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 administ ration of ampicillin-sulbactam on group B streptococcal colonization a nd bacteremia in newborn rabbits. STUDY DESIGN: Before induction of la bor, limed pregnant New Zealand White rabbits on day 29 of a 31-day ge station received no therapy or ampicillin-sulbactam 50 mg/kg intramusc ularly as a single dose 2 to 8 hours before delivery, Labor was induce d with oxytocin. After delivery, the oropharynx of each pup was inocul ated 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 h eart at death or after 96 hours. Ampicillin-sulbactam concentrations w ere determined at delivery in both mothers and pups. RESULTS: Thirteen animals were assigned to no therapy and 14 animals to ampicillin-sulb actam. Untreated pups had 100% oropharyngeal colonization at 24 hours. Pups treated with antibiotic were significantly less likely to have p ositive 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 surviva l at 48 hours (89% vs 62%, p < 0.0001). When neonatal oropharyngeal co lonization at 24 hours after birth was compared with length of time fr om maternal antibiotic injection to delivery, there was a significant polynomial relationship (r = 0.78, p < 0.05). Ampicillin-sulbactam ser um concentrations were highest 3 to 5 hours after injection. An invers e relationship existed between the rate of neonatal oropharyngeal colo nization with group B streptococci at 24 hours after birth and neonata l ampicillin serum concentrations near birth (r = 0.733). CONCLUSION: Transplacental treatment with a single intramuscular dose of ampicilli n-sulbactam significantly decreased neonatal colonization and bacterem ia after oral inoculation with type la group B Streptococcus. An effec t of ampicillin-sulbactam was evident as early as 2 hours but maximal 3 to 5 hours after injection.