Daily dosing on Thiamazole

RE: Daily dosing on Thiamazole

George Cooper — Sat, 17 Dec 2022 15:07:06 GMT

My preference for 20+ years was always to opt for surgery - and this was followed by patients that did exceptionally well indeed.

One extraordinary occasion (in a practice where I did a weekly locum and where the "Gold Standard" as they saw it was de rigeur) I was ticked off for arranging excision soon after seeing the cat. The owner - a middle aged lady - produced her mobile and asked me to repeat all I had said to her husband where I pointed out all the pros and cons as I saw it. He listened in rapt attention (I thought) and at the end asked a couple of questions before announcing that he agreed with everything I had said. "Oh", he said, "and by the way, I am a human thyroid surgeon!"

RE: Daily dosing on Thiamazole

Rob Loxley — Sat, 17 Dec 2022 09:37:01 GMT

[quote userid="8991" url="~/001/veterinary-clinical/small-animal/medicine/f/discussions/30513/daily-dosing-on-thiamazole/240265#240265"]Funny old disease hypert4 - i remember Malcolm Ness on here saying he regarded it as a surgical disease where goitre was present, and I tend to agree (although radioiodine is probably the best treatment but still expensive for most clients).[/quote]

Agree, at the moment the only place nearish us taking cases for I131 is the RVC and their waiting list extends to late 2023 it seems! We still do lots of thyroidectomies and good success overall; if you stabilise to euthyroid and they're stable preop then there shouldn't be any surprises after 'permanent' treatment. We do have lots of clients who prefer longterm medical treatment (and I think the ease of dosing thyronorm liquid compared to administering tablets has supported this), but we do as a result seem to see a number having to go up to huge doses of medication progressively over time (have these become resistant or transformed to carcinomas?).

RE: Daily dosing on Thiamazole

Neil Wheadon — Fri, 16 Dec 2022 11:55:13 GMT

[quote userid="8991" url="~/001/veterinary-clinical/small-animal/medicine/f/discussions/30513/daily-dosing-on-thiamazole/240272#240272"]I'm wracking a foggy brain here but I thought Tim Williams had done some work on this at the RVC (funnily enough using PDSA patients) and found that 'unmasking' renal disease didn't alter survival and those undertreated for hypert4 did worse overall. [/quote]

This was the opinion I seemed to get from the CPD I have just done

Below is the slide from the presentation (it's a bit foggy) but the reference is there

Williams et al JVIM 2010

RE: Daily dosing on Thiamazole

David Mills — Fri, 16 Dec 2022 11:47:33 GMT

Hi Ian, ha we don't mind medics commenting (sometimes)

Yes I'm not sure either but one thing I hear commonly is that surgery is 'permanent' and 'what if they have renal disease?' (same is obviously true for radio-iodine). I recently discussed this with medical colleagues and there was a smorgasboard of opinion. I thought that the 'balancing' of renal dz vs hypert4 was a little historic and the current thinking was that we should treat the hypert4 as this is more likely to cause a) clinical signs b) reduce survival? I'm wracking a foggy brain here but I thought Tim Williams had done some work on this at the RVC (funnily enough using PDSA patients) and found that 'unmasking' renal disease didn't alter survival and those undertreated for hypert4 did worse overall.

Musing - if a cat has renal disease, they have renal disease - hypert4 doesn't change this, it just makes the lab numbers look better from increased GFR?

Would be interested to hear your thoughts

David

RE: Daily dosing on Thiamazole

Ian Ramsey — Fri, 16 Dec 2022 09:27:37 GMT

Hi David,

Why this surgery is so uncommonly performed now (compare the results from 2 studies - admittedly different populations - UK vs Australian but also 5 years apart) is a bigger question than I can answer because I suspect it is part of the general move away from attempting surgery. I know I am not supposed to say things like this being a medic but this is disappointing because the results of surgery are - as you note - generally very good.

Ian

Higgs P, Murray JK, Hibbert A. Medical management and monitoring of the hyperthyroid cat: a survey of UK general practitioners. J Feline Med Surg. 2014 Oct;16(10):788-95. doi: 10.1177/1098612X13519633. Epub 2014 Jan 14. PMID: 24423813.

Kopecny L, Higgs P, Hibbert A, Malik R, Harvey AM. Management and monitoring of hyperthyroid cats: a survey of Australian veterinarians. J Feline Med Surg. 2017 Jun;19(6):559-567. doi: 10.1177/1098612X16634392. Epub 2016 Mar 10. PMID: 26965675.

RE: Daily dosing on Thiamazole

David Mills — Fri, 16 Dec 2022 00:23:17 GMT

i remember a few moons ago CPD on Felimazole by the pharma company saying it could be given once daily effectively but would take slightly longer to stabilise. After all, we are always ultimately talking about the same drug - Vidalta (licensed SID) is metabolised to methimazole as the active ingredient.

Funny old disease hypert4 - i remember Malcolm Ness on here saying he regarded it as a surgical disease where goitre was present, and I tend to agree (although radioiodine is probably the best treatment but still expensive for most clients). I remember writing a clinical abstract on this many years ago and most unilateral thyroidectomy cats were symptom free for a median of 4y (n=113) and at least a third died of other causes anyway. The ectopic thyroid issue is always raised but a lot of the studies at the time were based on immunofluorescence or similar and the clinical effects were uncertain; however I stand to be corrected on these aspects as it's a while since I looked at them.

RE: Daily dosing on Thiamazole

Ian Ramsey — Thu, 15 Dec 2022 13:42:06 GMT

The paper that originally looked at this (Trepanier et al 2003) showed a clear advantage of starting therapy twice daily. This study demonstrated that euthyroidism can be reached using methimazole once daily in 71% of 17 cats but only after 4 weeks, while 87% of 15 cats were euthyroid after 2 weeks of twice a day dosing. The reason for this may well be due to gastrointestinal transit time which is shorted in untreated hyperthyroid cats. As a result less of the drug is absorbed. However clinical experience shows that longer term once daily is effective (Daminet et al 2013) So once you have achieved satisfactory control then transit time is longer so there is more time for the cat to absorb the drug. So encouraging owners to start twice daily but with the promise that this will only be for the first 2 weeks seems to be the best balance to me.

It has been suggested by one manufacturer (following a freedom of information request in the USA) that a dose of 2·5 mg twice a day is associated with less serious side-effects than 5 mg once a day - so switching to once daily and increasing the dose is probably less good. However owner compliance may be better....

Of course no discussion on this would be complete without saying that (even with a short term supply issue we have at the moment) radio-iodine is likely to be better in terms of long term survival and less side effects anyway :-) - and may well work out cheaper in the long run (depending on how much you charge for methimazole and how much monitoring you do. Surgery is also a useful alternative and should normally be cheaper even in the medium term.

Best wishes

Ian

Trepanier LA, Hoffman SB, Kroll M, Rodan I, Challoner L. Efficacy and safety of once versus twice daily administration of methimazole in cats with hyperthyroidism. J Am Vet Med Assoc. 2003 Apr 1;222(7):954-8. doi: 10.2460/javma.2003.222.954. PMID: 12685785.

Daminet S, Kooistra HS, Fracassi F, Graham PA, Hibbert A, Lloret A, Mooney CT, Neiger R, Rosenberg D, Syme HM, Villard I, Williams G. Best practice for the pharmacological management of hyperthyroid cats with antithyroid drugs. J Small Anim Pract. 2014 Jan;55(1):4-13. doi: 10.1111/jsap.12157. Epub 2013 Dec 27. Erratum in: J Small Anim Pract. 2014 Mar;55(3):179. PMID: 24372075.

RE: Daily dosing on Thiamazole

Beats — Wed, 14 Dec 2022 14:39:43 GMT

My understanding is similar to Rob's.

I think on both your points, Neill, these are matters of opinion, with others taking an opposite opinion, e.g. for "balance"

https://youtu.be/wsVr1VDKRQQ

Personally, I tend to give felimazole most often, starting 5mg daily to averaga cat and then often take out the biggest goitre and see where we're at after a few weeks. Weight is biggest feature for me.

RE: Daily dosing on Thiamazole

Rob Loxley — Wed, 14 Dec 2022 13:45:06 GMT

Weve had plenty of cats on once daily felimazole, the data sheet does support this; my understanding is that the biological activity time exceeds the drug half-life; understanding is also that they can however take longer to stabilise by a week or 2 than those on twice daily, on higher doses I do try to split to twice daily