Switching Levothyroxine From the Tablet to the Oral Solution Formulation Corrects the Impaired Absorption of Levothyroxine Induced by Proton-Pump Inhibitors

Context: Proton-pump inhibitors (PPIs) impair tablet levothyroxine (LT4) intestinal absorption by increasing the gastric pH and decreasing LT4 dissolution in the stomach. Objective: The purpose of this study was to verify whether a liquid formulation of LT4 would correct LT4 malabsorption induced by PPIs. Design: This was a prospective observational cohort study. The study was conducted from 2012 to 2013, and the mean duration of the follow-up was 23.7 ± 11.9 weeks. Setting: The study was conducted in a tertiary university hospital outpatients clinic. Patients: Upon informed consent, we recruited 24 consecutive adult patients (18 women and 6 men), who took LT4 for replacement (n = 14) or suppressive purposes (n = 10) and who had absorption of tablet LT4 impaired by PPIs. Intervention: The 24 patients were switched from the tablet to the oral solution LT4 at the same daily dose. Main Outcome Measures: Significantly lower mean TSH levels were seen with the oral solution than with the tablet as were significantly greater rates of serum TSH less than or equal to the specified cutoff values (replacement [REP] group) or ≤0.10 mU/L (suppressive [SUP] group) with the oral solution than with the tablet. Results: Serum TSH was lower with the oral solution than with the tablet formulation (REP group, 1.7 ± 1.0 mU/L vs 5.4 ± 4.3, P < .0001; SUP group, 0.1 ± 0.3 mU/L vs 2.1 ± 2.7, P < .0001). In the REP group, the rate of TSH values of ≤4.12 or ≤2.5 mU/L was 29 of 30 (96.7%) or 24 of 30 (80.0%) postswitch but only 17 of 36 (47.2%) or 9 of 36 (25.0%) preswitch (P < .0001). In the SUP group, the rate of serum TSH values of ≤0.10 mU/L was 26 of 35 (74.3%) postswitch but 0 of 22 (0%) preswitch (P < .0001). Conclusions: These data demonstrate the continued absorption of liquid LT4 despite the increased gastric pH due to PPI therapy.