Endocrine Abstracts

Background: Recent studies suggest that metformin (MF) may reduce TSH concentration. This fact could imply a dosage reduction of levothyroxine among those hypothyroid patients taking metformin.

Aim: To determine, in a retrospective analysis, the impact of metformin in thyroidectomized patients (a condition not influenced by endogenous thyroid hormone production) on levothyroxine replacement.

Patients and methods: One hundred ninety two subjects underwent total thyroidectomy. Patients were divided into two groups depending on MF use: group A, without metformin (159 patients: 134 women; 52 (15.7) years old, 70.2 (13.5) kg of weight, 56 of them affected with differentiated thyroid cancer (DTC)), and group B, with metformin (33 patients: 24 women; 63 (9.8) years old, 79.3 (13.9) kg of weight, nine cases with DTC). Replacement dose was properly adjusted in all patients. Levothyroxin requirements were compared between groups.

Results: TSH levels did not show statistically significant differences between the groups: TSH 0.67 (0.11–2.81) mU/l in group B and 0.80 (0.11–4.28) mU/l in group A; P value=0.46. No differences on total levothyroxine dosage were found: 114 (100–150) μg in group A vs 125 (100– 142) in group B; P value=0.9. However, when calculating the weight adjusted levothyroxine dose (μg/kg) significant differences were evidenced: 1.66 (1.38–2.08) μg/kg in group A vs 1.53 (1.26–1.70) in group B; P value=0.010.

Conclusions: Thyroidectomized patients on metformin treatment do need lower thyroxine dose per kilogram.