Transdermal patches are a popular choice for drug delivery because of the sustained drug levels, low side effects, reduced hepatitic first-pass effect and ease of application, including self–administration. The basic components of any transdermal delivery system include the drug(s) dissolved or dispersed in a reservoir or inert polymer matrix; an outer backing film of paper, plastic, or foil; a pressure-sensitive adhesive that anchors the patch to the skin and a release liner, protecting the adhesive before application.
Drug release speed is determined by the complex relationships between the polymer matrix used, the layer thickness, membrane permeability, if any, and the content and concentration of drug. Some patches have an over saturated matrix to achieve a partial crystallization of the drug out of solution. The presence of both molecular solute and solid crystals in each patch allows for higher drug content and provides a longer lasting and consistent supply of drug.
After API is suspended in either a reservoir or inert polymer matrix, it is important to assess its physical form, drug particle size, and the formation of agglomerates. Gateway Analytical has developed a method using Raman Chemical Imaging to characterize multilayer polymer systems such as transdermal patches including the heterogeneity of the Active Pharmaceutical Ingredient (API) in reservoir transdermal patches.