Dermatological Vehicles and Delivery Systems

Vehicle Fundamentals - Skin's Delivery Crew

• Role: Deliver active drug; protect, hydrate, lubricate skin.
• Ideal Properties: Stable, non-irritating, non-allergenic, compatible, cosmetically acceptable.
• Percutaneous Absorption:
  • Main barrier: Stratum corneum (SC).
  • Pathway: SC → Viable epidermis → Dermis.
  • Key Factors:
    • Drug: ↑Concentration, ↑Lipophilicity, ↓Molecular weight (ideal <500 Da).
    • Vehicle: ↑Occlusion & ↑Hydration = ↑Penetration.
    • Skin: Site (e.g., scrotum > forearm > palm), integrity, age.
  • Fick's Law: $J = -D \frac{dC}{dx}$ (Flux proportional to concentration gradient).

⭐ Occlusion (e.g., by ointments or plastic films) can increase drug penetration up to 100-fold by hydrating the stratum corneum.

Semi-Solid Vehicles - The Goopy Group

• Semi-solid vehicles: topical preps with consistency between solid & liquid. Allow prolonged skin contact, enhance drug delivery & skin hydration.
• Main types: Ointments, Creams, Gels, Pastes. Differ in properties, drug penetration, skin feel, and suitability for various dermatoses.

📌 Ointments: Occlusive. Creams: Choice (O/W or W/O). Gels: Greaseless. Pastes: Protective_&_Powdery.

Liquid & Other Vehicles - Fluid & Fine Forms

• Lotions: Suspensions/solutions of powder in water/alcohol (e.g., calamine).
  • Cooling, soothing, drying via evaporation.
  • Ideal for large, hairy, or intertriginous areas.
  • Types: Shake lotions (require shaking), True solutions (e.g., KMnSO₄).
• Solutions: Drug fully dissolved in solvent (e.g., Burrow's solution - aluminium acetate).
  • Clear, homogenous. For cleansing, antiseptic, astringent effects.
• Powders: Finely divided solids (e.g., talc, zinc oxide, antifungal powders).
  • Absorb moisture, reduce friction, provide cooling.
  • Use: Intertriginous areas, weeping lesions.
• Foams: Pressurized gas bubbles in liquid (e.g., steroid, minoxidil foams).
  • Spread easily, non-greasy. Excellent for hairy areas (scalp).

  ⭐ Foams often enhance drug delivery and patient preference for scalp dermatoses due to ease of application and minimal residue.

• Aerosols/Sprays: Drug in solution/suspension propelled by gas.
  • Convenient for extensive, tender areas, or scalp. Cooling effect.

Vehicle Selection & Advanced Delivery - Smart System Strategies

• Crucial Vehicle Selection Factors:

  • Site Specificity: Scalp (lotions, foams), Face (creams), Intertriginous (powders, creams), Palms/Soles (ointments).
  • Skin Condition:
    • Acute/Oozing: Lotions, creams, soaks.
    • Chronic/Dry/Lichenified: Ointments.
    • Oily/Hairy: Gels, lotions, foams.
  • Drug Properties: Solubility, stability, desired penetration depth.
  • Patient Factors: Age, adherence, cosmetic acceptability.
  • Occlusion: ↑ penetration (e.g., corticosteroids).

• Smart Delivery Systems (Novel Approaches):

  • Vesicular: Liposomes, Niosomes, Transfersomes, Ethosomes.
  • Particulate: Nanoparticles (SLN, NLC), Microsponges.
  • Physical Enhancement: Iontophoresis, Phonophoresis, Microneedles.

⭐ Liposomes and Nanoparticles (e.g., SLN) improve drug localization in skin layers, enhancing efficacy and reducing systemic absorption.

High‑Yield Points - ⚡ Biggest Takeaways

• Vehicle choice is key: match to lesion type (dry/oozing), site, and penetration needs.
• Ointments: Most occlusive & potent; for chronic, dry, hyperkeratotic lesions. Avoid folds.
• Creams: Versatile, less greasy; for many acute/subacute dermatoses.
• Lotions/Solutions: Cooling, least greasy; for large/hairy areas, scalp.
• Gels: Non-greasy, quick-drying; for oily skin, acne, scalp.
• Pastes: Protective, high powder; for oozing lesions, intertrigo.
• Occlusion ↑ drug penetration, potency, and side effects.