him the Neo-Mercazole made the difference,
but this evening he had a very good bowel clear out and his appetite
was a little better, although he is not eating sufficient to maintain
his body weight even without the complication of the hyperthyroidism.

So, we have a dilemma : if we continue to treat his hyperthyroidism
his
kidneys will pack up, but if we do not treat the hyperthyroidism he
will develop heart failure, or perhaps have a stroke. I get the
impression that the vet has not come across such a difficult cat to
treat for hyper-t and is struggling to find a regimen that will help
without compromising his kidney function. If anyone has any hints,
tips, or clues as to what we could try next, I would be most grateful.

Many thanks
Kate