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Question answered:19/04/07 Warning! this question is over two years old.
A 2006 guideline produced by the Centre for Disease Control and Prevention on the management of patients who have a history of penicillin allergy discusses the use of skin testing:
“An estimated 10% of persons who report a history of severe allergic reactions to penicillin remain allergic. With the passage of time after an allergic reaction to penicillin, the majority of persons who have had a severe reaction to penicillin stop expressing penicillin-specific IgE. These persons can be treated safely with penicillin. The results of many investigations indicate that skin testing with the major and minor determinants of penicillin can reliably identify persons at high risk for penicillin reactions. Although these reagents are easily generated and have been available for >30 years, only benzylpenicilloyl poly-L-lysine (Pre-Pen® [i.e., the major determinant]) and penicillin G have been available commercially. Testing with only the major determinant and penicillin G identifies an estimated 90%-97% of the currently allergic patients. However, because skin testing without the minor determinants would still miss 3%-10% of allergic patients and because serious or fatal reactions can occur among these minor-determinant-positive patients, specialists suggest exercising caution when the full battery of skin-test reagents is not available…”
Recommendations for testing and the procedures for various types of penicillin allergy skin testing are outlined in some detail, and may be accessed by following the link in the references section below. [1]
The Merck Manual contains a chapter on drug hypersensitivity which notes:
“Skin testing: Tests for immediate-type (IgE-mediated) hypersensitivity help diagnose reactions to â-lactam antibiotics, foreign (xenogeneic) serum, and some vaccines and polypeptide hormones. However, typically, only 10 to 20% of patients who report a penicillin allergy have a positive reaction on skin tests. Also, for most drugs (including cephalosporins), skin tests are unreliable and, because they detect only IgE-mediated reactions, do not predict the occurrence of morbilliform eruptions, hemolytic anemia, or nephritis.
Penicillin skin testing is needed for patients with a history of an immediate hypersensitivity reaction in whom a penicillin must be used. BPO-polylysine conjugate and penicillin G are used with histamine and saline as controls. The prick technique (see chapter in Merck on Allergic and Other Hypersensitivity Disorders: Specific tests) is used first. If the patient has a history of a severe explosive reaction, reagents should be diluted 100-fold for initial testing. If prick tests are negative, intradermal testing may follow. If skin tests are positive, treating patients with penicillin may induce an anaphylactic reaction. If tests are negative, a serious reaction is less likely but not excluded. Although the penicillin skin test has not induced de novo sensitivity in patients, patients should usually be tested only immediately before essential penicillin therapy is begun…” [2]
References
1. Centers for Disease Control and Prevention, Workowski KA, Berman SM. Management of patients who have a history of penicillin allergy. Sexually transmitted diseases treatment guidelines 2006. MMWR Morb Mortal Wkly Rep 2006 Aug 4;55(RR-11):33-5. (http://www.guideline.gov/summary/summary.aspx?doc_id=9677&nbr=5186&ss=6&xl=999).
2. Merck Manual. Drug hypersensitivity. Last revised November 2005. (http://www.merck.com/mmpe/sec13/ch165/ch165e.html).
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