Feasibility of Reducing L-Thyroxine Dose in Patients with a Suppressed Serum Tsh

Abstract

A total of 748 patients on L-thyroxine with a suppressed serum TSH were requested to reduce their dose and this was achieved in 601 patients. Thyroxine dosage was reduced by 25 or 50μg of L-thyroxine and patients were reviewed six months later. Of all 601 patients, 54.4% remained with a suppressed serum TSH despite dose reduction and in 5.8% an elevated serum TSH resulted. 25μg reductions and 50μg reductions were equally likely to result in an detectable but non-elevated serum TSH (42.8% vs 34.1% ns) but 25μg reductions were less likely to result in an elevated serum TSH (3.8% vs 10.0% p<0.01). Only 7/601 patients in the study (1.2%) appeared to require a dose of over 150μg. If dose reduction is thought to be necessary for patients with a suppressed serum TSH, we would recommend 50μg reductions if the original dose is 200μg or more, and 25μg reductions if the original dose is 175μg or less.