Cephalosporins allergy skin testing

Simple patch skin testing is naturally most useful in diagnosing contact dermatitis, but it is unreliable for other allergies. Skin prick tests are helpful in specialist hands for diagnosing IgE-dependent drug reactions, notably due to penicillin, cephalosporins, muscle relaxants, thiopental, streptokinase, cis-platin, insulin and latex. They can cause anaphylactic shock. False positive results occur. 

Two of 178 prospective patients, of whom 151 had a history of penicUUn allergy but were negative on peniciUin skin testing, had reactions to a cephalosporin (153). There were 27 who had a positive peniciUin skin test but did not react to a cephalosporin. SimUar results were found by others (154). 

However, a history of peniciUin allergy is often vague, and many studies have suggested that it is an umeliable indicator, which has been confirmed (155). In 62 peniciUin skin-test-positive patients, cephalosporins produced only one reaction of mild urticaria and bronchospasm (156). 

Neither in vitro tests nor skin tests reliably predict cephalosporin allergy (166). The true frequency of allergic reactions in penicillin-allergic patients exposed to cephalosporins has been estimated to be 1 or 2% (167). Nevertheless, when there is a history of penicillin anaphylaxis or other severe IgE-mediated reactions, it is wise to avoid cephalosporins. 

In peniciUin-aUergic patients, oral or parenteral clindamycin may be used. Alternatively, a first-generation cephalosporin, such as cefazohn (1-2 g intravenously every 8 hours), may be used cautiously for patients who have not experienced immediate or anaphylactic penicitlin reactions and are negative for a penicillin skin test. In mild cases in which an oral cephalosporin can be nsed, ce-fadroxU 500 mg twice daily or cephalexin 250-500 mg four times daily is recommended. Other oral cephalosporins, such as cefaclor, cefprozil, and cefpodoxime proxetil, are also effective in the treatment of ceUnhtis bnt are considerably more expensive. In severe cases in which cephalosporins cannot be used because of documented methicihin-resistant staphylococci or severe /3-lactam allergies, vancomycin shonld be administered. 

If a patient has a mild, delayed allergy to penicillin, first-generation cephalosporins (such as cefazolin) are effective alternatives, but they should be avoided in patients with a history of immediate-type hypersensitivity reactions to penicillins (see Table 109-6). The potential for a true immediate-type allergy should be assessed carefully, and a penicillin skin test should be conducted before giving antibiotic treatment to any patient claiming an allergy. 

The diagnostic of immediate-type allergy by skin tests with cephalosporins has been attempted by several groups, but, as already discussed above, does not yield very satisfactory results. Theoretically, it would be much more appropriate to use preformed conjugates of cephalosporins with polylysine. The hemagglutination... 

Immunologic Of 85 patients with a history of penicillin allergy and positive penicillin skin tests 5 (6%) had an adverse drug reaction to a cephalosporin compared with 5 (0.7%) of 726 patients with a history of penicillin allergy but negative penidllin skin tests [7. Presumed IgE-mediated adverse reactions to the cephalosporins occurred in 2 (2%) of the former compared with only 1 (0.1%) of the latter. 

Park MA, Koch CA, Klemawesch P, Joshi A, Li JT. Increased adverse drug reactions to cephalosporins in penicillin allergy patients with positive penicillin skin test. Int Arch Allergy Immunol 2010 153 (3) 268-73. 

Assem ESK, Vickers MR (1974) Tests for penicillin allergy in man. II. The immunological cross-reaction between penicillins and cephalosporins. Immunology 27 255 Assem ESK, Vickers MR (1975) Investigation of the response to some haptenic determinants in penicillin allergy by skin and in vitro allergy tests. Clin Allergy 5 43... 

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