Endocrine Abstracts

Hypothyroid patients with gastric disorders require a higher dose of oral thyroxine (T4) to reach target serum TSH. In vitro evidence supports the notion that the variations of gastric pH may also interfere with T4 dissolution profile. The present study is aimed at confirming in vivo the supposed correlation between the gastric pH, directly measured during endoscopy, and the therapeutic dose of thyroxine using a controlled treatment schedule. A total of 61 tablet T4-treated hypothyroid patients (52 W/9M; median age=51 years; BMI=25.2) have pledged to take thyroxine in fasting conditions, abstaining from eating or drinking for one hour. Gastric juice for pH evaluation as well as multiple biopsy specimens were collected in all patients during endoscopy. The dose of T4 was calculated in each patient and compared to the one observed in age- and BMI-matched group of patients but positively devoid of gastrointestinal and/or pharmacological interference to measure the excess of T4 required. The results were plotted against the actual pH and the H⁺ concentration titrated with NaOH^- in each patient. All patients reached target serum TSH (median=1.29 mU/l) but the dose of oral thyroxine required increased along with the rising gastric pH (r²=0.1209; P< 0.0223) and the diminished H⁺ concentration (r²=0.1275; P<0.0219). A multivariate analysis revealed that pH act as an independent variable in determining the dose of T4 (P<0.029). Noticeably, even the excess of T4 dose (ED) required, plotted against gastric acidity in each patient, was highly correlated with the increased pH (P<0.001) and the decreased H⁺ concentrations (P<0.0001). Patients were then subdivided in two groups, using as cutoff the median value of their pH in the whole sample (2.4; IQ=1.5–6.1). Required T4 dose was slightly increased only in eight out of 34 patients (23%) in group A (median pH=1.52; median increase=15%). In group B (median pH=6.36), on the contrary, 25 patients out of 27 (93%; P<0.0001) needed a higher T4 dose and the median increase was huge (+47%). Increased T4 requirement was also unevenly distributed in patients with atrophic gastritis (90%), with pangastritis (73%) and with antritis (40%). The results of this in vivo study enlighted a highly significant correlation between gastric pH and the need for thyroxine in humans.