In-use stability of diluted thiamazole (methimazole) infusion solutions in prefilled 0.9% sodium chloride infusion bags for continuous infusion.

OBJECTIVE: In patients with severe hyperthyroidism unable to tolerate oral antithyroid therapy, diluted thiamazole infusion solutions (dose 120-240 mg) are administered by continuous infusion over 24 hours. Information about the type of diluent and compatibility/stability of the ready-to-administer thiamazole preparation is missing in the summary of product characteristics of the injection concentrate marketed in Germany. We studied the in-use stability of diluted infusion solutions over 24 hours.
METHODS: Thiamazol 40 mg inject. Henning was diluted in prefilled polyolefin infusion bags containing 250 mL 0.9% sodium chloride (NaCl) infusion solution and kept for 24 hours at room temperature and diffuse room light. Content of the diluted infusion solutions (0.48 and 0.96 mg/mL) was analysed every 4 hours over the course of 24 hours by reversed-phase high-performance liquid chromatography. pH was measured after 0, 12 and 24 hours. The infusion bags were regularly inspected for visible particles. Subvisible particles were measured by particle counting.
RESULTS: Thiamazole infusion solutions of the nominal concentrations 0.48 and 0.96 mg/mL in 0.9% NaCl diluent, kept at room temperature under diffuse room light, are physicochemically stable over a period of at least 24 hours. No evidence of colour change, particle formation or pH change was observed throughout the observation period.
CONCLUSION: Dilution of 120 or 240 mg doses of licensed thiamazole injection concentrate with 0.9% NaCl infusion solution in prefilled polyolefin containers is recommendable for continuous infusion over 24 hours in the treatment of thyrotoxicosis. © European Association of Hospital Pharmacists 2022. No commercial re-use. See rights and permissions. Published by BMJ.