Medicines Design & Manufacture - Topical Medicines Notes

Learning Outcomes

  • Understand the structure of the skin relevant to topical formulations.

  • Knowledge of various drugs delivered topically and their targeted skin regions.

  • Familiarity with classes of semi-solid preparations used as emollients and topical vehicles.

  • Awareness of two recognized mechanisms of emolliation.

Functions of the Skin

  • Protection against:

    • Pollution

    • Temperature

    • Humidity

    • Radiation

  • Functions:

    • Protects internal organs

    • Limits passage of chemicals

    • Stabilizes blood pressure and temperature

    • Mediates sensory responses (heat, cold, touch, pain)

    • Expresses emotions (fear, anger, embarrassment, anxiety)

    • Indicates human characteristics (color, hair, odor, texture)

  • Susceptibility to Damage:

    • Physical: Cuts, bruises, burns, radiation exposure

    • Chemical: Bites, stings, detergents, pollutants

    • Biological: Microorganisms (bacteria, fungi, viruses)

Main Regions of the Skin

  • Epidermis:

    • Multilayered and varies in thickness; 0.8 mm (palms/soles) to 6 mm (eyelids)

    • Stratum Corneum:

    • Dead, dense, and impermeable layer

    • Swells in water (maceration) 3-5 mm thick

  • Dermis:

    • Matrix with connective tissue (collagen, elastin)

    • Contains nerves, blood vessels, lymphatics, and skin appendages

  • Subcutaneous Tissue:

    • Provides mechanical cushion and thermal barrier

    • Synthesizes and stores chemicals

Skin Appendages

  • Types:

    • Eccrine Sweat Glands: Produce sweat (pH 4.0-6.8), regulate heat

    • Apocrine Sweat Glands: Develop at hair follicles, oily secretions aid in smell

    • Sebaceous Glands: Produce sebum from cell disintegration (not present on lips/palms/soles)

    • Hair Follicles: Support hair growth

Drug Delivery Approaches

  • Barrier Manipulation of Stratum Corneum:

    • Uses antibacterials, sunscreens, and emollients

  • Direct Delivery to Viable Tissues:

    • Avoids oral/systemic routes

    • Example: Transdermal systems for various conditions (motion sickness, hormonal therapy)

Penetration Routes and Treatments


  • Surface Route:

    • Drugs diffuse from the stratum corneum and are used for camouflage, insect repellent, antimicrobial treatments.

  • Transappendageal Route:

    • Through pilosebaceous units or eccrine glands for treatments like antibiotics or exfolients.

  • Viable Epidermis/Dermis Route:

    • Effective for anti-inflammatories, anesthetics, antipruritics, antihistamines, and phototherapies.

Treatments of the Stratum Corneum

  • Emollients:

    • Soothing and hydrating agents for dry or scaling disorders; frequent application due to short-lived effects.

    • Examples: Aqueous Cream BP, Neutrogena™.

Treatments for Skin Appendages

  • Antiperspirants for Hyperhydrosis:

    • Example: Aluminium chloride hexahydrate.

  • Treatment for Acne:

    • Topical exfoliants like salicylic acid, benzoyl peroxide; antibiotics.

  • Fungal Infections:

    • Localized treatments using imidazoles.

Treatments for Viable Epidermis/Dermis

  • Drug Delivery Approaches:

    • Use of pro-drugs for efficient delivery to receptors.

    • Anti-inflammatories: Steroidal, NSAIDs (e.g., Diclofenac).

    • Anaesthetics: Local relief of pain.

    • Antihistamines: Effective for insect bites/stings.

    • PUVA and PDT: For psoriasis and skin cancer treatment.

Formulation Types

  • Liquid Preparations:

    • Simple soaks/baths, liniments, lotions for various skin conditions.

  • Ointments:

    • Greasy preparations with various bases (hydrocarbon, fats, emulsifying).

  • Creams:

    • Oily and aqueous formulations designed for hydration and absorption.

  • Examples of Solid/Semisolid Preparations:

    • Zinc and salicylic acid paste for hyperkeratotic disorders.

    • Emulsifying ointment for dry skin conditions.

Further Reading Recommendations

  • Barry, B.W. on transdermal drug delivery.

  • Williams, A.C. on topical and transdermal drug delivery.