semisolids

Semisolids are dosage forms with a physical state between solid and liquid, designed for local or mucosal delivery. They include ointments, creams, gels, pastes, and waxy bases, and are intended to release active ingredients at the site of application while providing a physical barrier or prolonged contact. The vehicle nature determines occlusivity, hydration of the skin, and drug release.

Ointments are typically lipid-based, oily or hydrocarbon vehicles that are occlusive and water-repellent; creams are emulsions (oil-in-water or water-in-oil) with varying lubricity; gels are networks of polymers with water or other solvents; pastes are thick suspensions with high solid content and a stiffer texture. Semisolids commonly exhibit non-Newtonian, shear-thinning behavior (thixotropy), affecting spreadability.

They are widely used in dermatology, wound care, and cosmetics for local action, barrier protection, hydration, or soothing effects. Advantages include easy topical administration, targeted delivery, and potential for sustained release; disadvantages can include greasiness, residue, limited water resistance, and storage sensitivity.

Manufacturing involves selecting a base, incorporating drug with appropriate technique (melt, fusion, or emulsification), controlling rheology, and ensuring stability. Quality evaluation covers viscosity and rheology, spreadability, adhesion, drug content uniformity, pH, odor and appearance, and microbial limits.