Endocrine Abstracts

JOINT2364

Background: Oral Levothyroxine (LT4) is the primary treatment for hypothyroidism and requires an acidic gastric pH for absorption. On the other hand, Proton Pump Inhibitors (PPIs) are the most effective treatment for gastric acid suppression. Simultaneous use of LT4 and PPI can be challenging even for experienced physicians.

Case Presentation: A 70-year-old female with Hypothyroidism and Helicobacter pylori infection, who is compliant with her Levothyroxine and Pantoprazole, presented to the hospital with a 3-week onset of fatigue and chest pain. She denied lethargy, constipation, cold intolerance, weight gain, or any bleeding. Vital signs showed T 36.8C, HR 63bpm, and BP 110/60mmHg. Physical examination showed intact sensorium, no thyromegaly, edema, murmurs, or abnormal lung and abdominal findings. Diagnostic tests were remarkable for TSH 31.33 mIU/l(0.5-5 mIU/L), FT4 0.6 ng/dl (0.8-1.8 ng/dl), normal Troponin, EKG with low voltage QRS, chest X-ray showed cardiomegaly, echocardiogram showed new pericardial effusion without tamponade. The cardiology team suggested no urgent intervention. The endocrinology team increased her levothyroxine dose; the pharmacy was consulted for an LT4 liquid or gel formulation however, it was unavailable. Her Pantoprazole was switched to Famotidine which was administered 4 hours after LT4. Her symptoms improved, and she was discharged with strict follow-up for thyroid function testing and a repeat echocardiogram.

Discussion: PPIs suppress gastric acid for 48 hours due to their irreversible binding to H-K ATPase on parietal cells. Previous studies showed that using PPI in the morning or night while on LT4 causes an almost equal degree of TSH elevation. Alternatively, since Histamine 2 Receptor Blockers (H2RB) suppress acid secretion for only 4 hours, LT4 can be given 4 hours after H2RB administration. Increasing LT4 doses may be considered but can predispose patients to side effects. Interestingly, LT4 gel capsules and liquid formulations do not require acidic pH for absorption and are unaffected by PPI. Rectal and IV LT4 are options for acute needs but are tedious for maintenance administration.

Conclusion: Patients on LT4 requiring concurrent acid suppression can benefit from H2RB and Gel coated or liquid formulations of LT4. Patients should be re-educated regarding the need for strict outpatient follow-up with close monitoring of thyroid function tests.

Reference: Seng Yue C et al. Proton pump inhibitors do not affect the bioavailability of a novel liquid formulation of levothyroxine. Endocr Pract 2024;30(6):513-520; doi: 10.1016/j. eprac.2024.03.388. PMID: 38554774.