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38: Perinatal pharmacokinetics of azithromycin for cesarean prophylaxis

      Objective

      Extended spectrum cesarean prophylaxis at cord clamp with cefazolin and azithromycin (AZI), which covers Ureaplasma spp, decreases post-cesarean infections. A clinical trial is underway to determine if addition of AZI to cefazolin prior to incision reduces surgical site infections. This study sought to evaluate the perinatal pharmacokinetics of AZI following a single pre-incision dose.

      Study Design

      30 women undergoing cesarean delivery were randomized to receive 500 mg of AZI IV initiated 15, 30, or 60 minutes prior to incision. Maternal plasma samples were drawn up to 8 hrs after the dose. Amniotic fluid (AF) and cord blood (CB) were collected at delivery. AZI and its added internal standard clarithromycin were extracted using a protein precipitation method. Analyte separation and detection were performed using high performance liquid chromatography and tandem mass spectrometry. The assay was linear from 2.5-5,000 ng/mL in a 50 μL sample. Plasma pharmacokinetic parameters were estimated using noncompartmental analysis.

      Results

      The mean (SD) plasma area under the concentration-time curve (AUC0-∞), maximum concentration (Cmax), and minimum concentration (Cmin) were 6030 (2170) ng*h/mL, 4500 (2430) ng/mL, and 147 (43) ng/mL, respectively. Plasma Cmax was reached within 1 hr and was over 2X the in vitro minimum inhibitory concentration (500-1000 ng/mL) of most Ureaplasma spp. The concentrations were sustained with a half-life of 6.2 hrs. The median AF concentration was 33 ng/mL at a median of 0.92 hrs post-dose. The median CB concentration was 152 ng/mL at a median of 0.95 hrs post-dose.

      Conclusion

      A single dose of AZI achieves effective and sustained maternal plasma concentrations, is rapidly transported across the placenta, and is detectable in both AF and CB. The transplacental transport indicates maternal treatment with AZI has the potential to reduce perinatal infections caused by Ureaplasma spp. Additional studies are underway quantifying AZI in adipose and myometrium to further define the role of AZI in cesarean prophylaxis.
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      Maternal plasma, cord blood, and amniotic fluid AZI concentrations following a single pre-incision dose