Skin Infections

Superficial bacterial infections, e.g. impetigo, eczema, are commonly staphylococcal or streptococcal. They are treated by a topical antimicrobial for less than 2 weeks and applied twice daily after removal of crusts that prevent access of the drug, e.g. by a povidone-iodine preparation. Very extensive cases need systemic treatment.

Topical fusidic acid and mupirocin are preferred (as they are not ordinarily used for systemic infections and therefore development of drug resistant strains is less likely to have any serious consequences). Framycetin and polymyxins are also used. Absorption of neomycin from all topical preparations can cause serious injury to the eighth cranial nerve. It is also a contact sensitiser.

When prolonged treatment is required, topical antiseptics (e.g. chlorhexidine) are preferred and bacterial resistance is less of a problem.

Combination of antimicrobial with a corticosteroid (to suppress inflammation) can be useful for secondarily infected eczema.

The disadvantages of antimicrobials are contact allergy and developments of resistant organisms (which may cause systemic, as well as local, infection). Failure to respond may be due to development of a contact allergy (which may be masked by corticosteroid).

Infected leg ulcers generally do not benefit from long-term antimicrobials although topical metronidazole is useful when the ulcer is malodorous due to colonisation with Gram-negative organisms. An antiseptic (plus a protective dressing with compression) is preferred if antimicrobial therapy is needed.

Nasal carriers of staphylococci may be cured (often temporarily) by topical mupirocin or neomycin plus chlorhexidine.

Deep bacterial infections, e.g. boils, generally do not require antimicrobial therapy; but if they do it should be systemic. Cellulitis requires systemic chemotherapy initially with benzylpenicillin and flucloxacillin.

Infected burns are treated with a variety of antimicrobials, including silver-sulphadiazine and mupirocin.

Fungal infections; superficial dermatophyte or Candida infections purely involving the skin can be treated with a topical imidazole (e.g. clotrimazole, miconazole). Pityriasis versicolor, a yeast infection, primarily involves the trunk in young adults; it responds poorly to imidazoles but topical terbinafine or selenium sulphide preparations are effective; severe infection may require systemic itraconazole. Invasion of hair or nails by a dermatophyte or a deep mycosis requires systemic therapy; terbinafine is the most effective drug. Terbinafine and griseo-fulvin are ineffective against yeasts, for which itraconazole is an alternative. Itraconazole can be used in weekly pulses each month for 3-4 months; it is less effective against dermatophytes than terbinafine.

Virus infections. Topical antivirals: aciclovir (acyclovir). (see p. 257). Aciclovir is used systemically for the potentially severe infections, e.g. eczema herpeticum.

Parasite infection. Topical parasiticides (see Table 16.3 for details).

Disinfection and cleansing of the skin. Numerous substances are used according to circumstances:

• for skin preparation prior to injection: ethanol or isopropyl alcohol

• for disinfection: chlorhexidine salts, cationic surfactant (cetrimide), soft soap, povidone-iodine (iodine complexed with polyvinylpyrollidone), phenol derivatives

(hexachlorophene, triclosan), and hydrogen peroxide.

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