there are indeed issues related to the stability of intravenous levothyroxine

J Perinat Med. 2011 Jul;39(4):471-5. doi: 10.1515/JPM.2011.051. Epub 2011 May 17.

Stability of thyroid hormones during continuous infusion.

Golombek SG1, Alpan G, Frey M, Corbi D, Lagamma EF.

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Abstract

We investigated the stability of thyroid hormones during a mode of continuous drug infusion via polypropylene tubing using the same conditions that would be applied to treating patients in a hospital setting. The diluted thyroid hormones were prepared using aseptic technique, stored at 2-8°C (36-46°F) and tested within 24 h of preparation for stability and percent recovery from within plastic tubing. Experiments were done in duplicate with triplicate sets of readings for each assay point. Only T(4) prepared with 5% dextrose water (D5W) containing 1 mg/mL albumin remained constant, stable, predictable and accurate over time under various conditions. Other methods of preparation lost drug by adhering to the plastic containers and tubing by as much as 40% of starting concentration. T(3) recovery in the presence of 1 mg/mL of albumin was 107±2% (mean±standard error of the mean) of anticipated drug concentrations. We conclude from this series of experiments that to maintain an accurate and stable dosing of patients receiving intravenous thyroid hormones, 1 mg/mL of albumin must be added to the infusate to prevent lost on the plastic intravenous tubing.

Prog Transplant. 2009 Dec;19(4):354-6; quiz 357.

Stability of levothyroxine sodium 0.4 microg/mL in 0.9% sodium chloride injection.

Stadalman KA1, Kelner MJ, Box K, Dominguez A, Rigby JF.

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Abstract

CONTEXT:

Intravenous levothyroxine therapy decreases vasopressor requirements and prevents cardiovascular collapse in hemodynamically unstable patients eligible for organ donation. The stability of levothyroxine when used in this manner is unknown.

OBJECTIVE:

To determine the stability of levothyroxine solution for intravenous use at a concentration of 0.4 microg/mL diluted in 0.9% sodium chloride.

DESIGN:

Triplicate sample sets were prepared by reconstituting levothyroxine 200 microg for injection with 5 mL of 0.9% sodium chloride with further dilution in 500 mL of 0.9% sodium chloride. One sample set was protected from light and the other was left unprotected. Both sample sets were stored at room temperature, and samples from each were analyzed for initial concentration and 4, 8, 12, and 24 hours later.

CONCLUSIONS:

Levothyroxine sodium 0.4 microg/mL in 500 mL 0.9% sodium chloride is stable for 24 hours at room temperature when protected from light.

Comment in

Proper analysis and interpretation of the stability of levothyroxine sodium 0.4 microg/mL in 0.9% sodium chloride injection. [Prog Transplant. 2010]

I don't know if this helps at all but recalled MHRA concerns about levothyroxine stability https://www.gov.uk/government/publications/levothyroxine-a-review-of-clinical-and-quality-considerations