Antibiotics skin tests

In penicillin-allergic patients, oral or parenteral clindamycin may be used. Alternatively, a first-generation cephalosporin such as cefazolin (1 to 2 g IV every 6 to 8 hours) may be used cautiously for patients who have not experienced immediate or anaphylactic penicillin reactions and are penicillin skin test negative. In severe cases in which cephalosporins cannot be used because of documented methicillin resistance or severe allergic reactions to /1-lactam antibiotics, IV vancomycin should be administered. 

The incidence of nonallergic ampicillin eruptions is 40 to 100% in patients with concomitant Epstein-Barr virus (mononucleosis), cytomegalovirus, acute lymphocytic leukemia, lymphoma, or reticulosarcoma. Nonallergic penicillin-associated rashes are characteristically morbilliform (symmetrical, erythematous, confluent, maculopapular) eruptions on the extremities. The onset of typical nonallergic eruptions is more than 72 hours after (3-lactam exposure. The mechanism for the nonurticarial ampicillin rash is not known and is not related to IgE or type I hypersensitivity. Penicillin skin tests are not useful in the evaluation of nonurticarial ampicillin rashes. Patients with a history of nonurticarial ampicillin rashes may receive other (3-lactam antibiotics without greater risk of subsequent serious allergic reactions. 

Clavulanic acid has a very low immunogenic and allergenic potential in animals. The possible impact of its co-administration with other beta-lactam antibiotics is unknown (53). Two patients with IgE-mediated hypersensitivity to oral co-amoxiclav and positive skin tests for clavulanic acid, but not for penicillins, both tolerated oral amoxicillin. One patient was also challenged with clavulanic acid and developed urticaria, conjunctivitis, and bronchial obstruction (54). Since co-amoxiclav has been widely used since its introduction in 1981, the frequency of hypersensitivity reactions is low. The clinical data available on sulbactam and tazobactam are stiU hm-ited and do not allow an assessment of the frequency and pattern of associated hypersensitivity reactions (55). 

A maximum of 20% of subjects with a history of allergylike reactions after administration of a penicillin antibiotic have positive skin or RAST tests (165-167). Tests using benzylpenicillin derivatives or semisynthetic penicillins can almost double positive test results (168,169). Patients with a positive history but negative skin tests run a 1-3% risk of an IgE-mediated reaction and 60% of testpositive patients had evidence of an immediate reaction, including urticaria and angioedema (165). 

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. 

In a patient with a positive skin test or a history of immediate hypersensitivity to penicillin, vancomycin is the agent of choice. Vancomycin, however, kills S. aureus slowly and is regarded as inferior to penicillinase-resistant penicillins for MSSA. Rifampin as an adjunctive therapy is controversial however, this agent, added to vancomycin in refractory or complicated infections in patients with left-sided IE may result in dramatic patient improvement. Generally, antibiotic therapy should be continued for 4 to 6 weeks. Unfortunately, left-sided IE caused by S. aureus continues to have a poor prognosis, with a mortality rate of 25% to 47%. Eor reasons discussed in the following section, those with IE associated with TVDA have a more favorable response to therapy. 

Side effects caused by macrolides are uncommon and only a very few seem to be caused by allergic mechanisms confirmed by positive skin tests. Up to now, in vitro tests have produced only limited evidence that an immune response to these antibiotics can indeed be induced in animals as well as in humans. 

Chakravarty S, Sircar DK (1961) Allergic reactions due to streptomycin corroboration of clinical findings with streptomycin skin tests. Acta Tuberc Scand 41 144-148 Chung CW, Carson TR (1976) Cross-sensitivity in common aminoglycoside antibiotics. Arch Dermatol 112 1101-1107... 

Immediate allergic reactions including anaphylaxis also occur to other aminoglycoside antibiotics with cases recorded for neomycin, gentamycin, tobramycin, framycetin, streptomycin, and dihydrostreptomycin. In some of these cases where tests were undertaken, patch and/or skin tests proved positive to the culprit aminoglycoside, but cross-reactivity with bacitracin has not been reported or, it seems, looked for. 

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