What is the most appropriate perioperative dosing for intravenous (IV) cefazolin (Ancef) as prophylaxis in a 46-year-old male with a body mass index (BMI) of 50 kg/m2 and normal laboratory test results, undergoing a 3-hour short surgical repair procedure for an open fracture of the left foot?

From the Guidelines

The most appropriate perioperative dosing for intravenous cefazolin as prophylaxis for MK would be a 2-g infusion over 30 minutes once. This recommendation takes into account MK's BMI of 50 kg/m², which classifies him as morbidly obese. For surgical prophylaxis in obese patients, higher initial doses of cefazolin are recommended to achieve adequate tissue concentrations at the surgical site, as suggested by the principles outlined in the study by Hong and colleagues 1. The 2-g dose is appropriate for this patient with normal renal function, as indicated by his normal lab results. The single dose is sufficient for this relatively short 3-hour procedure, as cefazolin has a half-life that provides adequate coverage during this timeframe. While MK has a slightly elevated temperature (101°F), suggesting possible infection at the open fracture site, the standard prophylactic dose is still appropriate as the primary goal is to prevent surgical site infection during the repair procedure.

Some key points to consider in this scenario include:

• The importance of achieving adequate tissue concentrations of cefazolin at the surgical site, particularly in obese patients like MK, to prevent surgical site infections.
• The recommendation for higher initial doses of cefazolin in obese patients, as supported by the principles outlined in the study by Hong and colleagues 1.
• The sufficiency of a single 2-g dose for a short procedure like the one planned for MK, given the half-life of cefazolin and the patient's normal renal function.
• The need to balance the benefits of prophylactic antimicrobials with the potential risks of extended use, such as hypersensitivity reactions, renal failure, antimicrobial resistance, and Clostridium difficile-associated diarrhea, as discussed in the study by Hong and colleagues 1.

It's also worth noting that the 2014 practice guidelines for the diagnosis and management of skin and soft tissue infections by the Infectious Diseases Society of America recommend cefazolin dosing of 0.5–1 g every 8 h IV for surgical prophylaxis 1, but these guidelines do not specifically address the needs of morbidly obese patients like MK. Therefore, the recommendation for a 2-g infusion over 30 minutes once is based on more recent and relevant principles outlined in the study by Hong and colleagues 1.

From the FDA Drug Label

To prevent postoperative infection in contaminated or potentially contaminated surgery, recommended doses are: 1 gram IV or IM administered 1/2 hour to 1 hour prior to the start of surgery. For lengthy operative procedures (e.g., 2 hours or more), 500 mg to 1 gram IV or IM during surgery (administration modified depending on the duration of the operative procedure). The most appropriate perioperative dosing for intravenous (IV) cefazolin as prophylaxis in MK is 1 gram IV administered 1/2 hour to 1 hour prior to the start of surgery, and since the surgical repair procedure is planned to be 3 hours, an additional dose of 500 mg to 1 gram IV may be administered during surgery. 2

From the Research

Perioperative Dosing for Intravenous Cefazolin

To determine the most appropriate perioperative dosing for intravenous (IV) cefazolin as prophylaxis in MK, a 46-year-old male with an open fracture of his left foot and a BMI of 50 kg/m2, we need to consider the available evidence.

• The study by Gregoire and colleagues is not directly provided, but based on the information given, we can look at other studies for guidance.
• A study from 2022 3 analyzed both outcome and pharmacokinetic studies to determine the appropriate cefazolin dose in obese surgical patients. The study found that a 2-g dose of cefazolin is sufficient for surgery lasting up to 4 hours.
• Another study from 2024 4 evaluated the concentration and pharmacokinetics of intravenously delivered cefazolin at an open fracture site after surgical debridement. The study found that current prophylactic cefazolin dosing regimens result in successful antibiotic delivery to the traumatized limb in moderately severe open fractures.
• A study from 2022 5 determined the adequacy of an institutional standard dosing practice for infection prophylaxis in open cardiac surgery in patients heavier than 120 kg undergoing cardiopulmonary bypass. The study found that the studied dosing regimen met or exceeded targeted cefazolin concentrations for all study patients.

Recommended Dosing

Based on the available evidence, the most appropriate perioperative dosing for intravenous (IV) cefazolin as prophylaxis in MK would be:

• A 2-g infusion over 30 min once, as this dose has been shown to be sufficient for surgery lasting up to 4 hours 3.
• Alternatively, a 1-g loading dose over 30 min followed by 3 g by continuous infusion over 3 hrs could be considered, but there is less evidence to support this dosing regimen.
• The other options, a 4-g infusion over 30 min once and a 6-g continuous infusion over 3 hrs, are not supported by the available evidence.