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Anaerobic stability of aqueous physostigmine solution
J L Chen1, M K Yeh, C H Chiang
1School of Pharmacy, National Defense Medical Center, Taipei, Taiwan.
Drug Development and Industrial Pharmacy
|July 29, 2000
Summary
Physostigmine stability was assessed under anaerobic conditions. Optimal stability was observed at pH 3.4, suggesting a shelf life of 4 years, crucial for pharmaceutical formulation.
Area of Science:
- Pharmaceutical Chemistry
- Analytical Chemistry
Background:
- Physostigmine is a vital pharmaceutical agent.
- Understanding its degradation pathways is critical for drug stability and efficacy.
- Previous studies have not fully elucidated its anaerobic stability.
Purpose of the Study:
- To investigate the anaerobic stability of physostigmine.
- To determine the optimal pH and temperature conditions for physostigmine stability.
- To estimate the shelf life of physostigmine solutions under anaerobic conditions.
Main Methods:
- High-performance liquid chromatography (HPLC) with photodiode array and UV detection was used for identification and quantification.
- pH-rate profiles were evaluated at various temperatures (45°C, 55°C, 70°C) across a pH range of 2.4–6.8.
- Degradation kinetics and activation energies were calculated.
Main Results:
- The minimum degradation rate constant for physostigmine was observed at pH 3.4.
- Degradation was characterized as specific acid-base catalysis.
- Activation energies for anaerobic degradation were determined.
- Aerobic to anaerobic rate constant ratios ranged from 2-33 at 88°C, increasing with pH.
Conclusions:
- Physostigmine exhibits optimal stability under anaerobic conditions at pH 3.4.
- The estimated shelf life of physostigmine solution is 4 years at room temperature under these conditions.
- These findings are essential for developing stable pharmaceutical formulations of physostigmine.