4.1 DDS

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Questions and Answers

What is one reason for the topical application of drugs?

Enhancing internal organ function

Increasing blood circulation in limbs

Treating systemic bacterial infections

Protecting injured skin from the environment (correct)

Which of the following is NOT a dosage form for topical administration?

Syrups (correct)

Lotions

Ointments

Gels

Which layer of the skin is primarily responsible for producing new keratinocytes?

Stratum corneum

Stratum spinosum

Stratum basale (correct)

Stratum granulosum

What role do Langerhans cells serve in the epidermis?

Skin's immune defense Signup and view all the answers

Which skin layer acts as the primary protective barrier?

Stratum corneum Signup and view all the answers

What percentage of the epidermis is made up of keratinocytes?

80% Signup and view all the answers

Which of the following is a characteristic of the dermis layer of the skin?

It contains sweat glands and hair follicles Signup and view all the answers

What is one of the physiological roles of the skin?

Excreting substances through sweat Signup and view all the answers

What is the dominant route for drug permeation through the stratum corneum?

Paracellular route Signup and view all the answers

Why is lipophilicity a key consideration for topical drug formulation?

Lipophilic drugs can permeate better through the stratum corneum. Signup and view all the answers

What happens to a drug once it passes through the stratum corneum?

It quickly reaches systemic absorption in the dermis. Signup and view all the answers

What primarily limits the contribution of transappendageal transport to drug permeation?

The small surface area covered by appendages Signup and view all the answers

How does skin condition affect drug penetration?

Damaged skin can significantly alter drug penetration. Signup and view all the answers

What impact does hydration have on drug permeation through the stratum corneum?

Hydration enhances drug permeation by expanding pathways in the stratum corneum. Signup and view all the answers

What characterizes the drug metabolism in the viable epidermis?

It can lead to a significant cutaneous first-pass effect. Signup and view all the answers

Which factor influences the permeability of drugs across skin among individuals?

Interpatient variability Signup and view all the answers

How do lipophilic and hydrophilic drugs differ in terms of permeation through the stratum corneum?

Lipophilic drugs permeate readily due to the lipid-rich nature of the stratum corneum. Signup and view all the answers

What role does occlusion play in drug permeation?

It enhances skin hydration and increases drug permeation. Signup and view all the answers

What is the primary component of the stratum corneum that acts as a barrier to drug penetration?

Intercellular lipids Signup and view all the answers

Which of the following best describes corneocytes?

Flat, dead keratinocytes with interspersed lipid sheets Signup and view all the answers

What is the role of the Natural Moisturizing Factor (NMF) found in corneocytes?

Attracting water to maintain hydration Signup and view all the answers

How are desmosomes important for the stratum corneum's function?

They bind corneocytes together, contributing to structural integrity. Signup and view all the answers

What occurs during the continuous renewal process of corneocytes?

They slough off after approximately 14 days. Signup and view all the answers

In which layer of the skin are eccrine sweat glands primarily involved?

Dermis Signup and view all the answers

What is the estimated thickness difference between the dermis and epidermis?

40 times thicker Signup and view all the answers

Which of these is NOT a function of the acid mantle on the skin surface?

Thermoregulation Signup and view all the answers

What influence does damaged skin have on drug permeation?

It allows for faster drug penetration. Signup and view all the answers

What role does subcutaneous fat play in drug absorption?

It acts as a reservoir for lipophilic drugs. Signup and view all the answers

Which drug delivery route is considered the primary method for drug permeation through the skin?

Transepidermal Signup and view all the answers

What is a possible consequence of disruption to the skin's acid mantle?

Decreased skin hydration Signup and view all the answers

Which component primarily provides the skeleton structure for the stratum corneum?

Keratin and filaggrin Signup and view all the answers

Which of the following drug types needs to penetrate the stratum corneum to reach its target site?

Topical corticosteroids for anti-inflammatory effects Signup and view all the answers

Study Notes

Topical Drug Application

Topical drugs are applied directly to the skin for various reasons, including treating skin conditions (eczema, psoriasis), relieving pain (e.g., diclofenac gel), and systemic delivery (e.g., nicotine patches).

Topical Dosage Forms

Liquids: Solutions, lotions, tinctures, collodions, medicated shampoos
Semisolids: Ointments, creams, pastes, gels
Solids: Powders, sticks
Others: Aerosols, foams, dressings, tapes, plasters

Skin Anatomy and Physiology

Skin is the largest organ, varying in thickness, weighing approximately 3-4 kg in adults.
Protective Barrier: Protects against microorganisms, chemicals, radiation (UV rays), shocks, and injury.
Physiological Roles: Regulates temperature, excretes substances, and is involved in drug absorption.
Complex Structure: Physiologically and biochemically intricate.

Skin Layers and Appendages

Three primary layers: epidermis, dermis, subcutaneous fat.
Includes sweat glands (apocrine, eccrine), hair follicles.

Epidermis

Outermost layer, stratified squamous epithelium; constantly renewing.
Varies in thickness across different body regions.
Primarily composed of keratinocytes (80%), containing keratin (strength, toughness).
Other cell types: Langerhans cells (immune defense), melanocytes (melanin production, UV protection, skin color), Merkel cells (fine touch sensation).
Layers: Stratum corneum (outermost, primary protective barrier), stratum lucidum (thin, palms/soles), stratum granulosum (lipid production), stratum spinosum, stratum basale (deepest, new keratinocyte generation).

Keratinocytes

80% of epidermis, high keratin content.
Organized into strata, contributing to skin barrier properties.
Viable (living) and non-viable (dead) layers.
Viable: All layers except stratum corneum.
Non-viable: Stratum corneum, dead cells.

Stratum Corneum

Crucial barrier to drug penetration.
Brick-and-mortar structure: Corneocytes (dead keratinocytes) are "bricks," intercellular lipids are "mortar."

Corneocytes

Flat, enlarged, overlapping dead keratinocytes, interspersed with lipid sheets.
Lack nucleus and organelles, contain 10-20% water.
Rich in keratin and filaggrin, structural proteins.
Contain Natural Moisturizing Factor (NMF), low molecular weight polar compounds, attracting water from dermis.

Intercellular Lipids

Composed of ceramides, free fatty acids, cholesterol.
Crucial for corneocyte binding, limiting permeation (in/out) and preventing water loss.
Produced by stratum granulosum.

Desmosomes

Specialized junctions binding corneocytes together, for structural integrity and barrier function.
Breakdown leads to skin flaking.

Skin Renewal

Corneocytes slough off after approximately 14 days.
Continuous shedding, replaced by cells from the basale layer.
Turnover time varies between body regions.

Dermis

Located beneath the epidermis, much thicker.
Connective tissue matrix (support, strength).
Responsible for skin structure and elasticity.
Contains nerves, appendages (sweat/hair follicles), blood/lymphatic vessels.
Drug absorption into systemic circulation possible.

Subcutaneous Fat

Deepest layer, adipose tissue.
Can act as a drug reservoir, delaying/slowing absorption or serving as a depot.

Sweat and Sebaceous Glands

Eccrine sweat glands: thermoregulation
Apocrine sweat glands: secrete into hair follicles
Sebaceous glands: associated with follicles, produce sebum (lipid mixture, waterproofing, lubrication).

Acid Mantle

Acidic environment (pH 4.5-6.2) on skin surface.
Created by fatty acids in sebum.
Protective functions: antimicrobial, orderly desquamation, lipid lamellae formation.
Dependent on optimal pH.

Hair Follicles

Present in most body areas (except lips, palms, soles).
Can act as drug penetration pathways, bypassing stratum corneum to some extent.

Drug Transport Mechanisms

Some drugs act on skin surface.
Others penetrate layers to target sites.
Examples: Exfoliants (stratum corneum), antiperspirants/antimicrobials/depilatories (appendages), topical corticosteroids (deeper layers).

Drug Permeation Challenges

Skin's primary function is protection, resulting in slow permeation.
Damaged skin allows faster permeation.
Formulations temporarily disrupt stratum corneum to enhance permeation.

Routes of Drug Permeation

Transepidermal: Primary, through epidermal layers.
Transappendageal: Less significant, via appendages.

Transepidermal Transport

Stratum Corneum as Major Barrier: Drugs must penetrate this layer to reach dermis.
Transcellular: Through corneocytes; polar pathway.
Paracellular: Around corneocytes, through lipid lamellae; non-polar pathway.

Lipophilicity & Viable Layers

Lipophilic drugs prefer permeation.
Viable layers offer less resistance to penetration.

Systemic Absorption

Drug absorption into blood/lymph at dermis layer.

Transappendageal Transport

Appendages (hair follicles, sweat glands) offer easier drug access.

Factors Influencing Drug Permeation

Biological factors: Interpatient variability, skin condition (healthy/diseased), drug metabolism, age, drug binding.
Physical-Chemical factors: Hydration, occlusion, drug lipophilicity, dosage form properties.

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Description

Explore the intricate world of topical drug applications and the anatomy of skin. This quiz covers the various types of topical dosage forms and delves into the skin's structure and functions. Test your understanding of how these elements interact in medical treatments.