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Penicillin, Cephalosporin Allergy Seldom Confirmed
Chicago -- Skin testing is essential before considering antibiotic substitution in patients who say they are allergic to penicillin or cephalosporins, investigators agreed at the annual meeting of the American College of Allergy, Asthma, and Immunology.
Such testing can reduce by up to 90% the number of patients who unnecessarily receive vancomycin, the researchers reported. That's because many patients claim to have histories of penicillin or cephalosporin allergies, but skin tests show that only a small percentage actually are reactive to these antibiotics.
The issue has major implications for patient care, since many Physicians automatically default to vancomycin when a patient's chart indicates history of penicillin or cephalosporin allergy With vancomycin resistance on the rise, reflexive prescription of this antibiotic--the last defense against many pathogens--is a bad habit.
"Allergy testing had a huge impact" in a study reported by Dr. James Li of the Mayo Clinic, Rochester, Minn. He and his colleagues reviewed charts from 62,796 medical and surgical admissions at two Mayo-owned hospitals for the year of 1998. The sample included 31,952 nonsurgical and 30,844 medical admissions, with a t2% overlap between the two, due to in-hospital transfers.
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Overall, 5,699 charts (9% of the total) indicated histories of allergy to penicillin, cephalosporin, or both. Penicillin allergy--real or imagined--was the most common, with 5,434 charts indicating this sensitivity.
The Mayo researchers skin tested a 150-patient subcohort of patients who reported antibiotic allergy histories and were about to undergo orthopedic surgery; 10% of these patients were skin test positive and required vancomycin substitution.
The other 90% of the patients were able to go without vancomycin, Dr. Li reported.
Dr. Kenneth Pinna of the Rush Medical Center--Cook County Hospital, Chicago, made a similar observation in a study of 32 patients seen in a community hospital in Reading, Pa., over an 8-month period from 1998 to 1999. All patients--12 men and 20 women--reported histories of systemic or localized allergic reactions to [beta]-lactam antibiotics and had been treated with vancomycin in the past.
Dr. Pinna skin tested these patients with a range of major and minor antibiotic allergens, including penicilloyl polylysine, penicillin G, penicilloate, and cefazolin. Skin testing for [beta]-lactam antibiotic allergy is accurate in the 90%-95% range, he said.
Four patients had positive skin tests; all were women, and three of the four had histories of systemic reactions to penicillin. But 25 patients had negative responses to all allergens, and 3 patients were anergic.
"True allergy prevalence is low in patients labeled 'penicillin-allergic,' and most vancomycin substitution is unnecessary," Dr. Pinna said. "I am advocating that these 'allergies' should be evaluated by someone qualified to determine whether a [beta]-lactam antibiotic would be safe enough, before going directly to vancomycin."
Skin testing also is underutilized in office-based practice.
Dr. Thomas Puchner, a Milwaukee internist, surveyed 378 primary care physicians (including pediatricians) and allergists, using a series of five clinical case scenarios of patients with histories variously suggestive of antibiotic allergy.
"They only skin test when there's a reported history of sepsis, and even then, only about 40% of the primary care doctors skin test," Dr. Puchner said. Overall, allergists were the most likely to test before antibiotic substitution, while community-based pediatricians were the least likely.
Skin testing can have a profound effect on vancomycin use, said Dr. Christine Radojicic, an allergy / immunology fellow at the Cleveland Clinic Foundation.
She reviewed 100 consecutive penicillin allergy skin tests performed at the Cleveland Clinic's inpatient service. Of these, only five tests were positive.
Of the 100 cases, Dr. Radojicic had some follow-up information on 57. Five patients had died of causes not related to antibiotics in the interval between skin testing and follow-up; she was able to reach 46 of the 52 remaining patients for an extensive phone interview regarding their subsequent experience with antibiotics.
Forty-one of these 46 patients--all of whom probably would have gotten vancomycin in the absence of skin testing--were able to take penicillin or cephalosporin without adverse effects. The other five refused to take penicillin-based antibiotics despite the negative skin test.
"You really need to explain skin testing and the meaning of skin test results to patients and their families. They need to understand the dangers of vancomycin overuse, and that when a skin test is negative, it means they are not allergic and that penicillin is safe," she said.
And hospital staff must remember to remove the "penicillin allergy alert" stickers from a patient's chart if the skin test proves negative, Dr. Radojicic added. In the Cleveland Clinic Study, 37% of the charts of patients with negative skin tests still carried the "alert" tag.