Which dosage form provides a constant, time released systemic effect by slow absorption through the skin?

Which dosage form provides a constant, time released systemic effect by slow absorption through the skin?

• A. Gels
• B. Ointments
• C. Transdermal patches
• D. Plasters

Answer: (C)

Transdermal patches are designed for systemic delivery through the skin with a controlled release rate. They use a rate-controlling layer or matrix that lets the drug diffuse into the bloodstream at a steady pace, producing a constant plasma concentration over the duration of use. This approach also avoids first-pass metabolism since absorption occurs through the skin rather than the gastrointestinal tract. Gels and ointments are typically applied for local skin effects or variable, non–time-controlled absorption, so they don’t reliably maintain a steady systemic level. Plasters are usually meant for local treatment and don’t inherently provide the same controlled, long-acting systemic delivery as transdermal patches.

Transdermal patches are designed for systemic delivery through the skin with a controlled release rate. They use a rate-controlling layer or matrix that lets the drug diffuse into the bloodstream at a steady pace, producing a constant plasma concentration over the duration of use. This approach also avoids first-pass metabolism since absorption occurs through the skin rather than the gastrointestinal tract. Gels and ointments are typically applied for local skin effects or variable, non–time-controlled absorption, so they don’t reliably maintain a steady systemic level. Plasters are usually meant for local treatment and don’t inherently provide the same controlled, long-acting systemic delivery as transdermal patches.