What are examples of transdermal drug delivery systems (TDDs)?

• A. Suppositories
• B. Oral tablets
• C. Inhalers
• D. Ointments, creams, gels, transdermal patches

Answer: (D)

Delivering a drug through the skin to reach the bloodstream is the defining idea of a transdermal system. The classic example is a transdermal patch, which is designed to release drug steadily over hours or days and maintain systemic levels without frequent dosing. Semi-solid formulations like ointments, creams, and gels can also be used as transdermal systems when they’re formulated to permeate the skin and deliver drug systemically rather than just locally. In contrast, suppositories deliver via the rectal route, oral tablets go through the gastrointestinal tract, and inhalers deliver to the lungs. That combination of patch-based delivery and skin-penetrating topical formulations makes them the clear examples of transdermal drug delivery systems.