The effect of timing of single-dose transplacental ampicillin-sulbactam therapy for prevention of neonatal group B streptococcal colonization and bacteremia in a rabbit model.
OBJECTIVE
Our purpose was to evaluate the effect of maternal administration of ampicillin-sulbactam on group B streptococcal colonization and bacteremia in newborn rabbits.


METHODS
Before induction of labor, timed pregnant New Zealand White rabbits on day 29 of a 31-day gestation received no therapy or ampicillin-sulbactam 50 mg/kg intramuscularly as a single dose 2 to 8 hours before delivery. Labor was induced with oxytocin. After delivery, the oropharynx of each pup was inoculated with 10(9) cfu of type la group B Streptococcus. Cultures of each pup were taken from the oropharynx and anorectum daily and from the heart at death or after 96 hours. Ampicillin-sulbactam concentrations were determined at delivery in both mothers and pups.


RESULTS
Thirteen animals were assigned to no therapy and 14 animals to ampicillin-sulbactam. Untreated pups had 100% oropharyngeal colonization at 24 hours. Pups treated with antibiotic were significantly less likely to have positive oropharyngeal cultures at 24 and 48 hours after birth than did untreated pups (24 hours 47% vs 100%, p < 0.0001; 48 hours 68% vs 91%, p = 0.0006). For anorectal cultures treated pups were significantly less likely to have positive culture results. Heart cultures were also less likely to have positive results for treated animals at 48 and 72 hours than for untreated animals (48 hours 30% vs 96%, p = 0.0001; 72 hours 31% vs 71%, p = 0.03). Treated pups had higher rates of survival at 48 hours (89% vs 62%, p < 0.0001). When neonatal oropharyngeal colonization at 24 hours after birth was compared with length of time from maternal antibiotic injection to delivery, there was a significant polynomial relationship (r = 0.78, p < 0.05). Ampicillin-sulbactam serum concentrations were highest 3 to 5 hours after injection. An inverse relationship existed between the rate of neonatal oropharyngeal colonization with group B streptococci at 24 hours after birth and neonatal ampicillin serum concentrations near birth (r = 0.733).


CONCLUSIONS
Transplacental treatment with a single intramuscular dose of ampicillin-sulbactam significantly decreased neonatal colonization and bacteremia after oral inoculation with type la group B Streptococcus. An effect of ampicillin-sulbactam was evident as early as 2 hours but maximal 3 to 5 hours after injection.
McDuffie
R S
RS
Department of Obstetrics and Gynecology, Kaiser Permanente, Denver, Colorado, USA.
Blanton
S J
SJ
Charland
S L
SL
Gibbs
R S
RS
D000667:Ampicillin / Q000008:administration & dosage* / Q000627:therapeutic use; D000818:Animals; D000831:Animals, Newborn / Q000382:microbiology; D016470:Bacteremia / Q000382:microbiology / Q000517:prevention & control*; D004195:Disease Models, Animal; D004359:Drug Therapy, Combination / Q000008:administration & dosage / Q000627:therapeutic use; D005260:Female; D009960:Oropharynx / Q000382:microbiology; D011247:Pregnancy; D011817:Rabbits; D013290:Streptococcal Infections / Q000382:microbiology / Q000517:prevention & control*; D013292:Streptococcus agalactiae / Q000302:isolation & purification; D013407:Sulbactam / Q000008:administration & dosage* / Q000627:therapeutic use; D013997:Time Factors
D000667:Ampicillin; D013407:Sulbactam