3 The technology
3.1 Topical corticosteroids have anti-inflammatory and immunosuppressive effects. The mechanism of the anti-inflammatory activity of topical steroids in general is unclear, although various symptomatic components of the inflammatory pathway are known to be suppressed.
3.2 Thirty preparations of topical corticosteroids are included in this appraisal (see Appendix D). Topical corticosteroids are classified according to their potency. This is determined by the amount of vasoconstriction a topical corticosteroid produces and the degree to which it inhibits inflammation (a more potent product increases suppression to the inflammatory pathway). In the UK, four potencies are recognised: mild, moderately potent, potent and very potent. Across the different potencies, products have different formulations and different strengths (for example, 0.025%, 0.1%, 0.5%) and are available in various preparations (for example, ointment, cream, lotion, foam).
3.3 The most widespread side effect of topical corticosteroid treatment is skin atrophy, where the skin becomes thin and may become easily bruised. This is more likely to occur on areas where the skin is already thin, such as the face or flexures. Absorption is greatest in these areas and therefore the use of potent steroids on these sites should generally be avoided. The skin may recover gradually after stopping treatment, but the original structure may never return. Prolonged or excessive use of potent steroids causes the dermis to lose its elasticity and stretch marks (striae) to appear, which are permanent. Children, especially babies, are particularly susceptible to side effects. The more potent corticosteroids are contraindicated for infants less than 1 year old. For full details of side effects and contraindications, see the Summaries of Product Characteristics (SPCs) for the topical corticosteroids.
3.4 Guidelines from the British Association of Dermatologists suggest that the best way of using topical corticosteroids is probably twice daily for 10–14 days when the eczema is active, followed by a 'holiday period' of emollients only. The National Prescribing Centre recommends that, in general practice, topical corticosteroids be used in short bursts (for 3–7 days) to treat exacerbations of disease.
3.5 There are varying recommendations about the frequency of application. The British National Formulary (BNF) states that "corticosteroid preparations should normally be applied once or twice daily. It is not necessary to apply them more frequently". Although there are few empirical data to assess the patterns of prescribing with respect to frequency of application, it appears that a twice-daily regimen is the most widespread approach to the use of topical corticosteroids in atopic eczema. However, the SPCs for some of the topical corticosteroids indicate that some are licensed for more frequent use (up to four times a day), and two products are licensed for use only once a day in atopic eczema. For individual posologies, see Appendix D.