Risk of Neutropenia in Adults Treated with Piperacillin-Tazobactam or Cefazolin: A Retrospective Cohort Study.

Background: Neutropenia is an adverse effect associated with the use of several antibiotics, including piperacillin-tazobactam (P/T). Previous findings have suggested that the risk of neutropenia in children is significantly higher with P/T than with ticarcillin-clavulanate.

Objectives: To compare the risk of neutropenia associated with P/T and with cefazolin in an adult population and to describe the characteristics of neutropenia episodes observed.

Methods: This descriptive retrospective study involved patients aged 18 years or older who received a minimum of 10 days of treatment with P/T or cefazolin between January 2009 and December 2013. Patients who experienced neutropenia (absolute neutrophil count < 1.5 × 10⁹/L) were compared, using univariate and multivariate logistic regression models, between those who received P/T and those who received cefazolin.

Results: A total of 207 patients were included (104 who received P/T and 103 who received cefazolin). Ten episodes of neutropenia were observed, 5 with each antibiotic (4.8% and 4.9%, respectively; odds ratio 0.99, 95% confidence interval 0.278-3.527). The mean cumulative dose of piperacillin was 290.4 g among patients who experienced neutropenia and 247.0 g among all patients treated with P/T, and the mean treatment duration was 24.0 days and 21.0 days, respectively. The average time before the onset of neutropenia was slightly longer with P/T than with cefazolin (22.0 versus 17.2 days, p = 0.38).

Conclusions: Although these results require confirmation in a larger clinical trial (to lessen possible attribution bias), the risk of neutropenia appeared to be similar between P/T and cefazolin.