Topic overview

Start with the big picture

Formulation begins with the API’s solubility and partitioning in the base, which influence drug release, skin penetration, and physical stability. Base selection—oleaginous, absorption, emulsion, or water-soluble—should reflect the drug’s polarity and the intended occlusive effect. Suspended drugs require suitable particle size for uniformity and acceptable texture. Viscosity and rheology affect spreading and dose retention, while control of pH, water activity, and preservation supports product quality. Additional considerations include permeation enhancement, excipient compatibility, oxidation, packaging interactions, and prevention of phase separation. Development also evaluates drug release, microbial limits, and stability, linking formulation choices to critical quality attributes.