![]() ![]() Further complicating this issue is the fact that some beta-lactams (namely amino-penicillins like amoxicillin) cause an idiopathic, non-IgE-mediated rash in up to 10% of patients. It is also worth noting that it has been shown that patients with a penicillin allergy are more likely to react to any drug (including structurally unrelated compounds) as compared with those who do not report a penicillin allergy. cefazolin, cephalexin) carrying a higher risk of cross-reaction than those of later generations (e.g. Recent studies have failed to reproduce this incidence and have concluded that cross-reactivity between penicillins and cephalosporins is more likely between 0% and 10%, with first generation cephalosporins (e.g. Early reports of cross-reaction (up to 41.7%) have been attributed to contamination of early cephalosporins with trace penicillin derivatives. The actual cross-sensitivity between penicillins and cephalosporins is considered much lower than originally proposed when cephalosporins were first marketed in the 1960s. As you described, this will inevitably lead to worse patient outcomes and potential colonization with resistant organisms. When we eliminate all beta-lactams from our arsenal we are left with sub-optimal drugs with larger side effect profiles and broader antimicrobial spectrums. Penicillins, despite being some of our oldest antibiotics, remain some of our most effective, bactericidal options. Self-reported penicillin allergies have become a huge problem in light of the looming antibiotic crisis stemming from our increasing rates of antibiotic resistance and lack of new antibiotics in the pipeline. Thank you for bringing attention to this important topic. If the patient is being admitted to the hospital, consider inpatient testing for IgE mediated hypersensitivity as this has been shown to decrease both inpatient complications and cost of care. In one prevalence study, only 6% of patients reporting penicillin allergy were referred for allergy testing. For patients deemed unsafe to attempt alternative beta-lactam treatment, start a non-beta-lactam and refer for allergy testing. If it is deemed that a patient has an allergy description that is not consistent with an IgE mediated allergy, it is likely safe to attempt use of another beta-lactam such as a cephalosporin. Lastly, asking the patient what antibiotics they tolerated in the past (i.e amoxicillin or other beta-lactams) may help you assess for true penicillin allergy. It is also useful to know if the patient had to previously seek emergency department care for an allergy as this indicates a more serious reaction. A rash is usually IgG mediated and not concerning while hives, angioedema or anaphylaxis are consistent with a true IgE mediated allergy. When obtaining a history, it is important to ask about a patient’s previous reaction to penicillin. In most settings a good clinical history of allergy symptoms can appropriately guide antibiotic choice. Emergency Department Approach to Patients with a Self-Reported Penicillin Allergy More recent studies demonstrate cephalosporin-penicillin cross-allergenicity rates between 0.1% and 2%, carbapenem-penicillin cross-allergenicity rates less than 1% and aztreonam-penicillin cross-allergenicity rates 0%. Furthermore, cross-allergenicity rates are much less common than originally thought. Using these numbers we can extrapolate that only 1/100 patients have a true allergy to penicillin. We know that of patients who report a penicillin allergy, 90% are able to tolerate penicillin. This leads back to our original question, “Are you really allergic to penicillin?” While this may seem inconsequential, recent data suggest patients with reported penicillin allergies have increased hospital length of stay and increased risks of clostridium difficile, vancomycin resistant enterococcus, and MRSA infections. Penicillin allergy is the most commonly reported allergy in the United States with a prevalence of up to 12.8% of the population. Right now you are thinking, “Are you really allergic to penicillin?” and “What’s the worst that could happen if you do get a penicillin?” Prevalence of Penicillin Allergy However, your electronic medical record (EMR) immediately shows a “pop-up” indicating this patient has a penicillin allergy. You diagnose a non-purulent cellulitis and place an order for cefazolin. A 50-year-old woman presents to your emergency department with a chief complaint of pain and swelling in her left leg. ![]()
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