To perform a graded challenge first give 1/100th or 1/10th of a typical dose, then increase by a factor of 10 until the entire dose is given. Instead, it is hoped that any cross-allergenicity will be mild if a small dose of the allergen is given. This is why patients allergic to ceftazidime may also be allergic to aztreonam the side chains are similar.Ī graded challenge does not affect a patient’s immune response to a potential allergen. Side chains rather than the beta-lactam ring may be responsible for cross-allergenicity. Even if a skin test is negative, cross-allergenicity may still occur due to similar side-chains. If this is done major and minor penicillin determinants must be used. I can not remember ever using skin testing to evaluate a patient’s penicillin allergy. For example, if I am considering using a carbapenem in a patient with a rash to penicillin I ask “Is it acceptable to take a less than 1% chance of causing a rash in this patient?” Of if I am considering using a cephalosporin in a patient with anaphylaxis to penicillin I ask “Is it acceptable to take a 2% chance of anaphylaxis in this patient?” Framing the question like this makes it easy to decide whether the risk is acceptable or if an alternative antibiotic is preferred. What other antibiotics can you take without a problem?Īfter I determine whether the allergy is true and whether it is likely IgG or IgE mediated, I ask myself a patient-specific question. How was the reaction treated? Reactions that were treated with an ED visit or hospitalization are more worrisome for being IgE-mediated.Ĥ. What exactly was the reaction? Whole-body rashes imply an IgG-mediated reaction, while hives, anaphylaxis, and angioedema imply IgE-mediated.ģ. How long ago did the reaction occur? B-cell memory fades, so a childhood reaction in an elderly patient is often not significant.Ģ. When evaluating a patient with a reported penicillin allergy, I will first try and determine whether the patient has an allergy and if so is it IgG or IgE-mediated? Here are the four questions I will typically ask:ġ. A patient’s reaction will never switch from an IgG-mediated to an IgE-mediated reaction, but an IgE-mediated reaction may manifest the first time as hives and the next time as anaphylaxis. IgE-mediated reactions such as hives, angioedema, and anaphylaxis are often severe. IgG-mediated reactions such as rash are never life-threatening. The risk of cross-allergenicity may not be clinically significant, depending on the type of reaction. The actual rates of cross-allergenicity are far less.Ĭephalosporin-penicillin cross-allergenicity rates are somewhere between 0.1% and 2%.Ĭarbapenem-penicillin cross-allergenicity rates are less than 1%.Īztreonam-penicillin cross-allergenicity rates are 0%. Many clinicians quote a cross-allergenicity rate between penicillins and cephalosporins as 10%. Presumably, this is because second-line non-beta-lactam antibiotics are used when penicillins are avoided.Ĭross-allergenicity rates are much less than what you may have learned in training. difficile, MRSA, and VRE infections are higher in patients who report a penicillin allergy. Patients that report penicillin allergy on hospital admission have longer lengths of stay and more complications than patients without a reported penicillin allergy. In fact, the number of patients who report a penicillin allergy but can tolerate penicillin may be as high as 90%. Most patients who report a penicillin allergy don’t have one. With recent warnings on non-beta-lactam antibiotic classes such as fluoroquinolones, the importance of determining what beta-lactam antibiotics a patient with a penicillin allergy can safely tolerate has never been greater. The penicillin allergy dance is one that replays itself over and over on a daily basis. If you have the book, please head over to Amazon to leave a quick review. Good advice on how to be most effective as a pharmacist responding to emergencies, especially for newer pharmacists or those new to rapid response teams. This is a great resource for new hospital pharmacists students and residents. One anonymous customer wrote: Very practical. The reviews are essential for helping a potential reader decide if the book is for them. Subscribe on iTunes, Android, or StitcherĪ big shout-out to those of you that took a moment to leave a review of my book A Pharmacist’s Guide to Inpatient Medical Emergencies on Amazon. In this episode, I’ll discuss penicillin allergy and cross-reactivity.
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