druginadhesive

Drug-in-adhesive (DIA) refers to a formulation approach in transdermal drug delivery systems where the active pharmaceutical ingredient is dispersed within the pressure-sensitive adhesive that directly adheres to the skin. This design contrasts with reservoir or matrix systems that place the drug in a separate compartment or behind a rate-controlling layer.

Common adhesive chemistries for DIA include acrylate- and silicone-based pressure-sensitive adhesives. The drug is typically dissolved or dispersed as solid particulates within the adhesive matrix. Additional excipients such as plasticizers or permeation enhancers may be included to modify release rate and skin permeation. The patch’s backing and protective liner provide mechanical stability during wear.

The drug diffuses from the adhesive into the skin by diffusion, with the release rate governed by drug properties, adhesive composition, skin condition, and temperature. Drug stability within the adhesive is a key consideration, as interactions with the adhesive or excipients can affect potency and shelf life. Compatibility between the drug and adhesive is routinely evaluated during development.

DIA is used for a range of systemic medications with suitable lipophilicity and molecular size, including nicotine replacement therapy and various analgesics and hormones. DIA enables relatively simple patch architectures with homogeneous drug distribution and, in some cases, higher loading than certain reservoir designs.

Advantages of the DIA approach include straightforward manufacturing, thin and flexible patches, and sustained, predictable release with reliable adhesion. Limitations include potential drug–adhesive interactions, restricted loading for poorly soluble drugs, risk of skin irritation or sensitization, and regulatory challenges to demonstrate long-term stability and safety in the adhesive matrix.

Manufacturing involves blending the drug with the adhesive, coating a thin film onto a patch backing, and applying a protective liner. Quality control tests include in vitro drug release, skin permeation, adhesion strength, and stability assessments. Regulatory review focuses on dosing consistency, biocompatibility, and therapeutic benefit.