What would you consider as the next 'lowest' dose for hyperT cat?

Re: What would you consider as the next 'lowest' dose for hyperT cat?

ChrisBVSc — Tue, 13 Jan 2015 16:06:41 GMT

Thanks for the replies. Always interesting to see what people think of this kind of scenario, because you could approach it in several different ways. I've seen cats on EOD dosing before but haven't been overly keen on the idea (same reason as Martin), however based on what Andy & Thomas are saying maybe it's not as bad as I thought. Might give it a go with this cat. Basically what I didn't want to do was swap to Felimazole (with it's benefits of easy low doses), but end up on either roughly the same dose or higher, and prolong the whole process.

Also he's definitely hyperthyroid, he actually had a unilateral thyroidectomy a couple of years ago but became symptomatic again with a T4 of 105.7 in September last year.

Re: What would you consider as the next 'lowest' dose for hyperT cat?

Thomas Johnson — Tue, 13 Jan 2015 15:47:52 GMT

[quote user="Andrew Kent"]

Hi Chris,

I would go to 10mg Vidalta every other day or adjust the dose based on food administration - is the drug currently being given with or without food? The absorption of vidalta is about 40% higher with food, so if the meds are currently being given with a meal, moving this away from the meal effectively reduces the dose by up to 40%.

I assume you are happy the cat is definitely hyperthyroid? What were the levels before treatment?

Andy

[/quote]

Or you could consider giving two 10mg Vidalta tablets over three days, with 2 days on and one day off.

Re: What would you consider as the next 'lowest' dose for hyperT cat?

Martin Atkinson — Tue, 13 Jan 2015 15:09:54 GMT

[quote user="Andrew Kent"] I am happy with EOD carbimazole and don't see it as any worse than once daily methimazole (which I thought is what you were implying earlier)[/quote]No just curious, can't argue if you've got the results to back it up.

Re: What would you consider as the next 'lowest' dose for hyperT cat?

Andrew Kent — Tue, 13 Jan 2015 14:51:01 GMT

[quote user="Martin Atkinson"]How would you know this unless you were testing every day?[/quote]

Which is what I have done - measured T4 on consecutive days to see if there is a difference.

I am not saying either is ideal and I am certainly not chasing numbers, but I am happy with EOD carbimazole and don't see it as any worse than once daily methimazole (which I thought is what you were implying earlier) and potentially better based on comparisons of half life etc.

Most owners will also go for EOD over daily if they have the choice and this cat has already been on carbimazole so we know it is tolerated.

But as I said initially I would look at dosing wrt feeding first.

Andy

Re: What would you consider as the next 'lowest' dose for hyperT cat?

Martin Atkinson — Tue, 13 Jan 2015 14:44:57 GMT

[quote user="Andrew Kent"]....this agrees with my experience with it where the T4's do not differ considerably on dosing and non-dosing days. Something like 5% of cats in one of the efficacy studies needed EOD dosing. It is a better option, for example, than once daily methimazole.[/quote]How would you know this unless you were testing every day? Without doing that I would say that IME once daily methimazole is equally efficacious. In the end it comes down once again to listening to what your patient is telling you, not chasing numbers.

Re: What would you consider as the next 'lowest' dose for hyperT cat?

Andrew Kent — Tue, 13 Jan 2015 13:55:54 GMT

[quote user="Martin Atkinson"][quote user="Andrew Kent"]I would go to 10mg Vidalta every other day [/quote] AFAIA carbimazole and methimazole compete for receptor sites of thyroid hormone, not suppress is production, so alternate day dosing is likely to see fluctuations in daily T4 which may not be helpful[/quote]

I am told that MSD have some work to show that the levels are pretty stable with EOD dosing and this agrees with my experience with it where the T4's do not differ considerably on dosing and non-dosing days. Something like 5% of cats in one of the efficacy studies needed EOD dosing. It is a better option, for example, than once daily methimazole.

Andy

Re: What would you consider as the next 'lowest' dose for hyperT cat?

Martin Atkinson — Tue, 13 Jan 2015 13:34:14 GMT

[quote user="Andrew Kent"]I would go to 10mg Vidalta every other day [/quote] AFAIA carbimazole and methimazole compete for receptor sites of thyroid hormone, not suppress is production, so alternate day dosing is likely to see fluctuations in daily T4 which may not be helpful.

As the recommended starting dose for Vidalta is 15mg and for Felimazole is 2.5mg bid that should in theory give their equivalents. So if this cat is already hypothyroid on 10mg Vidalta it would seem logical that 2.5 mg Felimazole will also be too high.However this dose may be a good starting point but don't forget you can also get 1.25mg tablets if you want to go lower and 1.25mg bid would be better than 2.5mg sid for similar reasons as my opening gambit.

Re: What would you consider as the next 'lowest' dose for hyperT cat?

Andrew Kent — Tue, 13 Jan 2015 13:12:35 GMT

Hi Chris,

I assume you are happy the cat is definitely hyperthyroid? What were the levels before treatment?

Andy

Re: What would you consider as the next 'lowest' dose for hyperT cat?

ChrisBVSc — Tue, 13 Jan 2015 13:10:48 GMT

Thanks, could be worth a try. I can't remember the last time I had to lower the dose for a cat on 10mg vidalta (possibly never!) so I'm really looking for an 'equivalent' Felimazole dose as a starting point.

Re: What would you consider as the next 'lowest' dose for hyperT cat?

Anthony Dennison — Tue, 13 Jan 2015 13:07:04 GMT

I would do things slowly. Look at 5mg felimazole in the morning, 2.5mg in the afternoon, retest and if still low to to 2.5mg BID. Best this way than allowing values to shoot up high again.