Piperacillin-Tazobactam Allergies: An Exception to Usual Penicillin Allergy

Purpose: The majority of penicillin allergy labels are false, and skin tests (ST) have high negative predictive value (NPV) of up to 90%. Piperacillin-tazobactam (PT) allergy has been suspected to be an exception to this, but existing literature is scarce. We investigate the epidemiology, clinical characteristics, testing outcomes and predictive value of ST in patients referred for suspected PT allergies. Methods: The records of all patients referred for suspected PT allergy testing and prescription rates of PT in all Hong Kong public hospitals (2015-2019) were analyzed. Results: There was an increase in both PT prescriptions and number of newly reported PT allergies between 2015 and 2019. The majority (91.1%) of patients with suspected PT allergy had at least 1 underlying medical co-morbidity or immunosuppressant use leading to increased risk of infections. Thirty-six patients with suspected PT allergy completed ST. Two patients had positive ST, and 32/34 patients with negative ST underwent drug provocation testing (DPT). Nine of these patients were diagnosed with PT allergy based on positive DPT. Overall, 11/34 (32.4%) were diagnosed with PT allergy and the NPV of ST was 71.9%. Conclusions: There is growing utilization of PT and corresponding cases of suspected allergies. The majority of suspected PT allergies had increased risk for recurrent infections. Unlike other penicillin allergy, there is a high rate of genuine PT allergy (up to 30%) and a poor NPV of ST (up to 70%). DPT remains the gold standard for accurate diagnosis, and all patients with a suspected allergy should undergo thorough allergy workup.