methimazole and side effects

[pru772]

After three doses of methimazole 2.5 mg bid, my 15 yo neutered male cat had an extreme head drop with his chin right on his chest.  He was unable to hold his head up at all.  His pupils were fixed and dilated, his gait was extremely wobbly and he seemed to navigate in bursts of energy.  I discontinued the med and the head posture returned to normal over three days.  Gait took a day or so longer and pupils started to react after five days but remain sluggish. Drug induced myasthenia gravis is described rarely in the literature.  My very experienced vet says he has never seen it.  Has anyone else?  We have restarted the med with 2 mg of prednisolone added qd and so far so good.  Make any sense to you?  Thanks

[kirsten44]

Was there ever a response to this?  My 14 year old cat was diagnosed with hyperthyroid, put on methimazole for about 2 months, and is now being tested for myasthenia gravis.  I quit the methimazole over a week ago, but symptoms have not improved.  I have other cats, so the YD diet won't work because he just goes to eat their food, and I just don't think the radiation treatment is smart in a cat his age, not to mention I do not have the money for it.  But I'd really like some hope for improvement in his ability to eat and clean himself.

[opus88]

I make a homemade diet and research the holistic route for Methylcobamamin or Vitamin B12.
the safest brand for cats is by Thorne Research #12 veggie capsules, its the purest form and has no additives that are unsafe for cats, ie: soy,  yeast and flavorings.
the recommended dosage I have found is 1/4 capsule for 1 lb of food, which breaks down to 1/16 per 4oz feeding. you would need a 1/8 of a teaspoon measurement and fill only 1/2 full.
I haven't heard of myasthenia gravis, but again follow your Vet's recommendations.
I do hope kitties recover quickly.

[felixferdinand]

I just diagnosed a cat with acquired myasthenia gravis after about 4 weeks of methimazole treatment.  I admitted the cat earlier today and had no idea why it was so weak -- blood work was unremarkable and only minimal heart disease.  Tonight I had a eureka moment as I went through a textbook and saw a one-liner about methimazole causing myasthenia.  I will withdraw the cat from the medication and see how he progresses.  I'm not sure if the owners will elect for alternative hyperthryoid therapy -- methimazole is the treatment I always use.   How did your cat fare over the next few months, Pru?