Physical and chemical stability of methotrexate,cytarabine,and hydrocortisone in Elliott’s B Solution for intrathecal use

Intrathecal administration of methotrexate sodium and cytarabine with or without hydrocortisone sodium succinate is commonly used to treat metastatic spread of malignancies to the leptomeninges. The existing stability information on these drug combinations is inadequate due to the clinical use of increased doses of the drugs, as well as a change in the formulation of Elliott’s B Solution. The purpose of this study was to evaluate the physical and chemical stability of simulated high intrathecal doses of the subject drugs in the current formulation of Elliott’s B Solution.

Methotrexate sodium 6, 12, and 15 mg was combined with cytarabine 100 mg with and without hydrocortisone sodium succinate 100 mg using Elliott’s B Solution as the intrathecal vehicle. Samples were stored at 4 and 23°C and evaluated for physical and chemical stability over 48 h.

No precipitation or other evidence of physical instability was observed in any sample. Measured pH was 7.2- 7.5 in the samples and was sufficient to prevent methotrexate precipitation. High-performance liquid chromatography analysis found little or no loss of methotrexate and cytarabine in any sample and hydrocortisone at 4°C. At room temperature, hydrocortisone losses of 6-8% occurred in 48 h.

The high doses of methotrexate sodium and cytarabine with or without hydrocortisone sodium succinate evaluated in this study are physically and chemically stable for 48 h at 4 and 23°C in Elliott’s B Solution.