The most common skin diseases are dermatitis (eczema), acne, psoriasis, skin cancer (usually managed surgically), viral warts and urticarias (which can be allergic or non-allergic in nature).
Eczema is an inflammatory disease of the skin, defined by the presence of epidermal intercellular oedema or spongiosis, and can be the result of:
exogenous irritants and contact allergens,
adverse responses to certain drugs.
Drugs used to treat dermatitis and their targets are shown in Fig. 23.1 .
Acne affects the pilosebaceous unit and occurs in anatomical sites where these are most numerous, such as on the face, back and chest. Acne is characterized by the presence of keratin plugs in the sebaceous duct openings, known as comedones . Acne may also involve the presence of inflammatory papules, pustules, nodules, cysts and scars. Acne is stimulated by androgens, which is why it usually occurs in puberty, and why the antiandrogen cyproterone is often used in females with acne (see Chapter 17 for an understanding of drugs and endocrine function). The drugs used to treat acne and their targets are shown in Fig. 23.2 .
Psoriasis is a genetic skin disorder that can be precipitated by stress, infection, damage from ultraviolet light or trauma. In psoriasis, the turnover rate of skin is much greater than normal, and this disease is characterized by the following:
Thickened skin plaques
Dilated capillaries in the dermis (these might act to initiate psoriasis or as nourishment for hyperproliferating skin)
An infiltrate of inflammatory cells, especially lymphocytes and neutrophils, in the epidermis and dermis, respectively
Drugs used to treat psoriasis and their targets are shown in Fig. 23.3 .
Treatment of skin disorders
Preparations of topical drugs for use on skin
Drugs applied to the skin are delivered by a variety of vehicles such as ointments, creams, pastes, powders, aerosols, gels, lotions and tinctures. The choice of the vehicle is dependent on a number of factors:
The solubility of the active drug
The ability of the drug to penetrate the skin
The stability of the drug-vehicle complex
The ability of the vehicle to delay evaporation, this being greatest for ointments and least for tinctures
Emollients are used to soothe and hydrate the skin. A simple preparation is an aqueous cream, which is often as effective as more complex drugs. Most creams are thin emollients, whereas a mixture of equal parts soft white paraffin and liquid paraffin is a thick emollient. Camphor, menthol and phenol preparations have antipruritic effects, whereas zinc-based and titanium-based emollients have mild astringent (contracting) effects.
Mechanism of action – Emollients hydrate the skin and reduce transepidermal water loss.
Route of administration – Topical. Many emollients can be added to bath water.
Indications – Emollients are used for the long-term treatment of dry scaling disorders and should be used liberally in the management of eczema and psoriasis.
Contraindications – None.
Adverse effects – Some ingredients, such as lanolin or antibacterials, may induce an allergic reaction.
Examples of corticosteroids include clobetasol propionate, betamethasone, clobetasol butyrate and hydrocortisone ( Table 23.1 ).
|I (very potent)
|Betametasone valerate 0.1%
|III (moderately potent)