A generalized relation for solid-state drug stability as a function of excipient dilution: temperature-independent...

Area of Science:

• Pharmaceutical Sciences
• Physical Chemistry
• Materials Science

Background:

• Solid-state chemical stability is crucial for drug product shelf-life.
• Excipients significantly influence drug degradation kinetics.
• Understanding excipient-drug interactions is key to formulation development.

Purpose of the Study:

• To propose and validate a generalized relationship for excipient impact on drug product solid-state chemical stability.
• To investigate the influence of drug and excipient particle ratios on degradation rates.
• To establish a predictive model for degradant formation under varying conditions.

Main Methods:

• Development of a generalized mathematical model for excipient effects on drug degradation.
• Experimental validation using two model drug products and multiple degradation pathways.
• Analysis of degradant formation rates across different drug concentrations, temperatures, and relative humidities.

Main Results:

• A generalized relationship was established, consistent across multiple degradation products and drugs.
• When drug particles are in excess, a power-law relationship (slope ~2/3) was observed, supporting a "quasi-liquid" model.
• The observed power-law slopes were independent of temperature, suggesting a robust kinetic relationship.

Conclusions:

• The proposed generalized relationship accurately describes excipient influence on drug stability.
• The "quasi-liquid" model provides a mechanistic basis for observed degradation kinetics.
• This model offers a valuable tool for predicting and optimizing drug product stability during formulation.