Degradation kinetics of neostigmine in solution

Area of Science:

• Pharmaceutical Chemistry
• Physical Chemistry
• Drug Stability Studies

Background:

• Neostigmine is a crucial pharmaceutical agent.
• Understanding its degradation kinetics is vital for formulation development and shelf-life determination.
• Accelerated storage conditions are employed to predict long-term stability.

Purpose of the Study:

• To elucidate the degradation kinetics of neostigmine in aqueous solutions across a wide pH range (1.5–9.9).
• To investigate the impact of different solvents (propylene glycol, polyethylene glycol 400) on neostigmine stability.
• To determine optimal conditions for neostigmine stability, including pH and the absence of UV light.

Main Methods:

• Kinetic analysis of neostigmine degradation in aqueous buffers.
• Assessment of neostigmine stability in solutions containing propylene glycol and polyethylene glycol 400.
• Evaluation of degradation under UV irradiation (254 nm) versus light-protected conditions.
• Determination of activation energy using Arrhenius plots.

Main Results:

• Neostigmine degradation followed pseudo-first-order kinetics in aqueous and solvent systems.
• Degradation rate was independent of buffer species but influenced by pH, with maximum stability at pH 5.0.
• Estimated half-life at room temperature was 883.7 days in pH 4.9 acetate buffer.
• UV irradiation accelerated degradation; propylene glycol enhanced stability, whereas polyethylene glycol 400 reduced it.

Conclusions:

• Neostigmine exhibits pseudo-first-order degradation kinetics, with pH 5.0 being optimal for stability.
• Formulation strategies involving propylene glycol can improve neostigmine stability, while polyethylene glycol 400 should be avoided.
• Protection from UV light is recommended to maintain neostigmine integrity over time.