Generic and brand-name L-thyroxine are not bioequivalent for children with severe congenital hypothyroidism

Abstract

Context: In the United States, generic substitution of levothyroxine (L-T4) by pharmacists is permitted if the formulations are deemed to be bioequivalent by the Federal Drug Administration, but there is widespread concern that the pharmacokinetic standard used is too insensitive. Objective: We aimed to evaluate the bioequivalence of a brand-name L-T4 (Synthroid) and an AB-rated generic formulation (Sandoz, Princeton, NJ) in children with severe hypothyroidism. Design: This was a prospective randomized crossover study in which patients received 8 weeks of one L-T4 formulation followed by 8 weeks of the other. Setting: The setting was an academic medical center. Patients: Of 31 children with an initial serum TSH concentration >100 mU/L, 20 had congenital hypothyroidism (CH), and 11 had autoimmune thyroiditis. Main Outcome Measures: The primary endpoint was the serum TSH concentration. Secondary endpoints were the free T4 and total T3 concentrations. Results: The serum TSH concentration was significantly lower after 8 weeks of Synthroid than after generic drug (P <3 yr of age. Our results may have important implications for other severely hypothyroid patients in whom precise titration of L-T4 is necessary. Copyright © 2013 by The Endocrine Society.