A transdermal therapeutic system (TTS) is a medicated patch that delivers drug molecules through the skin into systemic circulation at a controlled rate. Properly designed, it offers steady plasma levels, fewer peaks and troughs, and convenient, non-invasive dosing.
Why choose a transdermal therapeutic system?
- Sustained, stable exposure: flattens peaks/troughs vs. oral dosing.
- Bypasses first-pass metabolism: can enable lower total doses.
- Convenience & adherence: once-daily to once-weekly replacement.
- GI-friendly: useful when nausea, dysphagia, or GI irritation is an issue.
- Rapid discontinuation: remove the patch to stop further input (drug tail still depends on depot & half-life).
Always follow a clinician’s advice. Not all actives are suitable for the transdermal route.
How a TTS is built (anatomy)
- Backing layer: occlusive, drug-impermeable film that protects the system.
- Drug layer: either a matrix (drug dispersed in polymer) or a reservoir (drug gel behind a rate-controlling membrane).
- Adhesive system: medical-grade PSA providing skin adhesion; may be drug-in-adhesive (DIA).
- Release liner: peeled off before application.
Common designs
- Drug-in-adhesive (DIA) matrix: thin, simple, good comfort; diffusion through adhesive governs rate.
- Multi-layer matrix: separates adhesion from drug control for better kinetics.
- Reservoir + membrane: tighter zero-order control; requires fail-safe to prevent dose dumping.
What makes a molecule “transdermal-ready”?
- Potency: daily dose typically in mg or sub-mg.
- Physicochemical fit: logP ~1–4, MW generally <500–600 Da, non-ionized fraction at skin pH, moderate melting point.