Enhancing the relative safety of intentional or unintentional intrathecal methylprednisolone administration by removing polyethylene glycol.

BACKGROUND

Previous studies have shown that intrathecal methylprednisolone is a very effective treatment for postherpetic neuralgia. However, widespread use of intrathecal methylprednisolone is limited by the presence of polyethylene glycol (PEG) as a preservative in the commercial formulation. In this study, we are proposing a method to reduce the concentration of PEG in the methylprednisolone acetate (MPA) suspension by inverting a vial before sterilely aspirating the contents into a syringe for subsequent injection. The purpose of this brief study was to precisely quantify the concentration of PEG in the MPA suspension.

METHODS

Single-dose vials containing 80 mg of MPA suspension were inverted to promote partition of the PEG away from the steroid component. After achieving 2 phases, we carefully extracted and aspirated only the steroid component. We kept the vials inverted for different time points (from 0 to 480 minutes), and we measured the concentration of PEG and methylprednisolone by using liquid chromatography and mass spectrometry. We also measured the pH of samples by using the pH meter for small samples.

RESULTS

The 1-way analysis of variance with post hoc analysis and Bonferroni correction showed statistically significant differences (P < 0.0001) between baseline concentrations and concentrations after inverting the vials for different times. We removed a minimum of 78% of PEG (the Bonferroni-corrected lower confidence limit for overall reduction in PEG) by keeping the vials inverted from 2 to 4 hours, and the average amount removed was 85% per vial. However, we did not change the concentration of methylprednisolone or the pH of the solution.

CONCLUSIONS

We believe that by decreasing the PEG concentration using our method, MPA-related complications will potentially be reduced, and this should be considered in patients with postherpetic neuralgia refractory to other treatments who might be candidates for repeated intrathecal injections.