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The Dreaded Penicillin Allergy

On arrival to CCU, the knowledgeable medical resident assessed a patient at high-risk of infection post emergency bowel resection and the decision to continue a short course of antibiotics post-op was made. Unfortunately, the patient had a documented penicillin allergy and there was some debate as to which antibiotics to use. A suggestion put forward was to switch the medication order from metronidazole/cefazolin to metronidazole/ciprofloxacin. The coverage of ciprofloxacin for common skin pathogens such as the Streptococcus spp. and Staphylococcus aureus could have been suboptimal. This was true for some of the common Enterobacteriaceae ssp. associated with post procedure infection. Given the recommended alternatives form Bugs and Drugs for severe penicillin allergies (gentamicin/ metronidazole or gentamicin/clindamycin) and the patient’s eGFR of 36ml/min, some investigation was warranted. After reviewing the chart history, it was discovered the patient received:

Ceftriaxone 1g IV and metronidazole 500mg IV at 08:30 March 16, 2106

Cefazolin 1g IV and metronidazole 500mg IV at 02:00 March 17, 2016

The patient had also tolerate imipenem in hospital on a previous visit.

During the patient interview, she described the allergy as a rash to her arms, chest and abdomen that had emerged within 24hrs of penicillin use in 2006.

On exam, the patient had no signs of rash on her chest, abdomen, back or legs. Given the alternatives, if antibiotic therapy were to continue, the suggested was made that cefazolin 1g IV and metronidazole 500mg IV be continued tid as ordered with careful monitoring for signs of an allergic reaction. The probability of cross reactivity between penicillins and cephalosporins was communicated to the residents, nurses and dispensary pharmacist. Needless to say, I was diligent to monitor closely for signs of an allergic reaction!

This served as a good lesson of where reviewing the patient medication history and a careful allergy assessment was beneficial in ensuring the patient received the most effective and safe medication. It was also an opportunity to demonstrate the utility of a pharmacist as part of the patient care team. A medical resident and a pharmacy resident may have a different approaches to the same problem however by working as a team we were able to determine the most viable option for the patient.

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