Stability of a standardized preparation of methotrexate, cytarabine, and methylprednisolone hemisuccinate for intrathecal use

Introduction: Data about the feasibility or stability of drugs prepared for intrathecal administration are scarce, especially concerning the possibility of mixing two or more compounds in the same syringe. We evaluated the stability of an extemporaneously prepared triple intrathecal therapy containing methotrexate, cytarabine, and methylprednisolone hemisuccinate.

Materials and methods: Six mixtures containing 12.5 mg methotrexate, 50 mg cytarabine, and 40 mg methylprednisolone hemisuccinate, diluted to a final volume of 5 ml with water for injection, were prepared in polypropylene syringes on six different days. Syringes were stored protected from light either at room temperature (20°C) (n = 3) or refrigerated temperature (4°C) (n = 3). Samples were analyzed immediately after preparation and again at 0.5, 2, 4, 6, 8, and 24 h. The analysis was conducted with a high-performance liquid chromatography instrument equipped with a quaternary pump and diode array detector. pH was also assessed before every sample analysis.

Results: When mixed in a polypropylene syringe, the three drugs were stable at both temperatures tested. No degradation >10% was observed in any sample and pH remained between 7.0 and 7.5 over time. No precipitation or color change occurred. Among the three compounds, methylprednisolone hemisuccinate was the most labile as a slight temperature- and time-dependent degradation was observed.

Conclusion: Triple intrathecal solution of methotrexate, cytarabine, and methylprednisolone hemisuccinate is stable for up to 24 h when stored in polypropylene syringes protected from light at 4°C and 20°C.