Semi-solid formulations are pharmaceutical preparations that exhibit a consistency between a liquid and a solid, such as creams, ointments, gels, lotions, and pastes. These formulations require excipients to achieve the desired rheological properties, drug release and stability.
The excipients used in semi-solid formulations include:
1. Emulsifiers: Emulsifiers are used to stabilize emulsions, enhance the homogeneity of the formulation, and prevent separation of the dispersed phase from the continuous phase. Commonly used emulsifiers include nonionic surfactants such as polysorbate 80 and sorbitan monostearate.
2. Thickening agents: Thickening agents are used to increase the viscosity of the formulation, improve the stability of the formulation, and enhance adherence to the skin. Commonly used thickening agents include cellulose derivatives such as hydroxyethylcellulose and carbomers.
3. Solvents: Solvents are used to dissolve or disperse hydrophobic drugs and excipients. Commonly used solvents include propylene glycol and ethanol.
4. Humectants: Humectants are used to increase the water content of the formulation and retain it on the skin. Commonly used humectants include glycerol and urea.
5. Preservatives: Preservatives are used to prevent microbial growth in the formulation and extend the shelf life of the product. Commonly used preservatives include parabens and benzalkonium chloride.
6. Antioxidants: Antioxidants are used to prevent oxidation of the formulation, which can lead to degradation of the drug and decrease in efficacy. Commonly used antioxidants include ascorbic acid and tocopherol.
Overall, these excipients play a crucial role in the formulation of semi-solid products and can significantly impact the efficacy, stability, and safety of the final product.