4. “If I test positive for GBS, how and when will you treat me?”
The current ACOG guidelines recommend that all colonized women be treated intrapartum with prophylactic antibiotics regardless of whether risk factors are present. Treatment should be started at the time of admission and continued until the infant is delivered.5
The drugs of choice for intrapartum prophylaxis are intravenous penicillin or ampicillin. If the patient has a mild allergy to penicillin, cefazolin is the appropriate alternative. If the patient has a severe allergy to penicillin, the 2 options are vancomycin or clindamycin. If the latter drug is used, the laboratory must perform sensitivity testing because 13% to 20% of strains of GBS may be resistant to clindamycin. The frequency of resistance to erythromycin now ranges from 25% to 32%. Thus, erythromycin is no longer used for intrapartum prophylaxis.5-7,9
The appropriate intravenous dosages of these antibiotics are listed in the TABLE.5 The new ACOG guidelines have revised the previous recommendations for dosing of penicillin, eliminating the 2.5 million-unit dose. They also have revised the dosing recommendations for vancomyin, eliminating the previous recommendation of 1 g every 12 hours.5 The new recommendations regarding vancomycin are particularly important and are based, at least in part, on an interesting report from Onwuchuruba and colleagues.10 These authors studied maternal and cord blood concentrations of vancomycin in mother-infant dyads receiving either the original recommended dosage of vancomycin (1 g every 12 hours) or a dosage of 15 to 20 mg/kg every 8 hours. With standard dosing, only 9% of neonates had therapeutic vancomycin serum concentrations at delivery. With the 20 mg/kg dose of vancomycin, the percent of neonates with therapeutic serum concentrations of vancomycin increased to 80%.
5. “For how long must I be treated in labor before my baby will be protected by the antibiotics?”
The current ACOG Committee Opinion stresses the importance of treating the colonized mother for at least 4 hours prior to delivery.5 This recommendation is based primarily on the landmark report by De Cueto and colleagues.11 These authors evaluated colonized women who received intrapartum prophylaxis at varying times prior to delivery. Their primary endpoint was the percentage of newborns who were colonized with GBS. If the mothers had received antibiotics for less than 1 hour prior to delivery, 46% of neonates were colonized. This figure was equal to the rate of colonization in neonates whose mothers received no antibiotics. When the interval was 1 to 2 hours, the percentage was 29%. When mothers had received antibiotics for 2 to 4 hours, the neonatal colonization rate fell to 2.9%. When antibiotics had been administered for greater than 4 hours, the rate of neonatal colonization was only 1.2%.
Fairlie and colleagues recently reported the results of another interesting investigation comparing the effectiveness of prophylaxis based on duration of treatment and choice of individual antibiotics.12 Prophylaxis with penicillin or ampicillin for 4 hours or more was 91% effective in preventing early-onset neonatal infection in term infants and 86% effective in preventing infection in preterm infants. These outcomes were superior to the outcomes in both term and preterm infants who received penicillin or ampicillin for less than 4 hours.
These observations agree with the findings of McNanley and colleagues who evaluated vaginal colony counts of GBS following different periods of antibiotic administration.13 These authors noted that mean colony counts decreased 5-fold within 2 hours of penicillin administration, 50-fold within 4 hours, and 1,000-fold within 6 hours.
Despite these compelling findings, the ACOG Committee Opinion stresses that obstetric interventions such as amniotomy and oxytocin augmentation should not be delayed simply to permit a certain time period of antibiotic administration.5
Continue to: “If I were to have a scheduled CD before the onset of labor and/or ruptured membranes, would I still need to receive antibiotics?”...