January - March 2025, Volume 21, Issue 1

Cetin K, Donbaloglu Z, Singin B, Bahar YF, Ozdem S, Parlak M, Tuhan H

Levothyroxine-Simethicone Drug Interaction and Presence of Macro-TSH in an Infant with Congenital Hypothyroidism

Acta Endo (Buc) 2025, 21 (1): 127-130
doi: 10.4183/aeb.2025.127

Introduction. Congenital hypothyroidism (CH) is a prevalent cause of intellectual disability, preventable with early detection and treatment. Levothyroxine (LT4) is the standard treatment, but its efficacy can be compromised by drug interactions. Case Description. We present an 18-day-old boy diagnosed with CH, who exhibited elevated thyroidstimulating hormone (TSH) levels despite LT4 treatment. Upon increasing the LT4 dose and observing persistent TSH elevation, further investigation revealed the concurrent use of simethicone-containing colic drops. Literature suggests that simethicone can interfere with LT4 absorption. The colic drops were discontinued, leading to normalized TSH levels. Additionally, macro-TSH, indicated by a polyethylene glycol (PEG) precipitation test, was considered to contribute to the elevated TSH levels. Discussion. This case underscores the necessity of thorough medication history reviews in patients with CH. Drug interactions, such as those with simethicone, can significantly impact LT4 efficacy. Moreover, the presence of macro-TSH should be considered when TSH levels are disproportionately elevated. Conclusion. Clinicians should be vigilant about over-the-counter medication use and potential interactions in managing CH. Comprehensive patient history and careful monitoring are critical to optimizing treatment outcomes.

Keywords: congenital hypothyroidism, drug interaction, levothyroxine, simeticone.

Correspondence: Hale Tuhan, MD, Akdeniz University, Faculty of Medicine Hospital, Department of Pediatric Endocrinology, Pinarbasi 07070, Antalya, Turkey, E-mail: halenvr@hotmail.com