Transdermal Drug Delivery System (TDDS)

Introduction

• Topic: Transdermal Drug Delivery System (TDDS)
• Subject: B-Pharmacy 7th Semester
• Presented by: Akash Kumar
• Aim: To cover the topic over two videos; this video includes introduction and factors affecting permeation through skin.

Lecture Constraints

• Presenter using left hand due to right-hand fracture.
• Focus more on spoken explanations.

TDDS Overview

• What is TDDS?
  • A drug delivery system designed to administer drugs through the skin.
  • Keywords: Trans- (across) Dermal (skin).
  • Function: Allows drugs to be absorbed into the bloodstream through the skin.

Components

• Patches:
  • Similar in form to bandages, patches contain drug-filled matrices or reservoirs.
  • Are applied to the skin where the drug penetrates through the dermal layers into the blood vessels.
• Types of Systems:
  • Reservoir System
  • Matrix System

Mechanism of Action

• Application: Particles applied via patches to the skin.
• Absorption: Drug gradually penetrates skin layers, enters blood vessels, and reaches systemic circulation.
• Form: Medicated patches, self-adhesive, maintaining drug concentration over time.

Advantages

• Patient compliance: Easy to use, convenient for self-administration.
• Avoids first-pass metabolism: Direct application to action site, bypassing liver metabolism.
• Non-invasive: Applied externally, no need for injections or oral ingestion.
• Easy termination: Patch can be removed easily if needed.

Disadvantages

• Possible inflammation: Skin irritation at the application site.
• Limited to potent drugs: Only suitable for drugs that can penetrate skin layers effectively.
• Contribution to discomfort: Potential irritation or discomfort, especially behind the ear.

Permeation Through Skin

• Skin Structure:
  • Skin: Largest organ, covering entire body, contains water, protein, fat.
  • Composed of three main layers: Epidermis, Dermis, Subcutis (Subcutaneous Tissue).
  • Blood circulation: 1/3 of all blood in the body is in skin.
• Layers of Skin:
  • Epidermis: Outermost layer (~150 micrometers thick)
    • Stratum Corneum: Outermost, non-viable layer, barrier function.
    • Granulosum, Spinosum, Basale: Viable epidermis layers aiding drug diffusion.
  • Dermis: Middle layer containing connective tissues, blood vessels, nerves, hair follicles, sweat glands.
  • Subcutis: Innermost, connects skin to underlying muscles, stores fat.

Routes of Drug Permeation

• Transfollicular Route:
  • Through hair follicles and sweat glands.
• Transepidermal Route:
  • Through the remaining skin surface, primarily via:
    • Interstitial Route: Through cell junctions.
    • Intracellular Route: Through corneocytes.
    • Mostly hydrophilic drugs through corneocytes; lipophilic drugs through intercellular spaces.
  • Fick's Law of Diffusion: Drug moves from high concentration (patch) to low concentration (blood).

Factors Affecting Permeation

• Physiological Factors:
  • Skin hydration, temperature, thickness, and pH.
• Biological Factors:
  • Skin condition (health/injury), age (young/old), blood flow, species differences.
• Chemical Factors:
  • Drug concentration, solubility, molecular size, ionization state.

Summary

• TDDS provides non-invasive, convenient, and effective drug delivery but is limited to certain potent drugs and may involve skin irritation.
• Understanding skin structure and factors affecting drug permeation is essential for utilizing TDDS effectively.
• Next video will cover formulation approaches and system components in detail.