Duration of intrapartum prophylaxis and concentration of penicillin G in fetal serum at delivery.

Abstract

OBJECTIVE:

Intrapartum penicillin G prophylaxis aims to prevent early-onset group B streptococci (GBS) sepsis by interrupting vertical transmission. We examined the relationship between duration of prophylaxis and fetal serum penicillin G levels among fetuses exposed to fewer than 4 hours of prophylaxis compared with longer durations.

METHODS:

In this prospective cohort study, 98 laboring GBS-positive women carrying singleton gestations at 37 weeks or greater were administered 5 million units of intravenous penicillin G followed by 2.5 million units every 4 hours until delivery. Umbilical cord blood samples were collected at delivery, and penicillin G levels were measured by high-performance liquid chromatography. Intraassay and interassay coefficients of variation were less than 3%.

RESULTS:

Fetuses exposed to fewer than 4 hours of prophylaxis had higher penicillin G levels than those exposed to greater than 4 hours (P=.003). In multivariable linear regression analysis, fetal penicillin G levels were determined by duration of exposure, time since last dose, dosage, and number of doses, but not maternal body mass index. Penicillin G levels increased linearly until 1 hour (R(2)=.40) and then decreased rapidly according to a power-decay model (R(2)=.67). All subgroups analyzed were above the minimal inhibitory concentration (MIC) for GBS (0.1 micrograms/mL)(P<.002). Individual samples were 10-179-fold above the MIC. In patients receiving maintenance dosing, penicillin G did not accumulate in the cord blood and returned to baseline after each 4-hour interval.

CONCLUSION:

Short durations of prophylaxis achieved levels significantly above the MIC, suggesting a benefit even in precipitous labors. The designation of infants exposed to fewer than 4 hours of prophylaxis as particularly at risk for GBS sepsis may be pharmacokinetically inaccurate.

• Authors: Emma L Barber, Guomao Zhao, Irina A Buhimschi, Jessica L Illuzzi
• Journal: Obstetrics and gynecology (Obstet Gynecol) Vol. 112 Issue 2 Pt 1 Pg. 265-70 (Aug 2008) ISSN: 0029-7844 [Print] United States
• PMID: 18669721 (Publication Type: Journal Article, Research Support, N.I.H., Extramural)

Chemical References

• Penicillin G

Topics

• Adult
• Antibiotic Prophylaxis (methods)
• Female
• Fetal Blood (chemistry)
• Fetus (physiology)
• Humans
• Linear Models
• Penicillin G (administration & dosage, blood, pharmacokinetics)
• Prospective Studies
• Streptococcal Infections (blood, prevention & control)
• Streptococcus agalactiae