REFERENCES
We’re not following guidelines on GBS prophylaxis in penicillin allergy
Matheson KA, Lievense SP, Catanzaro B, Phipps MG. Intrapartum group B streptococci prophylaxis in patients reporting a penicillin allergy. Obstet Gynecol. 2008;111:356–364.
In this study, conducted at a single institution (Brown University), Matheson and colleagues sought to assess the adequacy of prophylaxis for GBS infection in women who had an allergy to penicillin. Specifically, the authors sought to determine how well practitioners at their institution adhered to the 2002 Centers for Disease Control and Prevention (CDC) guidelines, which specify that cefazolin should be used for prophylaxis in patients who are penicillin-allergic but not at high risk for anaphylaxis.1 For patients at high risk for anaphylaxis, clindamycin may be used for prophylaxis if the organism is known to be susceptible. If susceptibility has not been documented, vancomycin should be administered.1
Overall, 95% of GBS-positive, penicillin-allergic patients received prophylaxis (95% CI, 91–97). However, only 15% of these women received appropriate prophylaxis as defined by the CDC (95% CI, 11–12). Clindamycin was administered to 83% of patients, but susceptibility testing was performed in only 11%. At the time of this study, 26% of all GBS isolates at Brown were resistant to clindamycin; 37% were resistant to erythromycin.
The authors concluded that adherence to CDC guidelines was clearly less than optimal. Even at 1 year after adoption of the guidelines, only 20% of patients received appropriate prophylaxis.
Type of allergic reaction is key to selection of prophylactic agent
GBS is uniformly sensitive to penicillin and ampicillin. It also is 100% sensitive to cefazolin, the preferred drug for intrapartum prophylaxis in penicillin-allergic women who have a low risk of anaphylactic reaction to penicillin.
FIGURE 2 Group B streptococcus
A clear zone of hemolysis on blood agar is a key characteristic of group B streptococcus.However, it probably is better to avoid cephalosporins in patients who report a previous anaphylactic reaction to penicillin or ampicillin, even though the risk of cross-reactivity between penicillin and cephalosporin is low. In such patients, possible alternatives include erythromycin, clindamycin, and vancomycin.
Erythromycin is no longer recommended
At the University of Florida, we reported that 21% of GBS strains were resistant to erythromycin.2 At Brown University, Matheson and colleagues reported that 37% of GBS isolates were resistant to erythromycin. On the basis of similar reports, the CDC has concluded that erythromycin no longer should be used for GBS prophylaxis.
At our institution, we also have noted a disturbing trend of increased GBS resistance to clindamycin. In our recent report, 9% of GBS strains were resistant to this antibiotic. Similarly, Matheson and coworkers observed that 26% of GBS isolates in their center were resistant to clindamycin.
Neonatal GBS infection is now one of the leading causes for malpractice suits in obstetrics. Key issues presented in these suits include:
- failure to screen
- failure to use the correct culture medium for screening
- failure to obtain test results in a timely manner
- failure to use the correct drug for prophylaxis.
In GBS-positive patients, practitioners should inquire about penicillin allergy and document the exact type of reaction experienced by the patient, if it is accurately known. If the reported reaction to penicillin was not life-threatening, patients should receive cefazolin, 2 g IV initially, then 1 g every 8 hours until delivery. If the reaction to penicillin was immediate and life-threatening, the patient should receive clindamycin, 900 mg IV every 8 hours, if the organism is confirmed to be susceptible. Susceptibility testing should be documented in the medical record.
If such testing is unavailable, vancomycin is the drug of choice.
Susceptibility testing is vital in penicillin-allergic women
Because of observations such as these, the CDC now recommends that clindamycin be used for GBS prophylaxis only if antimicrobial susceptibility tests have confirmed that the organism is sensitive. If susceptibility testing cannot easily be performed, practitioners should use intravenous (IV) vancomycin, 1 g every 12 hours, for prophylaxis. Potential side effects of vancomycin include allergic reactions, gastrointestinal irritation, ototoxicity, and nephrotoxicity. The latter two effects are extremely unlikely in patients who receive only one or two IV doses of the drug.
20% to 30% of gravidas are colonized with GBS
GBS is one of the two major causes of pneumonia, meningitis, and sepsis in both pre-term and term newborns. Approximately 20% to 30% of women are colonized with the organism at some point during pregnancy. Universal screening for GBS at 35 to 37 weeks’ gestation, combined with intrapartum antibiotic prophylaxis, has been highly effective in reducing the frequency of invasive GBS infection.