Introduction

Both the timing and selection of antimicrobial prophylaxis (AP) reduce the risk of surgical site infections (SSI), but the logistics around varied infusion times are often overlooked. ^{Reference de Jonge, Gans and Atema1} National AP guidelines jointly issued in 2013 by the American Society of Health-System Pharmacists (ASHP), the Infectious Diseases Society of America, the Surgical Infection Society, and the Society for Healthcare Epidemiology of America recommend that AP should be infused (both initiated and completed) within a 60 min window before incision. ^{Reference Bratzler, Dellinger and Olsen2} However, this recommendation is based primarily on studies focused on first- and second-generation cephalosporins infused via rapid intravenous (IV) push over a number of minutes by an anesthesiologist prior to skin incision. Vancomycin and fluoroquinolones are well known exceptions and are permitted a longer 120 min infusion window, due to rate limitations precluding the ability to completely administer doses in the shorter time frame. Subsequent studies have validated the consequences of failing to adhere to this earlier window for vancomycin, noting increased SSI rates when infusions are initiated too close to the time of incision and describing the significant resource allocation required to coordinate the complex logistics of an operating room setting. ^{Reference Borja, Sharma and Amendolia3,Reference Malhotra, Piazza and Demoor4} Despite the need for slow IV drip administration and a long half-life with active metabolites promoting adequate tissue concentrations for prolonged periods of time, metronidazole (MTZ) has not been clearly specified in this guideline carve-out, and one prior study has noted challenges with completing MTZ infusions prior to skin incision when given as a 30 min infusion by anesthesia in the operating room. ^{Reference Danan, Smith and Kruer5}

MTZ IV infusion is only commercially supplied as a diluted and neutralized 500 mg/100 mL solution, as the undiluted reconstituted product is not appropriate for direct IV injection due to its low pH. In the United States, it is indicated for use as preoperative AP in patients undergoing elective colorectal surgery (COLO) at a dose of 15 mg/kg (approximately 1 g for a 70 kg patient) infused over 30 – 60 min and completed approximately 1 hour prior to incision, followed by intraoperative re-dosing every 6 hours with 7.5 mg/kg (i.e., ∼500 mg). ⁶ Alternatively, the 2013 ASHP guidelines suggest an initial MTZ dose of 500 mg preoperatively within 60 min without any intraoperative re-dosing. ^{Reference Bratzler, Dellinger and Olsen2} While institutional practices vary, published evidence to support the safety of infusions over less than 15 – 30 min is sparse. ^{Reference Dellinger7}

Although other AP options exist that provide the spectrum of activity required for procedures entering the gastrointestinal tract, the combination of cefazolin and MTZ is preferred by our institution, a 600-bed academic medical center, given studies suggesting lower rates of SSI when compared to cephamycins ⁶ and the unnecessary additional spectrum of ertapenem. Longitudinal quality and performance improvement efforts around COLO SSI at our institution are coordinated via a multidisciplinary coalition comprising key stakeholders in Hospital Epidemiology and Infection Prevention, Colorectal Surgery, Perioperative Nursing, Anesthesiology, Antimicrobial Stewardship, and Pharmacy. As part of our investigation into opportunities for improvement with respect to AP, we noted that MTZ initiation was frequently documented to be given by anesthesia within just minutes of, or even after, incision in the operating room. Herein, we report the results of a focused intervention to optimize timing of preoperative COLO AP, with a focus on MTZ.