Generic Levothyroxine Compared With Synthroid in Young Children With Congenital Hypothyroidism

Context: Clinicians who prescribe levothyroxine (LT4) for hypothyroidism often feel strongly about using a brand-name drug instead of a generic. Objective: The objective of the study was to determine whether Synthroid resulted in better control of congenital hypothyroidism than generic LT4. Design: This was a 5-year retrospective study. Setting: The study was conducted at 1 tertiary care center. Patients: Children who were 0–36 months old with congenital hypothyroidism followed up at our center from 2006 to 2011 were treated with either Synthroid exclusively (35 subjects) or generic LT4 exclusively (27 subjects). Interventions: We recorded the subjects' TSH and free T4 measurements, how often their LT4 dose was adjusted, and the duration of follow-up. Main Outcome Measure: TSH variance between the groups was measured. Secondary end points were the frequency of LT4 dose changes and the variance in free T4. Results: Using the Wilcoxon rank sum test, there was no difference in TSH SD in the Synthroid group compared with the generic group (median 3.0 vs 2.2, P = .27). Using a linear mixed model, children treated with the generic LT4 had lower TSH estimated SD [1.35 with 95% confidence interval (CI) (1.194, 1.526)] than the Synthroid group [1.66 with 95% CI (1.536, 1.803)]. Similarly, no difference was observed in free T4 SD between the groups using the Wilcoxon rank sum test (median 0.29 generic vs 0.36 Synthroid, P = .11), but the generic group had lower free T4 estimated SD than the Synthroid group using the linear mixed model [0.216 with 95% CI (0.187, 0.249) vs 0.298 with 95% CI (0.273,0.326)]. Frequency of LT4 dosing adjustments was similar between the groups, both in total (median 2.0 for generic vs 3.0 for Synthroid, P = .097) and when adjusted for number of TSH checks (ratio 0.25 generic vs 0.31 Synthroid, P = .45). Conclusions: In our study of congenital hypothyroidism, generic LT4 treatment resulted in similar or better control of hypothyroidism compared with Synthroid, as assessed by the clinical outcomes of TSH variance and the frequency of LT4 dosing adjustments.