Hildebrand solubility parameter to predict drug release from hydroxypropyl methylcellulose gels

Area of Science:

• Pharmaceutical Sciences
• Materials Science
• Physical Chemistry

Background:

• Drug release from polymer matrices like hydroxypropyl methylcellulose (HPMC) is crucial for controlled drug delivery.
• Understanding the factors influencing drug release kinetics is essential for optimizing dosage forms.

Purpose of the Study:

• To develop and validate a predictive model for drug release from HPMC gels.
• To investigate the relationship between drug properties, particularly Hildebrand solubility parameter, and release kinetics.
• To evaluate the applicability of established drug release models, such as the Peppas equation, across a range of drugs.

Main Methods:

• Development of a novel equation incorporating the Hildebrand solubility parameter (δ) to model drug release.
• Experimental determination of release data for six model drugs (caffeine, theophylline, paracetamol, salicylic acid, naproxen, diclofenac) with varying polarity.
• Analysis of release data using the developed equation and the Peppas exponential law (M/M(∞) = Kt(n)).
• Statistical validation of the models using coefficient of determination (r²).

Main Results:

• The proposed equation accurately models drug release (r² = 0.94) and incorporates drug solubility parameter (δ) and initial concentration (C(i)).
• Drug release is generally linear in the initial 5-6 hours, with zero-order constants (K(o)) increasing with higher drug solubility parameters.
• The Peppas law is applicable to significant fractional releases, with its applicability duration varying based on drug polarity (lower δ for less polar drugs, higher δ for more polar drugs).
• The diffusional exponent (n) values (0.40-0.58) indicate diffusion-controlled drug release.
• An extended Peppas equation incorporating initial concentrations also showed good correlation (r² = 0.88-0.94).

Conclusions:

• The Hildebrand solubility parameter is a valuable parameter for modeling and predicting drug release from HPMC gels.
• The developed model provides a robust framework for understanding drug release behavior based on drug physicochemical properties.
• Diffusion is the primary mechanism controlling drug release in these HPMC gel systems.