Conclusion

Pasty or semi-solid systems for topical administration are highly complex, due to their particular rheological properties and the constraints of pharmaceutical application. These constraints are both technical and regulatory, and reference is always made to the European Pharmacopoeia in this sector.

Semi-solid products come in a wide variety of forms. Their solid consistency at rest is ensured by the continuous network formed by consistency agents: thickeners, gelling agents, particles in concentrated suspension. However, flow is possible by destructuring the network through the application of mechanical stress above the flow threshold. The term semi-solid describes this dual rheological property: solid at rest and fluid under flow. Active substance diffusion is nevertheless possible, as the semi-solid network macroscopically immobilizes a medium that remains liquid...