On carbimazole, dosing query

[MissZP]

Hi there, recently diagnosed with hyperthyroid, July. Started off on a 20mg dose daily 1x20mg tablet. Last week dose increased to 30mg daily, 1x20mg and 2x5mg, because levels dropped from free T4 88 to 35 but have stated to creep up again. Whilst looking through message boards I've heard people talking about dividing their dose. Dr hasn't given me any instructions on how to take the tablets and I'm still waiting to see an Endo. I've been very lethargic lately and just wondered is there anything to be gained from diving the dose. Any information gratefully received.

Thanks Zoe

[helvella]

It is expressly stated on the Summary of Product Characteristics document for Concordia's product:

Adults

The initial dose is in the range 20 mg to 60 mg, taken as two to three divided doses.

medicines.org.uk/emc/medici...

And, slightly less obviously, in the Patient Information Leaflet:

• The tablets you take each day may be split into two (morning and evening) or three (morning, afternoon and night). Ask your pharmacist if you are not sure.

medicines.org.uk/emc/PIL.27...

Why do we repeatedly see doctors ignoring documented advice?

There is a good technical reason to split dose. The half-life of carbimazole in the human body is short. If you only take it once a day, your thyroid can start producing more thyroid hormone before you take your next dose when the amount in your bloodstream drops. Splitting helps to keep the level high enough to be effective throughout the day.

[MissZP in reply to helvella]

Hi helvella,

Thank you for your speedy reply. Reading about the half life of the drug is what prompted me to ask the question. Thank you for your detailed response. Maybe this would explain why I've had to increase my dose? I'll try splitting the dose into 10mg and see how I get on at the next blood test. If it works better maybe they could prescribe be just 5mg tabs instead of the 20s and 5s. You kind of assume that a dr would tell you how to take the tablets, my instructions just say 'daily'.

Thanks for your help.

[helvella in reply to MissZP]

MissZP,

I might once have made assumptions about prescribing competence and issuing instructions - but not no more.

[Rmichelle in reply to helvella]

Hope you dont mind me jumping your post missZP.XX

[Rmichelle in reply to helvella]

Hi hevella can i ask i am going to start taking my carbimazole in 2 doses starting tomorrow instead of one 20mgs, endo wants to start titration. What time of night can i take it or would it hurt to take it early around 7 if first dose is 8.30am.xx

[helvella in reply to Rmichelle]

Rmichelle,

Whilst perfectly happy for you to ask, please do remember I have no personal experience nor medical training!

However, I don't think it would make any measurable difference taking it a bit early or a bit late.