Classification of Excipients for Transdermal Drug Delivery System

Transdermal drug delivery system is a type of drug formulation that is absorbed into the body circulation through capillaries at a certain rate through the skin to produce drug effects. Transdermal drug delivery systems allow the drug to continuously diffuse through the skin, penetrate and absorb into the blood circulation, maintain stable blood concentrations for a long time, reduce the frequency of drug administration, reduce individual differences in absorption and metabolism, and make transdermal drug delivery easy to apply and simple and rapid to stop drug administration in case of problems. Transdermal drug delivery formulations include creams, applicators, skeleton-type patches, membrane-controlled patches, microemulsions, liposomes, etc., which can produce local or systemic effects.

Classification of Excipients for Transdermal Drug Delivery System
There are six major categories of excipients used in transdermal drug delivery systems: membrane materials and skeletal materials, pressure-sensitive adhesives, backing materials, anti-adhesive materials, drug reservoir materials, and transdermal enhancers.

Membrane and skeleton materials
After the drug for transdermal drug delivery is determined, the selection of polymeric materials (membrane control materials and skeleton materials) is the main task in the development of transdermal drug delivery systems.

Pressure-sensitive adhesives
Pressure-sensitive adhesive refers to those adhesive materials that can be adhered under slight pressure and can be easily peeled off.

Backing material
The backing material is a film used to support the drug library or pressure-sensitive adhesive, etc. It is generally required to have good barrier performance against drugs, gum, solvents, moisture and light when the thickness is very small, and has good flexibility and certain tensile strength.

Anti-adhesive materials
These materials are mainly used for the protection of the adhesive layer of TDD system. In order to prevent the transfer of pressure-sensitive adhesive from the drug library or controlled-release film to the anti-adhesive material, the surface free energy of the selected material should be lower than the surface free energy of pressure-sensitive adhesive, and the affinity with pressure-sensitive adhesive is less than the affinity between pressure-sensitive adhesive and controlled-release film.

Drug reservoir materials
There are many drug reservoir materials that can be used, either a single material or a paste, ointment, hydrogel, suspension, solution, etc. configured with multiple materials.

Transdermal enhancers
Transdermal enhancers are all substances that can increase the speed of drug transdermal or increase the amount of drug transdermal.