Tablet levothyroxine (L-T4) malabsorption induced by proton pump inhibitor; a problem that was solved by switching to L-T4 in soft gel capsule.

OBJECTIVE: To report a patient in whom the impaired absorption of tablet levothyroxine (L-T4) due to a proton pump inhibitor (PPI) use was corrected by switching the patient to the soft gel capsule. METHODS: A woman with Hashimoto's thyroiditis-associated hypothyroidism (serum thyroid-stimulating hormone [TSH] 6.8-9.6 mU/L) had been treated with tablet L-T4 (100 μg/day). Because she used to take pantoprazole just before L-T4 in the morning, TSH failed to normalize (4.4-6.5 mU/L). Thus, the daily dose had been progressively increased to 125 and 150 μg/day, with serum TSH levels of 2.4 and 0.6 mU/L, respectively. RESULTS: While maintaining pantoprazole, we switched the tablet L-T4 (150 g/day) to a soft gel capsule (125 μg/day; Tirosint® capsule, IBSA, Lugano, Switzerland) and after 2 months, to 100 μg/day. Serum TSH was lower than under the equivalent regimens with the tablet: 0.5 versus 2.4 mU/L (125 μg/day) and 2.4 versus 4.4 to 6.5 mU/L (100 μg/day). Upon switching back to the tablet (100 μg/day), serum TSH increased to 3.2 and 4.7 mU/L and then dropped to 2.7-3.0 mU/L when the dose was increased to 125 μg/day. We also acutely evaluated the intestinal absorption of L-T4 by administering 600 μg LT4 as a tablet or soft gel capsule while maintaining pantoprazole. Pharmacokinetic indices showed better and faster absorption for the soft gel capsule versus tablet (area under the curve [AUC]0-4h = 16,240 vs. 10,960 nmol/L x 4 hours, maximum absorption [Cmax] = 108 vs. 73 nmol/L, and time of maximum absorption [Tmax] = 120 minutes vs. 180 minutes). CONCLUSION: Confirming in vitro studies conducted by other authors, the soft gel capsule L-T4 is negligibly affected by changes in gastric pH compared to tablet L-T4.