AMPICILLIN FOR NEONATAL GROUP-B STREPTOCOCCAL PROPHYLAXIS - HOW RAPIDLY CAN BACTERICIDAL CONCENTRATIONS BE ACHIEVED

OBJECTIVE: Our purpose was to determine how rapidly bactericidal conce ntrations of ampicillin against group B streptococci are achieved in a mniotic fluid and cord blood after a 2 gm maternal infusion. STUDY DES IGN: Ampicillin was administered at varying time intervals between 3 a nd 67 minutes before elective cesarean delivery in 40 women. Samples o f amniotic fluid were obtained by amniocentesis just before the uterin e incision was made. Umbilical and maternal blood were obtained at the time of delivery. Ampicillin concentrations were measured by high-pre ssure liquid chromatography. RESULTS: The mean concentrations of ampic illin measured in maternal and umbilical cord sera all exceeded the mi nimum bactericidal concentrations reported for group B streptococci (0 .25 to 2.0 mu g/ml) and were achieved as soon as 5 minutes after ampic illin infusion, Similarly, bactericidal levels of ampicillin in the am niotic fluid could be detected as early as 5 minutes. However, such co ncentrations of ampicillin in the amniotic fluid were achieved in only 85% of the pregnancies studied. CONCLUSIONS: Bactericidal levels of a mpicillin against group B streptococci can usually he achieved rapidly in both fetal blood and amniotic fluid after a standard 2 gm intraven ous dose given to the mother for neonatal prophylaxis.