Principles of Topical Therapy

Unilateral treatment allows for easier treatment response evaluation than with systemic treatment
Topical preparations/formulations consist of a drug in a non-active base/vehicle
Drugs used on skin must be dissolved or suspended in a vehicle
- The choice of drug depends on the diagnosis
- The choice of vehicle depends on the state of the skin
- The drug will be transferred from the vehicle to stratum corneum
- The base determines the rate at which the drug is absorbed through the skin
An overview of different types of topical formulations. From https://plasticsurgerykey.com/other-topical-medications-2/
Vehicles
- Liquid vehicles
  - Water
  - Ethanol
  - Glycerol
- Solid vehicles (powders)
  - Zinc oxide
  - Titanium oxide
  - Talc
  - Starch
- Fatty vehicles (greases)
  - Vegetable fats
  - Animal fats
  - Mineral oils
  - Petrolatum
Types of topical preparations

Topical preparations
- Solution
  - Drug dissolved in a liquid solvent like alcohol or water
  - Convenient to apply (can be applied with a dropper)
- Lotions
  - Water-based emulsion
  - Thicker than solution
  - Good for hairy skin
  - They cool inflammatory lesions and dry exudative lesions
- Creams
  - A semisolid emulsion of water in oil or oil in water
  - Thicker than lotion
  - Good for weeping lesions
  - When applied with wet compress -> good for inflamed skin
- Ointments
  - Semisolid grease or oil, without water
  - Good for scaly or dry lesions
  - When applied with wet compress -> good for inflamed skin
- Gels
  - Soft, semisolid preparation
  - Liquefy on contact with the skin
- Foam
  - Aerosolized solution with a pressurized propellant
  - Good for hairy skin
- Powders
  - Solid
  - For lesions in moist or intertriginous areas
- Cooling paste
  - Contains oil, water and powder
  - Often contains zinc oxide
  - Cools inflamed skin
Dressings
- Protect open lesions, facilitate healing, increase drug absorption
- Non-occlusive dressings (wet dressings)
  - Dressings wetted with saline or water
  - Applied to the lesion and removed when the solution has evaporated
  - Good for thick or crusted lesions
  - Good for oozing lesions
- Occlusive dressings
  - Increase the absorption and effectiveness of topical therapy
  - Can be applied over topical preparations to increase absorption
  - Can be applied to open wounds to allow them to heal
Moisturizing agents (emollients)
- Restore water and oil to skin and help maintain skin hydration
- More effective in slightly wet skin, like after a shower
- Available as lotions, creams, ointments, etc.
- Indicated in dry skin conditions
- Contains occlusives and humectants
- Humectants
  - These agents attract water, increasing the water-holding capacity of the stratum corneum
  - Glycerine
  - Urea
  - Lactic acid
  - Glycolic acid
- Occlusives
  - Form a physical barrier to prevent water loss
  - Waxes
  - Petrolatum
  - Oils
Drying agents (powders)
- To treat excessive moisture, like between skin folds, the groin, etc
- Corn starch
- Talc
Topical agents to alleviate pruritus
- Pramoxine
- Hydrocortisone
- Menthol
- Phenol
Keratolytics
- These agents facilitate exfoliation of epidermal cells
- Used to treat hyperkeratotic diseases like
  - Psoriasis
  - Seborrheic dermatitis
  - Acne
- Urea
- Salicylic acid
- Lactic acid
- Glycolic acid
Steroids
- Widely used in dermatology
- Indications
  - Cutaneous lupus erythematosus
  - Psoriasis
  - Lichen
  - Contact dermatitis
  - Atopic dermatitis
  - Allergic skin reactions
- Mostly used steroids
  - Hydrocortisone (low potency)
  - Triamcinolone (medium potency)
  - Clobetasol (high potency)
- Side effects
  - Skin atrophy
  - “Steroid acne”
  - Striae
  - Contact allergy
  - “Steroid rosacea” = perioral dermatitis
    - When potent steroids are used on the face
    - Telangiectasias
    - Papules, pustules
Topical antibiotics
- Mostly used in acne
- Tetracyclines
- Metronidazole
- Erythromycin
- Clindamycin
- Bacitracin
Silver nitrate
- Low concentration – debride wounds
- High concentration – cauterizes bleedings in wounds
Imiquimod
- Immune regulator
- Indications
  - Warts
  - BCC
  - Actinic keratosis
Topical calcineurin inhibitors
- Tacrolimus
- Pimecrolimus
- Indications
  - Atopic dermatitis
5-fluorouracil
- Indications
  - Actinic keratosis
  - BCC
  - Warts
Fingertip units (FTU)
- 1 FTU = the amount of topical preparation expressed from a tube when applied from the distal skin-crease to the tip of the index finger
- 1 FTU is approx. 0,5 g
- 1 FTU covers approx. 300 cm2, which is enough for one hand
- 2,5 FTU covers the face and neck
- Fingertip units are useful when telling patients how much they should use of a preparation