Serial Changes of Liver Function Tests before and during Methimazole Treatment in Thyrotoxic Patients

Abstract

Overt hyperthyroidism and methimazole (MMI) treatment are frequently associated with abnormal liver function tests (LFTs). We describe the serial changes of LFTs in MMI-treated hyperthyroid patients. We retrospectively analyzed all 77 patients presenting with newly diagnosed overt hyperthyroidism (59 Graves diseases, 11 toxic nodular goiters, 4 toxic adenomas, 3 amiodarone-induced thyrotoxicosis) between 2012 and 2014. All patients started MMI at 10 to 60 mg/day that was gradually tapered. We measured thyroid-stimulating hormone, free thyroxine, alanine aminotransferase (ALT) and aspartate aminotrasnferase (AST) at baseline and at 6 weeks, 4.5 months and 10 months after starting the MMI treatment. The concomitant medication was stable during MMI treatment. At baseline, 25 patients (32.5%) had abnormal LFT, of which 5 had ALT or AST levels >2× the upper limit of normal (ULN). In most patients with baseline abnormal LFT, MMI treatment resulted in a normalization of serum ALT and AST. Thirteen patients with normal baseline LFT had <2× the ULN elevations of LFT sometime during treatment. There was a case of significant hepatotoxicity. During treatment, there were no significant differences in LFT levels between patients with initially normal or abnormal LFT. In a Cox proportional hazard regression model, abnormal LFT at baseline, abnormal thyroid function at the last evaluation, and MMI dose were not predictors of abnormal LFT at the final evaluation. MMI treatment can induce insignificant LFT elevation, <2× the ULN. MMI can be safely administered in hyperthyroid patients with abnormal LFT, and normalization of increased AST and ALT levels should be anticipated. ALT = alanine aminotransferase AST = aspartate aminotransferase fT4 = free thyroxine HCV = hepatitis C virus LFT = liver function test LOCF = last observation carried forward MMI = methimazole PTU = propylthiouracil TSH = thyroid-stimulating hormone ULN = upper limit of normal.