Intravenous Thyroxine Administration to Hospitalized Patients Outside of Approved Indications: A Common, yet Unreported Practice a Single-center Observational Study

Background:
Intravenous thyroxine (IVT4) is FDA-approved solely for the treatment of myxedema coma (MC). However, it appears IVT4 is not uncommonly administered for unapproved indications. We aimed to characterize a recent cohort of hypothyroid (HT) inpatients who received IVT4, to understand the motives behind treatment, and to assess their outcomes.

Methods:
A retrospective study of all admissions at Tel Aviv-Sourasky Medical Center between 01.01.2017-30.06.2020, during which at least one dose of IVT4 was administered. Demographic, clinical data, and outcomes were retrieved. A MC index (MCI), together with the age-adjusted Charlson co-morbidity index (AACCI), were used to assess the patients’ clinical condition. A multivariate analysis was performed to explain the outcome death.

Results:
IVT4 was administered to 104 HT subjects over the course of 110 admissions. MC was confirmed in only 4 (3.6%), 11 subjects received IVT4 for lack of enteral access/malabsorption. Thus, IVT4 was administered for ATA-endorsed indications in only 15/110 (13.6%) of the cases. The most common justification for treatment was perceived profound hypothyroidism (57/110, 51.8%). There were 27 fatalities (24.5%). In a logistic regression, artificial ventilation (aOR 7.69 [CI 2.3-28.3], P=0.0012), and the AACCI (aOR 1.34 [CI1.09-1.73], P=0.012 were the only significant independent predictors of death. Thyroid function tests had no discriminatory power.

Conclusions:
IVT4 was rarely given for ATA-endorsed indications. Although it doesn’t appear to be detrimental, a beneficial effect on outcome remains unproven. Death was due the patients’ condition, not to hypothyroidism. Controlled prospective trials of IVT4 for indications other than those currently ATA-approved are required.