Therapeutic properties of the vehicle

Lotions evaporate and cool the skin and are useful for inflamed or exudative conditions, e.g. for wet wraps (p. 37). The high water content of a cream means that it mostly evaporates; it is also non-greasy and easy to apply or remove. Ointments are best for dry skin conditions such as eczema. They rehydrate and occlude, but being greasy are difficult to wash off and are less acceptable to patients than creams. Pastes are ideal for applying to well-defined surfaces, such as psoriatic plaques, but are also hard to remove.

Quantities required

One application to the whole body requires 15–20 g of ointment. The adult face or neck requires 1 g, trunk (each side) 3 g, arm 0.5 g, hand 0.5 g, leg 3 g and foot 1 g. A useful guide for patients is the ‘fingertip unit’ (FTU) – the amount of cream or ointment that can be applied to the terminal phalanx of the index finger (Fig. 1). One FTU equals 0.5 g. The weekly amount required for the twice-daily use of an emollient in an adult is 250 g. Doctors often underestimate the quantities needed.

Fig. 1 The fingertip unit (FTU) = 0.5 g.

The safe maximum amount varies with the strength of the steroid, the age of the patient and the length of treatment. For 1% hydrocortisone, adults can use 150–200 g/week, but children can use only 60 g and babies as little as 20 g. Creams/ointments are applied twice daily except for mometasone, fluticasone and tacalcitol, which are used once daily.

Pharmacokinetics

The ability of a drug to penetrate the epidermis depends on several factors. These include:

Emollients

Emollients help dry skin conditions such as eczema and ichthyosis by re-establishing the surface lipid layer and enhancing rehydration of the epidermis. Common emollients include emulsifying ointment, Aveeno, Diprobase, Doublebase, E45, Epaderm, Hydromol, Ultrabase and Unguentum M creams. Sometimes emollients contain urea (Aquadrate, Eucerin) or antimicrobials (Dermol, Eczmol). Oils added to bath water can also help, e.g. Aveeno, Balneum, Dermol, Diprobath, Doublebase, Emulsiderm, Hydromol and Oilatum.

Dressings and hospital admission

Many departments have treatment centres where daily dressings and ultraviolet (UV) treatments are given. If outpatient management is unsuccessful, hospital admission may be needed. Dressings, for either the outpatient or the inpatient, consist of stockinette gauze applied to the trunk or limbs after the ointments have been put on. These must be changed once or twice a day. Leg ulcer dressings may be changed less frequently, depending on the type of application used.

Bandages impregnated with tar are sometimes helpful for leg ulcers and eczema. Many types of paraffin gauze, hydrocolloid and alginate dressing are now available for leg ulcers (p. 73).

Topical steroids

A summary of the indications for topical treatment with corticosteroids is given in Table 1. The relative potencies of the more commonly prescribed preparations are shown in Table 2.

Table 2 Relative potencies of topical steroids

Side-effects of topical steroid therapy

The use of topical steroids carries the potential for harmful side-effects. These include: