Oral or Enteral Levothyroxine for Myxedema Coma When Intravenous Therapy Is Unavailable: A Systematic Review and Descriptive Evidence Synthesis.

OBJECTIVES

Intravenous levothyroxine is generally preferred for myxedema coma but may be unavailable in many healthcare settings. We summarized published treatment regimens and outcomes with oral or enteral levothyroxine when intravenous therapy was unavailable. Intravenous-only and mixed-route reports were included for clinical context.

METHODS

PubMed/MEDLINE, Embase, Scopus, and Web of Science were searched from inception through March 2026. Studies reporting myxedema coma treated with oral, enteral, nasogastric, or intravenous levothyroxine and extractable clinical outcomes were included. Pooled proportions were calculated only as descriptive summaries of oral/enteral reports and were not interpreted as treatment-effect estimates. Intravenous-only and mixed-route studies were summarized narratively. Methodological quality was assessed using Joanna Briggs Institute tools, and certainty of evidence using GRADE.

RESULTS

Nine studies comprising 70 patients were included: six oral/enteral, two intravenous-only, and one mixed-route study. Oral/enteral loading doses ranged from 300 to 1000 μg. Descriptively pooled proportions were 0.20 for mortality, 0.76 for intensive care unit admission, 0.54 for mechanical ventilation, and 0.62 for vasopressor requirement. These estimates are descriptive summaries of selected published reports and should not be interpreted as population-level event rates, treatment-effect estimates, route-specific risks, or expected outcome probabilities in routine clinical practice.

CONCLUSIONS

Published reports document oral or enteral levothyroxine as a rescue approach when intravenous treatment is unavailable. However, evidence is insufficient to establish comparative efficacy, safety, equivalence, or an optimal dosing regimen. Intravenous levothyroxine should remain preferred when available, particularly in patients with shock, ileus, or unreliable gastrointestinal absorption.