API-polymer interactions in Sepineo P600 based topical gel formulation- impact on rheology

Area of Science:

• Pharmaceutical Sciences
• Materials Science

Background:

• Topical formulations require specific rheological properties for efficacy and stability.
• Acrylamide/ Sodium Acryloyldimethyl taurate copolymer (Sepineo P600) is a versatile gelling agent for semi-solid dosage forms.

Purpose of the Study:

• To evaluate the rheological attributes and physical stability of topical gel and emulsion gel formulations containing an Active Pharmaceutical Ingredient (API).
• To investigate the influence of pH and API concentration on the rheology of Sepineo P600-based formulations.

Main Methods:

• Formulation of topical gels and emulsion gels using Sepineo P600 as gelling agent.
• Incorporation of Lidocaine as a model API and Medium-chain Triglycerides (MCT) as the dispersed phase.
• Assessment of rheological properties (viscosity, elastic moduli, yield stress) and physical stability.

Main Results:

• Rheological properties were significantly influenced by formulation pH and API concentration.
• Lower pH (below API's pKa) weakened the gel matrix structure due to increased cationic lidocaine species.
• Electrostatic interactions between API and polymer chains altered rheology and potentially impacted emulsion gel stability.

Conclusions:

• The rheology of Sepineo P600 gels and emulgels can be tuned by manipulating API properties and formulation parameters like pH.
• These tunable properties and a straightforward manufacturing process make Sepineo P600 systems suitable for semi-solid topical applications.