Polymer-drug interactions and wetting of solid dispersions

Area of Science:

• Pharmaceutical Sciences
• Materials Science
• Physical Chemistry

Background:

• Solid dispersion technology is crucial for enhancing drug solubility and bioavailability.
• Tablet wetting is a critical factor influencing drug dissolution and absorption.
• Interactions between drugs and polymers in solid dispersions can affect physicochemical properties.

Purpose of the Study:

• To investigate the influence of model drugs on the wetting behavior of solid dispersion tablets.
• To explore the role of polymer type (HPMC vs. PVP) in drug-polymer interactions and surface properties.
• To elucidate the mechanisms behind unexpected changes in tablet surface hydrophobicity.

Main Methods:

• Preparation of solid dispersions using five model drugs with varying solubility and polymer interaction capabilities.
• Incorporation of drugs into hydrophilic polymer matrices: hydroxypropyl methylcellulose (HPMC) and polyvinyl pyrrolidone (PVP).
• Measurement of surface hydrophobicity using equilibrium advancing water contact angle.
• Utilized Nuclear Magnetic Resonance (NMR) imaging to track water ingress and swelling dynamics.

Main Results:

• Physical mixtures of drugs and polymers exhibited expected surface hydrophobicities.
• Solid dispersions containing HPMC showed significantly lower contact angles than pure components, indicating reduced hydrophobicity.
• NMR imaging provided insights into water uptake and swelling patterns within the solid dispersions.

Conclusions:

• Drug incorporation can unexpectedly alter the wetting properties of solid dispersion tablets.
• The observed decrease in hydrophobicity in HPMC-based dispersions is attributed to changes in intermolecular hydrogen bonding, leading to altered surface exposure of HPMC side groups.
• These findings highlight the complex interplay between drug properties, polymer characteristics, and solid dispersion formulation on critical performance attributes like wetting and dissolution.