The effect of metformin on the hypothalamic-pituitary-thyroid axis in patients with type 2 diabetes and amiodarone-induced hypothyroidism.

Background: Chronic metformin treatment was found to reduce elevated thyrotropin levels. Amiodarone treatment is associated with a range of effects in thyroid function from mild derangements to overt thyroid dysfunction. No previous study has investigated the effect of metformin on hypothalamic-pituitary-thyroid axis activity in patients with amiodarone-induced hypothyroidism.
Methods: The study included three age-, sex- and weight-matched groups of amiodarone-treated patients with type 2 diabetes: patients with treated overt hypothyroidism (group I, n=15), patients with untreated subclinical hypothyroidism (group II, n=15), and subjects without thyroid disorders (group III, n=18). The lipid profile, fasting plasma glucose levels, the homeostatic model assessment 1 of insulin resistance ratio (HOMA1-IR), glycated hemoglobin, the estimated glomerular filtration rate, as well as serum levels of thyrotropin, thyroid hormones, prolactin, insulin and insulin-like growth factor-1 (IGF-1) were assessed at baseline and after 6 months of metformin treatment (2.55-3g daily).
Results: In all groups of patients, metformin reduced plasma glucose and triglycerides, serum insulin, glycated hemoglobin as well as HOMA1-IR. The estimated glomerular filtration rate, thyroid hormones, prolactin and IGF-1 remained at a similar level throughout the study. In patients with untreated amiodarone-induced hypothyroidism, but not in the other groups of patients, metformin reduced serum levels of thyrotropin and this effect correlated weakly with its action on insulin sensitivity.
Conclusions: The obtained results indicate that the effect of metformin on hypothalamic-pituitary-thyroid axis activity is partially related to thyroid function. Metformin treatment may bring clinical benefits to patients with amiodarone-induced hypothyroidism and poor tolerance of exogenous L-thyroxine.
(Copyright © 2015 Institute of Pharmacology, Polish Academy of Sciences. Published by Elsevier Urban & Partner Sp. z o.o. All rights reserved.)