1300 - ACOG Committee Opinion #797 and the Dose of Intrapartum Vancomycin: a Potential Danger to Mother and Newborn Alike

Background: Intra-partum (IP) IV vancomycin (VAN) 20 mg/kg every 8 hours is proposed by #797 for the prevention of early onset neonatal group B streptococcal disease (GBS), a recommendation for which the basis of scientific merit is poor. The goal of our study was to analyze the sparsely sampled published data and raise awareness about the underlying risk of VAN toxicity with this dosing approach.

Methods: Plasma and cord-blood concentration-time data of IV VAN given to mothers in the IP period was analyzed. 5000 Monte Carlo runs were conducted to simulate maternal/fetal exposure (AUC_{0-24; 24-48}) for doses of 1500, 1750 and 2000 mgs q8h and for possible birth times at two-hour intervals. Neonatal VAN clearance was not possible to determine; hence, we used a validated PK model to calculate exposure for the first 24h of life for gestational ages (GA) of 33 to 40 weeks. The AUC range of 400 – 600, and > 600 mg*h/L were considered for indices of efficacy and toxicity, respectively.

Results: Estimates from 30 pairs of serum and cord-blood concentrations analyzed with a 2-compartment model are shown in Table 1. Maternal VAN exposures seem acceptable up to 2 IP doses given with mean (SD) AUC_0-24 of 394 (140), 474 (167), and 540 (193) mg*h/L for the 1500, 1750 and 2000 mg regimens. Most mothers (up to 83%) who receive three or more doses will be subjected to nephrotoxic exposures (Figure 1.).  Neonatal evaluations indicate similarly low PTAs for the three dosing regimens when the efficacy target is considered (Figure 2. A). On the other hand, the PTAs for potentially nephrotoxic exposure is expected to reach undesirable levels when three or more doses were to be administered. The risk is profoundly high in GA of 33 to 35 weeks and birth times beyond 20 hours after the initiation of intra-partum prophylaxis (Figure 2. B).Figure 1.
Figure 2.A
Figure 2.B


Conclusion: Current recommendations by #797 for dosing of vancomycin pose significant risk to mother and newborn alike, especially in cases with lengthy duration of labor. Based on our results, maternal therapeutic drug monitoring for all cases requiring more than two doses should be considered. With the proposed dosing regimen going un-adjusted, 1 out of 4 newborns and 4 out of 5 mothers may be subjected to nephrotoxic exposures in prolonged labor.Table 1.