Prevalence of gastrointestinal disorders having an impact on tablet levothyroxine absorption: should this formulation still be considered as the first-line therapy?

Purpose: In patients with hypothyroidism, levothyroxine (LT4) is the treatment of choice, and tablets are the most commonly prescribed formulation. Despite multiple scenarios being reported in the literature with impaired tablet absorption and likely missed TSH targets, it is yet unclear what the implications are for clinical practice and the role of liquid solution (LS) and soft gel (SG) formulations. We have thus conducted a narrative review evaluating the prevalence within the general population of gastrointestinal disorders impacting tablet LT4 absorption. Methods: PubMed and Google Scholar were searched until December 2019 for systematic reviews and meta-analyses on the topic. If they could not be retrieved, other types of manuscripts were searched. Results: Lactose malabsorption and Helicobacter pylori infection represented the most common disorders, with a global prevalence of 68% and 48%, respectively. The prevalence of other conditions, including autoimmune gastritis, bariatric surgery, celiac disease, gastroparesis, giardiasis, liver cirrhosis, or ulcerative colitis, was lower than 20%. Data at regional and country levels were found to be heterogeneous, but at least one in five patients was diagnosed with one disorder. Conclusions: The worldwide prevalence of gastrointestinal disorders associated with tablet LT4 malabsorption, including lactose malabsorption and Helicobacter pylori infection, is high. Interactions with drugs or food can further increase this risk. Considering that all studies investigating the impact of switching patients from tablet to LS or SG found an improved thyroid balance, the latter formulations should be considered as first-line therapy for managing hypothyroidism.