Levothyroxine dosage

[Alos]

I am a 29year old female weighing 70.4kg with height of 1.67m. Kindly advise on how to calculate the levothyroxine dosage. Thanks

[humanbean]

See this link (sorry, it is heavy going...) :

uspharmacist.com/continuing...

There are a couple of paragraphs just after Table 4 that discuss levo dosing by weight, but it is worth reading more of it than just this :

" The initial dosage of levothyroxine for adults is dependent on several clinical issues. Infants and children have different requirements for thyroid replacement. The dosage, on a microgram per kilogram basis, is higher and must be replaced in a timely manner to avoid irreversible consequences. This topic will not be discussed here and the following dosage recommendations are to be considered only for patients over the age of 18. If the patient is between 18 and 50 years old and in relatively good health without any risks for coronary heart disease (CAD), the initial dose for overt hypothyroidism is based on the complete replacement dose.

Most patients will require between 1.6 to 1.8 mcg of levothyroxine per kilogram of ideal body weight. A woman weighing 110 lbs (50 kg) could be started on 75 or 88 mcg daily. If the patient is not in good health with evidence of CAD, the initial dose could be as low as 12.5 to 25 mcg/day, and titrated very cautiously. Patients over the age of 50, even without a documented history of ischemic heart disease, should be started on a low dose of levothyroxine and monitored closely."

Note that it refers to the patient's ideal body weight as the basis for calculating dosage, not actual body weight.

[Hidden in reply to humanbean]

What are the irreversible consequences referred to?

[humanbean in reply to Hidden]

Take a look under "Prognosis" in this link :

patient.co.uk/doctor/childh...

[Elven in reply to humanbean]

That link seems to lead to a discussion of childhood and congenital thyroid disease. Not adult?

[humanbean in reply to Elven]

In the quote I gave above in italics, the irreversible consequences referred to are specifically in connection with infants and children, not adults.

Infants and children have different requirements for thyroid replacement. The dosage, on a microgram per kilogram basis, is higher and must be replaced in a timely manner to avoid irreversible consequences.

The consequences of non-treatment of adults are normally slower to manifest themselves, and would usually be considered to be less urgent than treatment of babies and children.

For example, in Victorian times in England, babies born with no thyroid or a barely functioning thyroid or born to mothers who were hypothyroid would either die or would suffer from what was known as "cretinism".

en.wikipedia.org/wiki/Creti...

No doubt there are parts of the world now where this still happens.

So, that was why I linked to something about thyroid issues in infants and children.

[Elven in reply to humanbean]

Ah. Gotcha! x

[helvella Administrator in reply to humanbean]

I hope the rest of the article has been more thoroughly written and proof-read than the table headed Levothyroxine Doing (Adults).

Rod

[humanbean in reply to helvella]

It's only a teaching aid. Perhaps the spelling errors are to keep the students awake and to see if they are paying attention.

[helvella Administrator]

There are many formulas for calculating dose required in the case of going straight to full replacement. That would typically occur when someone has a total thyroidectomy.

Indeed, I have created a spreadsheet for precisely this purpose. It is based on published information (references included). However, as the formulas all come out with different results, you should draw the obvious conclusion that none of them is better than an educated guess.

ALL dosing requires to be reconsidered in the light of experience, blood tests, symptoms, etc. NONE of it is an automatic "dial-a-dose". The are so many factors that confound a simplistic approach - starting with the formulation of the tablets and going through all the issues of absorption, ....

Feel free to download my spreadsheet - I think it will work in most halfway decent spreadsheet programs like Excel and OpenOffice/Libre.

dl.dropboxusercontent.com/u...

Rod

[Clutter]

Alos, I think the weight/dose ratio is only calculated when patients are starting Levothyroxine after thyroidectomy. The usual starting dose is between 50-100mcg for adult patients under 50 years of age without heart disease which is then titrated according to TSH blood test and, if you're lucky, according to symptoms.

[Alos]

Thanks guys. I actually had a total thyroidectomy 2years ago and I've still been unable to get my TSH within normal range and my GP keeps saying be patient but it's frustrating you know

[Alos]

Thanks helvella, actually agree as the results are different. I just wish I cld get it right at the snap of my fingers.