Daily gentamicin using ideal body weight demonstrates lower risk of postpartum endometritis and increased chance of successful outcome compared with traditional 8-hour dosing for the treatment of intrapartum chorioamnionitis

Background: Clinical chorioamnionitis complicates approximately 1-4% of pregnancies overall. Although universal agreement does not exist regarding the antibiotic regimen of choice, most studies have evaluated intravenous ampicillin dosed at 2 g every 6 hours plus gentamicin dosed every 8 hours. Only three studies have examined daily gentamicin for the treatment of intrapartum chorioamnionitis and thus is insufficiently investigated. Objective: This study seeks to determine whether daily dosing of gentamicin using ideal body weight for the treatment of intrapartum chorioamnionitis is more or equivalently efficacious when compared to traditional 8-hour dosing regimens. Materials and methods: We conducted a retrospective cohort study and reviewed charts on all women receiving treatment for intrapartum chorioamnionitis, which included intravenous gentamicin daily dosing calculated using 5 mg/kg ideal body weight or receiving traditional every 8 hours dosing of gentamicin at two large academic centers. Our primary outcomes were resolution of infection following delivery without the development of maternal endometritis and/or neonatal sepsis. Baseline characteristics were compared between dosing groups using Welch two-sample t-tests for continuous variables, uncorrected X-2 test and exact binomial 95% confidence intervals. We calculated the risk ratios of each outcome in the ideal versus traditional dosing groups using modified Poisson regression, both crude and adjusted. Adjusted models were controlled for variables determined to be potential confounders, which included BMI, diabetes mellitus, gestational blood pressure >140/90, group beta-Streptococcus status, race, advanced maternal age (>34 y), and parity. Results: The study included 500 patients with 255 patients receiving daily dosing of gentamicin and 245 receiving traditional dosing of gentamicin. Of the patients receiving daily gentamicin compared to traditional dosing, 95.7% (95% CI 94.9-96.6%) achieved the primary outcome versus 92% (95% CI 90.8 - 93.2%), 2.4% (95% CI 1.8-3%) developed endometritis versus 5.6% (4.5-6.7%), 1.6% (95% CI 1.1-2.1%) delivered neonates with sepsis versus 3.3% (CI 2.5-4.1%), and 36.9% required cesarean delivery versus 41.4%. In crude analysis, compared to traditional dosing, IDW daily dosing was associated with a lower risk of postpartum endometritis (RR 0.42, 95% CI 0.16-1.10, p = .032). After adjusting for BMI, diabetes mellitus, gestational blood pressure >140/90, group beta-Streptococcus status, race, advanced maternal age (>34 y), and parity, the IDW daily dosing group had a 5% greater chance of successful outcome (RR 1.05, 95% CI 1.00-1.10, p = .046) and a 64% lower risk of endometritis (RR 0.35, 95% CI 0.15-0.83, p = .017). Conclusion: Daily dosing of gentamicin using ideal body weight is associated with a lower risk of postpartum endometritis and high chance of a successful outcome in the treatment of intrapartum chorioamnionitis compared with traditional 8-hour dosing in our ethnically diverse, urban population and thus may be considered a superior option to every 8 hours dosing regimens.