Description
Omeprazole raises gastric pH, which impairs the dissolution and absorption of levothyroxine, resulting in reduced thyroid hormone bioavailability and potential hypothyroid relapse.
Mechanism
Levothyroxine (T4) dissolves optimally at low gastric pH; proton-pump inhibitor-mediated achlorhydria slows dissolution, reducing the fraction absorbed in the proximal small intestine. Some studies suggest up to 37% reduction in levothyroxine absorption.
Clinical Significance
Multiple prospective studies demonstrate significantly elevated TSH levels in patients stable on levothyroxine after PPI initiation, particularly at higher PPI doses and in patients with atrophic gastritis.
Management
Administer levothyroxine 30–60 minutes before the PPI if possible, or consider liquid or soft-gel levothyroxine formulations (less pH-dependent absorption); recheck TSH 6–8 weeks after initiating or changing PPI therapy.