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Effect of ionic strength on solution stability of PNU-67590A, a micellar prodrug of methylprednisolone
1Pharmacia & Upjohn, Tsukuba Research Laboratories, Ibaraki, Japan. hirokazu.okamoto@am.pnu.com
Purpose:
PNU-67590A is a water-soluble micellar prodrug of methylprednisolone (MP). The major products of degradation of PNU-67590A are MP by hydrolysis and methylprednisolone 17-suleptanate (17-E) by 21-->17 acyl migration. The effect of ionic strength on micelle formation and stability of PNU-67590A in aqueous solution was examined.
Methods:
PNU-67590A solutions at pH 2 and 8 and ionic strength of 0.05, 0.1, 0.2, and 0.4 M were maintained at 25 degrees C in the dark to measure MP and 17-E levels over time.
Results:
The rate of degradation of micellar PNU-67590A at pH 8 was less than that of monomeric PNU-67590A, and vice versa at pH 2. Increase in ionic strength decreased both the critical micelle concentration of PNU-67590A and the degradation of micelle PNU-67590A at both pHs, resulting in improved overall stability of PNU-67590A.
Conclusions:
Formulation of PNU-67590A in a concentrated solution with high ionic strength will maximize stability and shelf-life.
Insights
High ionic strength enhances the stability and shelf-life of PNU-67590A, a methylprednisolone prodrug, by reducing its degradation in aqueous solutions.
Area of Science:
- Pharmaceutical Sciences
- Physical Chemistry
Background:
- PNU-67590A is a water-soluble micellar prodrug of methylprednisolone (MP).
- Key degradation products include MP (via hydrolysis) and methylprednisolone 17-suleptanate (17-E) (via acyl migration).
Purpose of the Study:
- To investigate the impact of ionic strength on micelle formation and PNU-67590A stability in aqueous solutions.
- To understand the degradation pathways of PNU-67590A under varying ionic conditions.
Main Methods:
- PNU-67590A solutions were prepared at pH 2 and 8 with ionic strengths of 0.05, 0.1, 0.2, and 0.4 M.
- Solutions were incubated at 25°C in the dark to monitor MP and 17-E levels over time.
Main Results:
- Degradation rates differed between micellar and monomeric PNU-67590A depending on pH.
- Increased ionic strength reduced the critical micelle concentration and degradation of PNU-67590A at both pH levels.
- Overall PNU-67590A stability was improved with higher ionic strength.
Conclusions:
- Formulating PNU-67590A in concentrated, high-ionic-strength solutions is recommended.
- This formulation strategy will maximize the stability and shelf-life of the methylprednisolone prodrug.