ORLANDO -- Concomitant IV use of vancomycin and piperacillin/tazobactam, regardless of extended or traditional infusion, appeared to result in acute kidney injury in roughly one out of every five inpatients, researchers reported here.

Among 226 adult inpatients, no cases of nephrotoxicity were found among those treated with vancomycin alone, but 22.7% of those treated with a traditional infusion of concomitant vancomycin and piperacillin/tazobactam, as well as 19.6% of those given an extended infusion of the combination, experienced elevated creatinine levels to the point of toxicity (P<0.05), Ramadas Balasubramanian, PharmD, PhD, of the Carolinas Medical Center-Pineville in Charlotte, N.C., and colleagues reported at the midyear meeting of the American Society of Health-System Pharmacists.

Recent studies have suggested that concomitant use of vancomycin and piperacillin/tazobactam may increase the risk of kidney injury. Previous studies have also suggested that IV vancomycin doses greater than 4 g per day increase the risk of a patient developing kidney toxicity.

For this study, Balasubramanian and colleagues looked 226 adult inpatients who had been treated with vancomycin, piperacillin/tazobactam, or a combination of the two from November 2009 to February 2013 at their 210-bed hospital.

As baseline, all of the patients had serum creatinine (SCr) levels lower than 1 mg/dL. Kidney toxicity was defined as an increase in SCr of at least 0.5 mg/dL.

Among the patients treated for infection:

• 45 received an IV of vancomycin only; average dose 1.91 g (range 0.83-3.63)
• 46 were treated with 30 minutes of a traditional infusion (TI) of piperacillin/tazobacta, average dose 10.34 g (range 6.75-14.4)
• 45 were treated with 4 hours of an extended infusion (EI) of piperacillin/tazobactam, average dose 9.75 g (range 3.38-13.5)
• 44 were treated with 30 minutes of a traditional infusion (TI) of a combination of vancomycin (1.98 g on average) and piperacillin/tazobactam (11.02 g on average)
• 46 were treated with 4 hours of an extended infusion (EI) of a combination of vancomycin (2.07 g on average) and piperacillin/tazobactam (10.75 g on average)

Nephrotoxicity did not occur in any of the patients treated with vancomycin alone. But, 4.4% of patients on piperacillin/tazobactam TI and 2.2% of those on piperacillin/tazobactam EI reached the point of kidney injury.

Far worse than piperacillin/tazobactam alone in either infusion method were vancomycin/piperacillin/tazobactam combinations, as 22.7% of TI and 19.6% of EI patients given those combinations reached nephrotoxicity (P<0.05).

From this retrospective analysis, Balasubramanian and colleagues concluded that the concomitant use of vancomycin and piperacillin/tazobactam, regardless of infusion method, resulted in high rates of kidney toxicity.