Medscape: Not surprisingly, this study found that patients with reported penicillin allergy were much more likely to receive broad-spectrum antibiotics such as fluoroquinolones, clindamycin, vancomycin, and third-generation cephalosporins. These patients were also more likely to experience an allergic reaction to another agent while in the hospital. Given that the penicillin allergy itself is likely not representative of a true immunoglobulin (Ig)E-mediated response, why do these patients experience this higher rate of reported reactions to other agents?
Dr. Macy: There is a certain rate of adverse events that occur with all antibiotic use. Thus, more antibiotic use is associated with higher rates of various antibiotic "allergies." Most of these, however, are not IgE-mediated or reproducible upon rechallenge.
Dr. Solensky: Additionally, patients with a history of allergy to one antibiotic are more likely to react to another antibiotic, even if the reactions are not IgE-mediated. It is not known why patients who react to one antibiotic are more likely to react to another unrelated antibiotic. Presumably, they have a "promiscuous" immune system that likes to react against drugs. Also, there might be genetic predispositions, but evidence for this is very limited. The reactions to the drugs are not necessarily the same kind of reaction. For example, one reaction, such as to penicillin, could be immediate anaphylaxis after the first dose, whereas a reaction to a sulfonamide antibiotic could be a delayed-onset blistering rash.
Medscape: Most worrisome, this study documented a much higher incidence of a number of serious infections. Patients with a self-reported penicillin allergy were 30% more likely to have an infection due to VRE, 23% more likely to experience C difficile, and 14% more likely to have MRSA. While this higher incidence has been documented previously,[4] this study confirms that finding in a much larger and more diverse sample of patients. The paper theorized that VRE was a result of increased use of vancomycin, and the higher rate of C difficile the result of fluoroquinolones. The researchers were unable to point to a specific reason for the higher rate of MRSA. Can you address this a bit more?
Dr. Macy: This may be a result of more time in the hospital, but further research is needed.
Dr. Solensky: The higher incidence of VRE and C difficile makes sense, and I would concur that it is likely due to increased use of certain antibiotics such as quinolones. MRSA has not been linked to use of certain antibiotics, so I am also not sure what the reason is for this association. One possibility is more frequent or longer previous hospital stays/medical care, but I agree that more research is needed.
Medscape: This study documented that the hospital length of stay for a patient with a self-reported allergy was 0.59 days longer than for a patient without this history. The analysis of the cost implications of a self-reported penicillin allergy were specific to the institution in which the study was conducted and primarily based on the cost of that longer stay incurred in a single hospitalization. But the lifetime costs related to penicillin allergy could be anticipated to be much greater and related to other factors, such as use of more expensive medicine, in addition to the costs of an extra day in the hospital. Can the results be extrapolated to examine the costs of self-reported penicillin allergy in this broader context?
Dr. Macy: Because of the results of this study, we are interested to learn and could extrapolate that the lifetime costs of a penicillin allergy could be anticipated to be much greater.
Dr. Solensky: It is a certainty that if penicillin allergy is ruled out (via penicillin skin testing/challenge), the cost savings will extend and probably multiply well beyond the first hospitalization. This would be more difficult (but not impossible) to study because subsequent outpatient and inpatient encounters over years would need to be reviewed.
Medscape: The paper noted that < 0.1% of patients with reported penicillin allergy undergo confirmatory testing. Can you discuss some of the reasons behind this very low rate of testing and describe the current science around confirmation of penicillin allergy?
Dr. Macy: Physicians need to be proactive on this issue. This has not been on their radar. This is a case where not doing something, avoiding penicillins, causes a problem. The tests to determine true penicillin allergy are widely available, safe, and effective. A complete test does take about 2 hours, primarily because of the 1-hour observation after the oral amoxicillin challenge if the skin test results are negative.
Dr. Solensky: On the part of allergists, not enough emphasis has been placed on performing penicillin skin testing. Also, on the part of primary care doctors, not enough patients are referred to allergists for penicillin skin testing. Therefore, to correct this situation, both allergists and nonallergists need to be targeted.
Medscape: What about the issue of skin testing in an already hospitalized patient or in a critically ill patient? Is there ever justification for administering penicillin prior to testing? Are there patients who are too sick to test?
Dr. Solensky: Testing hospitalized patients is sometimes not feasible due to the logistics of having allergists available to perform testing in some medical centers. Because penicillin skin testing is very safe, patients being "too sick" would not be a reason not to test. Depending on the reaction history, rarely there might be scenarios in which cautious administration of penicillin might be appropriate without prior skin testing -- usually because of an emergent need for penicillin or unavailability of personnel to perform skin testing.
Medscape Pharmacists © 2014 WebMD, LLC
Cite this: Penicillin Allergy: A Mountain or a Molehill? - Medscape - Apr 30, 2014.
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