Double trouble: how big a problem is redundant anaerobic antibiotic coverage in Veterans Affairs medical centres?

To assess the prevalence of, and the variation in, avoidable use of metronidazole in the Veterans Affairs (VA) healthcare system Barcode Medication Administration (BCMA) data were retrospectively assessed for all patients hospitalized between January 2006 and December 2010 in acute-care wards of all VA medical centres (VAMCs) with complete BCMA data and at least 10 acute-care non-intensive care unit (ICU) beds. Potentially avoidable metronidazole days of therapy (DOT) were defined as the administration of metronidazole with another anti-anaerobic antibiotic on the same day for at least two consecutive days during the same hospitalization. Metronidazole was not considered redundant in combination with another anti-anaerobic agent within 28 days after a positive test for Clostridium difficile and during hospitalizations associated with discharge diagnosis codes for cholecystitis or cholangitis. A total of 128 VAMCs satisfied the inclusion criteria. Over the study period there were a total of 782,821 DOT of metronidazole (57.4 DOT per 1000 patient-days), of which 183,267 (23.4%) fulfilled the criteria for avoidable metronidazole DOT. The percentage of avoidable metronidazole DOT remained stable over the study period (22.8% in 2006 and 22.9% in 2010) despite a decrease in overall metronidazole use. There was wide variation in the percentage of avoidable metronidazole DOT among facilities (2010: median 20.3%, IQR 15.3%-29.4%). Piperacillin/tazobactam was the most commonly administered drug on avoidable metronidazole DOT (56.8%). Potentially avoidable use of metronidazole affected about a quarter of all days when metronidazole was given. The combination of metronidazole with piperacillin/tazobactam was particularly common and represents a possible target for antibiotic stewardship interventions.