Dosis de levotiroxina varía según la etiología del hipotiroidismo y el peso corporal

Objetivo: Determinar las dosis de levotiroxina necesarias para alcanzar control bioquímico del hipotiroidismo según su etiología, peso corporal, TSH inicial y tiempo desde su diagnóstico.
Población y métodos: Estudio de cohorte retrospectivo en pacientes hipotiroideos mayores de 14 años con control bioquímico de la enfermedad.
Resultados: Se incluyeron 518 pacientes, 90% mujeres. El hipotiroidismo primario fue la forma más común (66,3%), seguido por el hipotiroidismo postiroidectomía total (13,1%), poshemitiroidectomía (6,1%), central (5,9%), posyodo radioactivo (5,7%) y postiroiditis subaguda (2,5%). Los requerimientos respectivos de levotiroxina (µg/kg/día) en ese mismo orden fueron: 1,07± 0,48, 1,65± 0,46, 1,11± 0,52, 1,33± 0,6, 1,51± 0,58 y 1,11± 0,72 (p<0,001). La dosis necesaria en pacientes con hipotiroidismo primario se incrementó con el paso del tiempo desde el diagnóstico: menos de 2 años: 0,77 ± 0,38, entre 2 y 5: 0,90 ± 0,40, mayor de 5: 1,07 ± 0,48 (p<0,001).
En pacientes con TSH inicial menor de 10 mUI/L y con menos de dos años de evolución se normalizó la TSH con dosis de 0,65 µg ± 0,33, mientras aquellos con TSH inicial mayor de 20 necesitaron 1,34 µg ± 0,68. (p<0,001). Se observó una diferencia significativa en las dosis requeridas para lograr control de la enfermedad de acuerdo con el índice de masa corporal, siendo menores por kilo de peso a mayor grado de sobrepeso/ obesidad (p = 0,0067).
Conclusión: La dosis requerida de levotiroxina para alcanzar el control bioquímico depende de la etiología de la enfermedad, de los valores de TSH al momento del diagnóstico, del peso y el tiempo de evolución del hipotiroidismo. La dosis necesaria para el control de formas leves/tempranas es menor que la recomendada en ausencia de función residual.

Abstract
Objective: To determine the dose of levothyroxine needed to achieve biochemical control of hypothyroidism based on etiology, body weight, baseline TSH and time since diagnosis.
Population and methods: Retrospective cohort study with hypothyroid patients 14 years of age and older with biochemical control of the disease.
Results: 518 patients were recruited, 90% of them women. Primary hypothyroidism was the most common form (66.3%), followed by hypothyroidism post-total thyroidectomy (13.1%), post hemi-thyroidectomy (6.1%), central (5.9%), post-radioactive iodine treatment (5.7%), and post thyroiditis (2.5%). The respective levothyroxine requirements (µg/kg/d) in the same order were:
1.07 ± 0.48, 1.65 ± 0.46, 1.11 ± 0.52, 1.33 ± 0.6, 1.51 ± 0.58 and 1.11 ± 0.72 (p <0.001). The required dose in patients with primary hypothyroidism increased as a function of time since initial diagnosis: Less than 2 years: 0.77 ± 0.38, 2 to 5 years: 0.90 ± 0.40, more than 5 years: 1.07 ± 0.48 (p <0.001).
In patients with baseline TSH levels lower than 10 mIU/L and less than 2 years of evolution, TSH was normalized with doses of 0.65 µg ± 0.33, whereas those with baseline TSH levels higher than 20 needed 1.34 µg ± 0.68 (p <0.001). A significant difference was observed in the dose required to achieve disease control. This difference was related to body mass index, as follows: The greater the degree of overweight/obesity, the lower the doses needed per kg of body weight (p = 0.0067).
Conclusion: The dose of levothyroxine required to achieve biochemical control depends on the etiology of the disease, TSH levels at the time of diagnosis, weight, and time since onset of hypothyroidism. The dose required to control mild and early forms is lower than the dose recommended in the absence of residual function.

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Hipotiroidismo
dosis levotiroxina
tratamiento
hypothyroidism
dose levothyroxine
treatment