Liquid Levothyroxine May Prevent Malabsorption From Proton-Pump Inhibitors

the Endocrinology Advisor take:

Switching from levothyroxine tablets to an oral solution corrects impaired absorption caused by proton-pump inhibitors, according to a new study published in the Journal of Clinical Endocrinology & Metabolism.

Levothyroxine (LT₄) is one of the most prescribed drugs worldwide and is most commonly administered as a tablet. An acid gastric pH is needed to dissolve the LT4 so that it can be absorbed in the intestine. Commonly-prescribed proton-pump inhibitors (PPIs), however, increase gastric pH, which interferes with LT₄ dissolution.

LT₄ has recently been released in the form of an oral solution, which is absorbed faster than the tablet because no dissolution is necessary. Researchers wanted to test whether this formulation was resistant to interference from PPI.

The study included 24 patients whose tablet LT₄ absorption was impaired due to concomitant ingestion of PPI. To gauge LT₄ absorption, researchers measured thyroid-stimulating hormone (TSH) values at baseline (before switching to liquid LT₄), 8 weeks after the formulation change and again after another 8 weeks.

After switching, overall serum TSH levels were significantly lower post-switch compared with pre-switch levels. In 7.1% of the patients, LT₄ absorption increased so much that their doses had to be lowered to prevent hyperthyroidism.

These results demonstrate that liquid LT₄ absorption is unaffected by an increase in gastric pH due to PPI therapy, though additional studies are needed to verify whether liquid LT₄ is also resistant to other drugs known to impair LT₄ absorption.