Metformin-induced thyrotropin suppression is not associated with cardiac effects

Abstract

OBjECTIVE: Metformin treatment may induce a decrease/suppression in serum TSH levels, mimicking sub-clinical hyperthyroidism (SHT). The aim of the present study was to retrospectively evaluate changes in several electrocardiographic indices in euthyroid subjects with diabetes who, after starting metformin treatment, developed a low serum TSH as compared to patients with SHT resulting from an underlying thyroid disease or TSH suppressive treatment with L-thyroxine. DEsIGn: Heart rate, P wave duration, P wave dispersion, Qtmax, Qtmin and Qt-dispersion were assessed in 23 patients with diabetes treated with metformin before and after 6 months of tsH-suppression and in 31 control patients with sHt. REsuLts: No significant changes in electrocardiographic parameters were observed from baseline to the TSH-suppression measurement. A significant difference in P wave duration (102.9±7.4 vs. 92.1±5.8 ms, p<0.001), P wave dispersion (13.1±3.4 vs. 7.1±3.5 ms, p<0.001), Qtmax (399±18 vs. 388±16 ms, p=0.024), Qtmin (341±14 vs. 350±17 ms, p=0.038) and Qt dispersion (49.9±9.6 vs. 30.9±9.2 ms, p<0.001) were observed between the control group with SHT and the group of diabetic patients with low serum levels of tsH. COnCLusIOns: Our results show that the TSH-suppressive effect observed in patients taking metformin is not associated with peripheral markers of thyroid hormone excess, at least at the cardiac level.

Metformin and low levels of thyroid-stimulating hormone in patients with type 2 diabetes mellitus

“…In a recent study, 23 patients in whom low TSH levels developed while they were taking metformin did not exhibit the expected changes to heart rate and electrocardiographic parameters as patients with subclinical hyperthyroidism. 27 However, the conclusions of this study are limited by its small sample and lack of adjustment for potential confounders. Given the relatively high incidence of low TSH levels observed in our study in patients receiving metformin (125.2/1000 person-years), there is a need for further research to determine the short-and longterm clinical consequences of this biochemical event, the necessity of monitoring TSH levels when starting metformin, and the appropriateness of adapting levothyroxine doses when low TSH levels are observed in patients starting metformin.…”

The Effect of Metformin on the Hypothalamic-pituitary-thyroid Axis in Patients with Type 2 Diabetes and Subclinical Hyperthyroidism

“…However, in this group of patients, metformin did not produce any significant changes in serum levels of free thyroxine and triiodothyronine [7][8][9][10]. Despite a reduction in TSH, metformin-treated patients did not develop clinical symptoms of hyperthyroidism [11]. Unfortunately, to achieve maximum clinical benefits, metformin is often administered at much higher doses than those used in these studies.…”

The Effect of Metformin on Hypothalamic-Pituitary-Thyroid Axis Activity in Women with Interferon-Induced Hypothyroidism: A Pilot Study

“…This decrease in thyrotropin should in part be attributed to the impact of metformin on dopaminergic regulation of thyrotropin secretion [17]. Despite a decrease in thyrotropin, metformintreated hypothyroid patients did not develop clinical symptoms of hyperthyroidism [19]. However, in patients with hyperthyroidism, thyrotropin-lowering effect of metformin was only slight and transient [20], while in euthyroid patients metformin produced no effect on serum levels of this hormone [13,16,21].…”