Stability parameter estimation at ambient temperature from studies at elevated temperatures

Area of Science:

• Pharmaceutical Chemistry
• Chemical Kinetics
• Drug Stability

Background:

• Kinetic constants (k(i)) are crucial for drug stability but often determined at elevated temperatures.
• Existing methods for extrapolating to ambient temperatures have statistical limitations.
• Accurate kinetic data at storage temperatures are vital for drug formulation and storage decisions.

Purpose of the Study:

• To develop a nonlinear model for directly determining specific activation energies (E(ai)) linked to kinetic constants (k(i)).
• To establish a mathematical relationship between drug concentration, pH, temperature, and time.
• To provide statistically unbiased kinetic parameters at ambient temperatures from elevated temperature data.

Main Methods:

• A novel nonlinear model was developed.
• The model directly determines specific activation energies (E(ai)).
• Acetylsalicylic acid (ASA) hydrolysis data were used for model validation.

Main Results:

• The proposed model allows direct determination of kinetic parameters (k(i), E(ai), pK(a)) at low temperatures.
• An extrapolation procedure using the nonlinear model yields statistically improved results.
• The model successfully predicts kinetic parameters from data gathered at elevated temperatures.

Conclusions:

• The developed nonlinear model offers a statistically sound method for assessing drug stability at ambient temperatures.
• This approach enhances the reliability of kinetic data for drug formulation and storage.
• Direct determination of kinetic parameters at storage temperatures is achievable, improving practical decision-making.