Design of Transdermal Drug Delivery Systems (TDDS)

What is the primary reason why hydration of the skin is necessary for TDDS?

According to Fick's Law, what is the rate of drug transport across the skin directly proportional to?

What is the main difference between matrix-based and reservoir-based TDDS?

Which of the following is a characteristic of chemical penetration enhancers?

What is the purpose of a penetration enhancer in a TDDS?

What is the effect of increasing the drug concentration in the formulation vehicle on the rate of drug transport across the skin?

What is the main advantage of using a solid formulation in a TDDS?

What is the purpose of using a matrix-based TDDS design?

What is the effect of increasing the surface area of the skin to which a TDDS is exposed on the rate of drug transport?

What is the purpose of using a reservoir-based TDDS design?

Immediate and Controlled Release

Immediate release: needles dissolve, providing an immediate effect
Controlled release: depends on the polymer used, providing a sustained effect

Design of TDDS

Basic components:
- Outer backing film: occlusive, water-resistant, and drug-impermeable, with a low moisture vapor transmission rate
- Thickness: 2-3 mm, transparent or pigmented film, usually beige
- Materials: polypropylene, polyethylene, polyolefin
Drug is dispersed or dissolved in an inert polymeric matrix, providing support and control for drug release
Rate-controlling membranes (in reservoir design only)
Adhesive layer: sticks the patch to the skin, e.g. polybutyl acrylate

Matrix (Monolithic) TDDS

Polymer used is usually solid
Increases hydration of skin due to sweating, increasing skin absorption
Skin hydration is essential for drug dissolution, but creams or moisturizers should be avoided as they increase hydration excessively

Kinetics of Transdermal Diffusion

Follows Fick's Law: dQ/dt= DAK (Cvehicle– CP) / h
Rate of drug transport across the skin is directly proportional to:
- Drug oil/water partition coefficient (K)
- Drug concentration in the formulation vehicle (Cvehicle)
- Surface area of the skin (A)
Rate of drug transport is inversely proportional to the thickness of SC (h)

Formulation Factors

TDDS design: Matrix vs. Reservoir
Drug formulation: Solid vs. Liquid, with solid providing faster absorption
Penetration enhancers:
- Chemical Enhancers (Passive): reversibly damage or alter the stratum corneum to reduce diffusional resistance, e.g. acetone, ethanol, PEG, PG, azone, DMSO
- Selection based on efficacy, toxicity, compatibility

Learn about the design of transdermal drug delivery systems, including immediate and controlled release, and their components. Understand the materials and properties of outer backing films.