Higher antibiotic dose for C-section prophylaxis in obese

1. Obese women who received 3 grams of cefazolin prior to cesarean delivery were more likely to achieve clinically effective drug levels than those who received 2 grams.

2. Higher BMI was correlated with lower likelihood of achieving the minimal inhibitory concentration.

Evidence Rating Level: 2 (Good)

Study Rundown: Cesarean (C-section) delivery is one of the greatest risk factors for postpartum infection, which includes endometritis and wound complications. Compared with women delivering vaginally, women undergoing cesarean delivery have a 5- to 20- fold greater likelihood of developing an infection. Risk for infection is further increased in patients who are obese such that up to a third of severely obese patients undergoing cesarean delivery experience wound complications. Another risk factor for postpartum infection is unplanned cesarean, or C-section performed in labor; obese women are at increased risk for unplanned cesarean due to their increased risk of labor dystocia, the most common indication for cesarean delivery in the United States. As the rates of Cesarean delivery and obesity continue to rise, it is critical to identify measures to minimize infection risk. Typically, a single dose of narrow spectrum antibiotic, such as cefazolin, is administered preoperatively. While antibiotic prophylaxis has demonstrated a significant reduction in postoperative infections, a prior study showed that minimal inhibitory concentrations (MIC) were not achieved in obese women with the standard 2 gram dose. Here authors evaluated whether a 3 gram (g) dose was more effective at inhibiting microbial growth and found that a greater proportion of obese women treated with a higher dose achieved the MIC.

Limitations included small sample size and use of a historical cohort for comparison. Future investigations might employ a larger sample population and assessment of both minimal inhibitory concentrations and rates of postpartum infections to identify the most appropriate dosage for antibiotic prophylaxis in obese women undergoing cesarean delivery.

Click to read the study in AJOG

Relevant Reading: Effects of maternal obesity on tissue concentrations of prophylactic cefazolin during cesarean delivery

In-Depth [prospective cohort]: This study evaluated the pharmacologic effects of using 3g of cefazolin as antibiotic prophylaxis in obese women undergoing Cesarean delivery at term (n = 28), compared with a historical cohort who received 2g (n = 29). Women were categorized as obese (body mass index [BMI] 30-39.9 kg/m²) or extremely obese (BMI >40 kg/m²). The MIC was defined as 8 µg/ml. Outcomes of interest were cefazolin concentration in serum and adipose tissue.

In the obese (BMI 30-40 kg/m²) subgroup, 100% of women receiving 3g achieved the MIC compared with only 20% of those who received 2g (p < 0.001). Among the extremely obese BMI >40 kg/m²) women, 71.4% achieved the MIC with 3g and 0% achieved the MIC with 2g. Overall, women with BMI ≥30 kg/m² were more than 8 times as likely to reach the MIC with the higher dose. Drug concentration was inversely related with BMI, with each unit increase in BMI associated with 18% decreased odds of attaining the MIC.

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