CHICAGO--Can patients with a vague history of penicillin allergy be given the drug safely? Doing so could avoid the need to administer broad-spectrum antibiotics, thereby decreasing the risk of antimicrobial resistance.

Two new studies shed light on this issue. One suggests that a high proportion of patients with penicillin-specific immunoglobulin E (IgE) antibodies do have a vague history of penicillin allergy.[1] However, the other suggests that penicillin sensitivity may decrease over time; thus, most such patients can be given the antibiotic without fear of a severe reaction.[2] Both studies recommend using skin testing to identify those patients who are currently allergic to penicillin—rather than relying on past allergy histories—when considering treatment with an antimicrobial agent.

The problem is far from trivial. A third new study suggests that the incidence of penicillin allergy may be higher in hospital patients than in the general population.[3] However, the study authors also found that documentation of penicillin allergy is often inadequate, making it difficult for physicians to select antibiotics wisely. It, too, recommends skin testing to identify those who can be given penicillin safely.

CLARIFYING A VAGUE HISTORY

A history of penicillin allergy is unreliable in predicting which patients will suffer immediate allergic reactions following subsequent administration of the drug, an analysis of data from 30 studies indicates.[1]

Roland Solensky, MD, et al compared penicillin skin test results from patients with a convincing history of penicillin allergy with those from patients with a vague history. A patient's history was considered convincing if there existed evidence of an IgE-mediated reaction, such as anaphylaxis, angioedema/urticaria, pruritic rash, or bronchospasm; the history was considered vague if the symptoms were unlikely to be IgE mediated (eg, maculopapular rash, gastrointestinal upset, or unknown reactions).

Among the individual studies, the percentage of skin test-positive patients who had only a vague history of penicillin allergy ranged from 0% to 70%. The researchers reported that the wide variation was likely due to differences in patient selection, the length of time elapsed since the reaction occurred, the skin testing techniques, and the methods of skin test interpretation. However, when the studies were taken together, Solensky and colleagues found that one third of the patients who had tested positive on the skin test had only a vague history of penicillin allergy.

The overall patient sample approximates an ideal population of "all comers" with a variety of penicillin allergy histories, the researchers believe. They, therefore, recommended that each and every patient with a history of penicillin allergy should be given a skin test before penicillin is administered.

PENICILLIN SENSITIVITY MAY DECREASE OVER TIME

If not all patients who have positive skin test results have a convincing history of penicillin allergy, should physicians assume that all patients with vague histories have true penicillin allergies? Not necessarily, the second study suggests.

"Most patients with histories of allergy to penicillin have negative reactions to skin tests and may receive penicillin safely," say Mercedes E. Arroliga, MD, et al.[2] Their conclusion is based on the findings of a prospective pilot study of all patients with histories of penicillin allergy who were admitted to the medical intensive care unit of the Cleveland Clinic Foundation, in Ohio, between April 1 and June 30, 1999.

A total of 24 patients were enrolled in the study. Three patients had had recent episodes of an immediate reaction to penicillin, including anaphylaxis. Among the remaining 21 patients, who had a history of skin rash, urticaria, or unknown characteristics, 20 had a negative reaction to a penicillin skin test, the researchers reported. Treatment with a penicillin antibiotic was started in 10 patients, and there were no significant side effects.

Penicillin skin testing can provide an accurate determination of current penicillin hypersensitivity, Arroliga et al concluded. It may also reduce the overall number of patients requiring broad-spectrum antibiotics.

A SECOND LOOK AT MEDICAL RECORDS

Both the Solensky and Arroliga studies suggest that histories of penicillin allergy should not be taken at face value without further investigation. This is also the conclusion of a third study. "Often, patients are labeled as allergic to penicillin in their medical record without an in-depth investigation as to the nature of their reaction," commented Collin E. Lee, RPh, and colleagues,[3] who conducted a retrospective review of antimicrobial usage patterns at Northwestern Memorial Hospital, in Chicago, over a two-month period in 1998.

About one quarter of the 1,893 patients who required antimicrobial therapy reported an allergy to at least one agent (in most cases, penicillin), and a surprisingly high number— 85 —reported allergies to two or more agents. However, only 4% of the 601 antimicrobial allergies reported had been documented (by description of the specific reaction) on the hospital admission or antibiotic order form.

Vancomycin, the researchers found, was the agent prescribed most often for patients reporting antimicrobial allergies. About 40% of the patients who reported an allergy to penicillin and/or a cephalosporin were given vancomycin; in contrast, about 17% of the patients who did not report having antimicrobial allergies received that drug.

Notably, 30 patients who had reported a penicillin allergy were treated with a ß-lactam antimicrobial. Only one of these patients had an adverse reaction, Lee and his associates reported, and the reaction was not life threatening. "Health care professionals should carefully assess subjective claims of penicillin allergy before choosing alternative antimicrobial therapy," these researchers said, adding that the overuse of alternative antimicrobial agents "will adversely impact the ability to manage emerging antimicrobial resistance."

--Shauna Kubose

References
1. Solensky R, Earl HS, Gruchalla RS. Penicillin allergy: prevalence of vague history in skin test-positive patients. Ann Allergy Asthma Immunol. 2000;85:195-199.

2. Arroliga ME, Wagner W, Bobek MB, et al. A pilot study of penicillin skin testing in patients with a history of penicillin allergy admitted to a medical ICU. Chest. 2000;118:1106-1108.

3. Lee CE, Zembower TR, Fotis MA, et al. The incidence of antimicrobial allergies in hospitalized patients: implications regarding prescribing patterns and emerging bacterial resistance. Arch Intern Med. 2000;160:2819-2822.