Weight-Based Levothyroxine Dosage Adjustment for Hypothyroidism

Furthermore, dose adjustments may need to be made in patients with concomitant medical conditions, in patients taking certain medications, as well as in elderly patients. Patients who have undergone any weight or hormonal changes may require dose adjustments, and the majority of pregnant women require increased doses of levothyroxine. The physician is tasked with vigilant appraisal of the patient’s status based on a thorough clinical and laboratory assessment and appropriate adjustment of their levothyroxine therapy. The patient in turn is tasked with medication adherence and reporting of symptomatology and any changes in their medical situation. The goal is consistent maintenance of euthyroidism, without the patient experiencing the adverse events and negative health consequences of under- or overtreatment.Funding Merck.Plain Language Summary Plain language summary available for this article.

Keywords relating to levothyroxine, hypothyroidism, treatment, levothyroxine dose adjustments, levothyroxine and concomitant conditions, levothyroxine and concomitant medications, and combined treatment with levothyroxine and liothyronine versus levothyroxine were searched. Potential articles of interest were identified by title and abstract, and citation lists of articles of interest were used to identify additional literature. This article is based on previously conducted studies and does not contain any studies with animals performed by any of the authors.

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Triiodothyronine, the active form of thyroid hormone, is secreted in small amounts by the thyroid but is mainly generated via extrathyroidal conversion of the prohormone thyroxine. Hypothyroidism is a common endocrine disease that requires timely and lifelong treatment since, if left untreated, it can contribute to hypertension, dyslipidaemia, and heart failure and induce reversible dementia and infertility, as well as neurosensory, musculoskeletal, and gastrointestinal symptoms 7. There is currently no other treatment for hypothyroidism, other than providing thyroid hormone replacement.

Fig.4.

As a person progresses through life, their dose may need to be adjusted because other diseases or medications can affect the dose needed for effective treatment. Pregnancy or weight gain can also affect the dose of levothyroxine needed by the patient, so patients and physicians need to work in partnership to ensure that the treatment is working as well as it can. The goal of this partnership is to maintain normal thyroid hormone levels without the patient experiencing any side effects or negative health consequences of taking too much or too little levothyroxine. Current guidelines recommend a levothyroxine dosage of synthroid europe 1.6 mcg per kg per day based on ideal body weight or lean body mass instead of actual body weight.3,4 Ideal body weight can be calculated as the weight for height that would generate a body mass index of 24 to 25 kg per m2. Lean body mass is a better predictor of the dosage requirement than actual body weight.5 Without this clarification, some patients may receive a dosage of levothyroxine that is too high. Thyroxine is actively transported to the various organs where it is converted to triiodothyronine by the activity of the deiodinases 6.

Dose Adjustment

A prospective clinical cohort follow-up study illustrated this by showing that, among 291 patients (84% females) on levothyroxine replacement therapy without a solid diagnosis of hypothyroidism and in whom the treatment was paused, 114 developed hypothyroidism, while 177 participants remained euthyroid. Hypothyroidism, a reduction in thyroid hormone levels, is one of the most common diseases worldwide. The medication most used to treat hypothyroidism is levothyroxine, a compound that acts as a replacement for a person’s thyroid hormone. People with hypothyroidism will often need to take levothyroxine for a long time, typically for the rest of their life, so it is important that their treatment is monitored closely and the dose is adjusted for the best effect as needed.

Controversies About Treatment Other Than Levothyroxine

Due to its long half-life of about 7days, in patients in the clinically euthyroid state, levothyroxine is the preferred first-line treatment for primary hypothyroidism and has been the most commonly prescribed treatment since the 1980s 8. A multivariate analysis of the results revealed that physician characteristics may affect prescription patterns, with residents of North America, for example, being more inclined to prescribe therapies incorporating liothyronine than their colleagues in Europe 85, 86. However, the study was not designed to investigate whether this was due to physician-patient interaction, specific education following the meetings, the influence of pharmaceutical companies, or media exposure, or a combination of these.

• However, in this setting, there appear to be many cases of both levothyroxine over- and under-dosing and it may be that frequent adjustments of a dose are necessary.
• The goal is consistent maintenance of euthyroidism, without the patient experiencing the adverse events and negative health consequences of under- or overtreatment.
• The goal is consistent maintenance of euthyroidism, without the patient experiencing the adverse events and negative health consequences of under- or overtreatment.Funding Merck.Plain Language Summary Plain language summary available for this article.

Other important considerations regarding levothyroxine doses in older individuals include bearing age-adjusted TSH reference ranges in mind 50 and avoiding over-replacement that might potentially exacerbate other medical conditions 8. Both of these considerations would lead to targeting of higher TSH values in older individuals (Fig. 3). Diligent monitoring of patients taking levothyroxine and regular dose adjustment to achieve optimised treatment and avoidance of adverse events are particularly emphasised.

• People with hypothyroidism will often need to take levothyroxine for a long time, typically for the rest of their life, so it is important that their treatment is monitored closely and the dose is adjusted for the best effect as needed.
• Vitamin C stands alone as an example of a supplement that may actually decrease the requirement for levothyroxine by enhancing its absorption, at least in patients with gastritis 78.
• This article is based on previously conducted studies and does not contain any studies with animals performed by any of the authors.
• When commencing levothyroxine therapy, initial dose requirements can vary greatly from small doses such as 25–50 μg in an individual with mild or subclinical disease, where the therapy may be supplementing endogenous function, to larger doses of 88–175 μg in cases of patients with negligible endogenous thyroid function.

When Levothyroxine Administration Is a Necessity

The dose of levothyroxine required by a patient following thyroidectomy can be predicted by either body weight or body mass index (BMI) 10–12. Body weight, BMI, ideal body weight, and lean body mass can all predict the initial dose requirement, with the latter three parameters providing the more accurate estimates 10, 13. These range from simple formulae based only on body weight or BMI to more complex formulae that also incorporate other factors such as patient sex 10, 14. Generally, both a TSH-based estimate and a body weight-based estimate yield similar initial estimates of dose requirement (Fig. 1). Currently, there is no clear, high-level guideline on how to best adjust the starting dosage in patients with a body mass index greater than 30 kg per m2. Monitoring TSH levels every six to eight weeks and adjusting levothyroxine dosages until the TSH reaches goal are critical to avoid iatrogenic hyperthyroidism or under-replacement.

• Current guidelines recommend a levothyroxine dosage of 1.6 mcg per kg per day based on ideal body weight or lean body mass instead of actual body weight.3,4 Ideal body weight can be calculated as the weight for height that would generate a body mass index of 24 to 25 kg per m2.
• The acidity of the thyroxine molecule, which caused diminished absorption resulting in low bioavailability, was an unresolved problem for more than 20 years following its discovery 3.
• Monitoring TSH levels every six to eight weeks and adjusting levothyroxine dosages until the TSH reaches goal are critical to avoid iatrogenic hyperthyroidism or under-replacement.
• A multivariate analysis of the results revealed that physician characteristics may affect prescription patterns, with residents of North America, for example, being more inclined to prescribe therapies incorporating liothyronine than their colleagues in Europe 85, 86.
• Calcium supplements 74, 75 and iron 76, 77 also reduce absorption and thereby increase the levothyroxine dose requirement or increase serum TSH 52, 53.

Calcium supplements 74, 75 and iron 76, 77 also reduce absorption and thereby increase the levothyroxine dose requirement or increase serum TSH 52, 53. Vitamin C stands alone as an example of a supplement that may actually decrease the requirement for levothyroxine by enhancing its absorption, at least in patients with gastritis 78. Its chemical structure was determined in 1926 by Harington, and it was synthesised in 1927 by Harington and Barger 1, 2.

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As levothyroxine is usually administered over a patient’s lifetime, physiological changes throughout life will affect the dose of levothyroxine required to maintain euthyroidism. The physician is tasked with vigilant appraisal of the patient’s status based on a thorough clinical and laboratory assessment and appropriate adjustment of their levothyroxine therapy. The goal is consistent maintenance of euthyroidism, without the patient experiencing the adverse events and negative health consequences of under- or overtreatment. When commencing levothyroxine therapy, initial dose requirements can vary greatly from small doses such as 25–50 μg in an individual with mild or subclinical disease, where the therapy may be supplementing endogenous function, to larger doses of 88–175 μg in cases of patients with negligible endogenous thyroid function.