Endocrine Abstracts

Recent reports have proven gastric pH as key for both dissolution and bioavailability of oral thyroxine. This is clinically relevant in patients with gastric disorders to tailor an individualized treatment. In vitro, the softgel preparation of thyroxine possess a superior dissolution profile at increasing pH than the tablet T4. No data are available analyzing the correlation between the gastric pH and the softgel T4 performance in vivo and the present study is aimed at investigating this topic. Twenty height hypothyroid patients (24F/4M; median age=48 years) in need for endoscopy were enrolled. These patients were treated since at least 2 years with a stable dose of tablet T4 (median dose=1.65 μg/kg per day) and pledged to take thyroxine in fasting conditions, then abstaining from eating or drinking for at least one hour. The compliance with LT4 treatment has been checked by interviewing patients and confirmed by stable TSH values (<0.8–2.5 mU/l). All these patients underwent endoscopy for either dyspepsia or follow up of gastric disorders. Gastric juice has been sampled during endoscopy to measure H+ concentrations in gastric juice. Then they have been shifted to softgel LT4 at a minimum effective dose, individually titrated to obtain a similar TSH concentration for at least six months. In the whole sample, the median concentration of H+ in the gastric juice was 52 mEq/l. Based on this value, patients were subdivided in two groups: Group A (n=16) with a normal median H+ concentrations of 77 mEq/l (median pH=1.5) and Group B (n=12) showing a very low median H+ concentrations of 13 mEq/l (median pH=4.3). The concentration of H+ correlated with the dose of LT4 in both groups although to a different extent(tablet: r=0.5810 P<0.0001 and softgel: r=0.2079; P=0.0147). In the group A (normal gastric acid), following the switch tablet/softgel, no patients showed a lower T4 requirement. In contrast, in the group B (very low acidity) 10/12 (83%, P<0.0001; RR=6; PPV 100%) required a reduced dose of softgel T4. The median dose in these latter patients was reduced from 1.92 to 1.67 μg/kg per day (−15%).The findings of this in vivo evaluation revealed that the dose of both tablet and softgel thyroxine correlates with gastric acidity but softgel T4 formulation should be the preferred one in hypothyroid patients with impaired gastric acid secretion.