Transdermal Drug Delivery (Patches)

Introduction & scope

• A transdermal drug delivery system (TDDS) — popularly a patch or transdermal therapeutic system (TTS) — is a discrete, self-contained dosage form that, applied to intact skin, delivers drug across the skin (percutaneous absorption) into the systemic circulation at a controlled, predictable rate over hours to days.
• Systemic, not topical — the patch exploits skin as a port for systemic delivery, distinguishing it from topical/cutaneous forms (ointments, creams, gels) whose intent is local action on the skin itself.
• An ER form by a non-oral route — conceptually an extended-release dosage form delivered transdermally — it aims for zero-order input analogous to a slow IV infusion, giving a ≥2-fold reduction in dosing frequency vs immediate-release.
• Prototype & taxonomy — in KDT's route taxonomy the cutaneous (transdermal) route is a systemic route because the therapeutic target is the bloodstream; the prototype is glyceryl trinitrate (GTN) applied as ointment or patch for angina.
• Terminology used interchangeably: TDDS = transdermal drug delivery system; TTS = transdermal therapeutic system (originally an ALZA trademark, now generic); patch = the marketed product.