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Basics of medical therapy—topical treatments
The treatment of skin disease includes topical, systemic, intralesional, radiation and surgical modalities. Specific treatments are detailed below. First is an overview of dermatological therapies.
Topical therapy
Topical treatment has the advantage of direct delivery and reduced systemic toxicity. It consists of a vehicle or base, which often contains an active ingredient ( Table 12.1 ).
Table 12.1
An overview of topical medicaments
| Drug | Indications | Pharmacology |
|---|---|---|
| Corticosteroids | Eczemas, psoriasis, lichen planus, discoid lupus erythematosus, sunburn, pityriasis rosea, mycosis fungoides, photodermatoses, lichen sclerosus | Mode of action is through vasoconstrictive, anti-inflammatory and antiproliferative effects; medication is available in different strengths; side effects need to be considered |
| Antiseptics | Skin sepsis, leg ulcers, infected eczema | Chlorhexidine, benzalkonium chloride, silver nitrate and potassium permanganate are used |
| Antibiotics | Acne, rosacea, folliculitis, impetigo, infected eczema | Chlortetracycline, neomycin, bacitracin, polymixin B, retapamulin, fusidic acid and mupirocin; resistance and sensitization are problems Metronidazole is used for rosacea |
| Antifungals | Fungal infections of the skin, Candida albicans infections | Nystatin, clotrimazole, miconazole, econazole, terbinafine, ketoconazole and amorolfine |
| Antiviral agents | Herpes simplex, herpes zoster | Aciclovir, penciclovir |
| Parasiticidals | Scabies, lice | Benzyl benzoate, permethrin and malathion for scabies; malathion and permethrin for lice—applied as a lotion or shampoo |
| Coal tar | Psoriasis, eczema | Presumed anti-inflammatory and antiproliferative effects; available as creams, shampoos and in paste bandages |
| Dithranol | Psoriasis | Antiproliferative effects; available as creams, pastes and ointments |
| Vitamin D analogues | Psoriasis | Calcitriol, calcipotriol and tacalcitol inhibit keratinocyte proliferation and promote differentiation |
| Keratolytics | Acne, scaly eczemas | Salicylic acid, benzoyl peroxide and tretinoin |
| Retinoids | Acne, psoriasis | Isotretinoin (acne), tazarotene (psoriasis) |
| Topical immunomodulators (calcineurin inhibitors) | Atopic eczema (and off-licence use in other diseases) | Tacrolimus and pimecrolimus |
Vehicles are defined as follows:
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Lotion. A liquid vehicle, often aqueous or alcohol-based, which may contain a salt in solution. A shake lotion contains an insoluble powder (e.g. calamine lotion).
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Cream. A semisolid emulsion of oil-in-water; contains an emulsifier for stability and a preservative to prevent overgrowth of microorganisms.
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Gel. A transparent semisolid, non-greasy aqueous emulsion.
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Ointment. A semisolid grease or oil, containing little or no water but sometimes with added powder. No preservative is usually needed. The active ingredient is suspended rather than dissolved.
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Paste. An ointment base with a high proportion of powder (starch or zinc oxide) producing a stiff consistency.
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Medicated plaster. The steroid betamethasone valerate is available as a medicated plaster (Betesil) than can be adhered to a specific area of an inflammatory dermatosis.
Online, The Merck Manual gives details of topical treatments (search under ‘dermatologic disorders’, access via http://www.merckmanuals.com ).
Pharmacokinetics
Not all potentially useful drugs are suitable for topical use. The ability of a drug to penetrate the epidermis depends on several factors. These include:
- ●
The drug’s molecular size and structure and its lipid/water solubility
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The vehicle used and whether application is occluded
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The site on the body—absorption is greatest through the eyelid and genitalia
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Whether or not the skin is diseased.
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