How accurate is dosing Levothyroxine by body weight?

[Joesmum]

I read that we should be dosing Levothyroxine 1.6mcgs X body weight in kilos.

Does this achieve accurate results and has Thyroid UK ever collected that data from its subscribers to test the theory?

Many thanks

[diogenes Remembering]

This is only one number of a range 1.6-1.9. Other important factors include obesity and age. Whereas this range is adequate for most, it may not be for all. It certainly can't be used in combination therapy.

[Joesmum in reply to diogenes]

thank you.

I am about 92kgs and on both T4 and T3.

150 mcg Levo and 20mcgs T3

I still have no hunger. My weight is catastrophic. I was concerned by what I’d read about the 1.6 for thank you for clarifying.

[SeasideSusie Remembering]

Joesmum

I read that we should be dosing Levothyroxine 1.6mcgs X body weight in kilos.

If you are referring to the NICE guidelines, it is listed as one suggestion that some people are started on this dose when initially diagnosed as one option for treatment.

cks.nice.org.uk/topics/hypo...

Initiation and titration

The dose of levothyroxine (LT4) should be individualized on the basis of clinical response and thyroid function test (TFT) results. Treatment must be monitored regularly to determine an adequate dose and to avoid both under- and over-treatment.

The NICE clinical guideline recommends:

* Consider starting LT4 at a dosage of 1.6 micrograms per kilogram of bodyweight per day (rounded to the nearest 25 micrograms) for adults under 65 years of age with primary hypothyroidism and no history of cardiovascular disease.

* Consider starting LT4 at a dosage of 25–50 micrograms per day with titration for adults aged 65 years and over, and adults with a history of cardiovascular disease.

The British National Formulary (BNF) recommends:

* For adults aged 18–49 years — initially 50–100 micrograms once daily; adjusted in steps of 25–50 micrograms every 3–4 weeks, adjusted according to response; maintenance 100–200 micrograms once daily.

* For adults aged 50 years and over, with cardiovascular disease, or severe hypothyroidism — initially 25 micrograms once daily; adjusted in steps of 25 micrograms every 4 weeks, adjusted according to response; maintenance 50–200 micrograms once daily.

It's an option, it's not set in stone, it's a starting point subject to adjustment. If it works for some people it's a happy coincidence, it doesn't work out that everyone's dose needs to be 1.6mcg Levo per 1kg weight.

[Joesmum in reply to SeasideSusie]

Thank you so much.

I am now 14.5st or 92kg and am currently taking 150 mcgs Levo and 20mcgs T3 which is an awful lot more than the guidelines.

This illness has had a catastrophic effect on my weight.

I was just concerned that’s all.

[helvella Administrator]

You might care to look at what I have written about this approach.

helvella's calculation document and spreadsheet can be can be found by following this link:

helvella - Estimation of Levothyroxine Dosing in Adults

A discussion about the use of formulas to estimate levothyroxine dosing. Includes link to a downloadable spreadsheet which calculates several of these.

helvella.blogspot.com/p/hel...

[Joesmum in reply to helvella]

thank you so much that makes for interesting reading.

[SlowDragon Administrator]

What were most recent Ft4 and Ft3

Last dose levothyroxine 24 hours before test

Day before test ALWAYS split T3 as 3 smaller doses spread through the day with last 5mcg dose Approx 8-12 hours before test

Do you always get same brand levothyroxine and same brand T3

Essential to have optimal vitamin levels for levothyroxine or T3 to work

When were vitamin D, folate, ferritin and B12 last tested

What vitamin supplements are you taking

[Happyfairy09]

I normally dose my levo & ndt to how I feel. Interesting to hear about dosing by body weight, following this closely.

[SeasideSusie Remembering in reply to Happyfairy09]

Happyfairy09

It's not in the guidelines to dose by body weight. It's a method of starting dose for new hypo patients, then the dose is adjusted according to the individual's needs. It's not meant to be anything other than a starter dose, and not meant as a guide for the patient to be dosed according to weight going forward.

[roukounasGK]

I have read somewhere (i dont remember where but i am fairly certain it was from a md paper) that this is 1.6 x bodyweight in kg for the optimal BMI, not your actual weight. This essentially means somewhere around 24 to 25. So you calculate which is the optimal weight, based on a bmi value of 24 and calculate the dose based on this times 1.6. I always found that 1.6 x actual weight was too much a dose so this seems legit.