Ampicillin for neonatal group B streptococcal prophylaxis: how rapidly can bactericidal concentrations be achieved?
OBJECTIVE
Our purpose was to determine how rapidly bactericidal concentrations of ampicillin against group B streptococci are achieved in amniotic fluid and cord blood after a 2 gm maternal infusion.


METHODS
Ampicillin was administered at varying time intervals between 3 and 67 minutes before elective cesarean delivery in 40 women. Samples of amniotic fluid were obtained by amniocentesis just before the uterine incision was made. Umbilical and maternal blood were obtained at the time of delivery. Ampicillin concentrations were measured by high-pressure liquid chromatography.


RESULTS
The mean concentrations of ampicillin measured in maternal and umbilical cord sera all exceeded the minimum bactericidal concentrations reported for group B streptococci (0.25 to 2.0 micrograms/ml) and were achieved as soon as 5 minutes after ampicillin infusion. Similarly, bactericidal levels of ampicillin in the amniotic fluid could be detected as early as 5 minutes. However, such concentrations of ampicillin in the amniotic fluid were achieved in only 85% of the pregnancies studied.


CONCLUSIONS
Bactericidal levels of ampicillin against group B streptococci can usually be achieved rapidly in both fetal blood and amniotic fluid after a standard 2 gm intravenous dose given to the mother for neonatal prophylaxis.
Bloom
S L
SL
Department of Obstetrics and Gynecology, University of Texas Southwestern Medical Center, Dallas 75235-9032, USA.
Cox
S M
SM
Bawdon
R E
RE
Gilstrap
L C
LC
D000653:Amniotic Fluid / Q000378:metabolism; D000667:Ampicillin / Q000493:pharmacokinetics / Q000627:therapeutic use*; D002585:Cesarean Section; D002851:Chromatography, High Pressure Liquid; D005260:Female; D005312:Fetal Blood / Q000378:metabolism; D006801:Humans; D007231:Infant, Newborn; D007232:Infant, Newborn, Diseases / Q000517:prevention & control*; D009994:Osmolar Concentration; D010406:Penicillins / Q000493:pharmacokinetics / Q000627:therapeutic use*; D011247:Pregnancy; D013290:Streptococcal Infections / Q000517:prevention & control*; D013292:Streptococcus agalactiae / Q000187:drug effects; D013997:Time Factors
D010406:Penicillins; D000667:Ampicillin