Prophylactic use of ampicillin and penicillin G in pregnant women has been shown to be effective in preventing vertical transmission of group B streptococcal infection. In pregnant women who are allergic to penicillin, clindamycin and erythromycin have been recommended as acceptable alternatives. However, in the past 10 years, severe neonatal infections have been reported, despite documented prophylaxis with clindamycin and erythromycin. Pearlman and colleagues conducted a study to determine the frequency of in vitro resistance of group B streptococci to these penicillin alternatives and to define ways of treating pregnant women who report penicillin allergy.

Clinical specimens of group B streptococci were obtained from genitourinary sites by cotton swab in 100 patients to assess in vitro rates of resistance to clindamycin, erythromycin, penicillin G, vancomycin and cefazolin. Labor and delivery records for all women who were screened for a history of penicillin allergy and who delivered at a university medical center during a four-month period were also collected.

All of the 100 clinical isolates of group B streptococci obtained were sensitive to penicillin G, cefazolin and vancomycin. Thirteen (16 percent) of the 82 isolates tested were resistant to erythromycin, and 15 percent were resistant to clindamycin. Resistance to more than one agent was also observed. Of the 13 erythromycin-resistant isolates, resistance to clindamycin was present in eight (62 percent), and nine out of the 10 clindamycin-resistant isolates (90 percent) were also resistant to erythromycin. Penicillin allergy was cited by 111 of the 963 women studied (12 percent). Of these, 14 reported severe reactions, 13 reported rashes, and six reported nausea or diarrhea. Seventy percent of the women who reported penicillin allergy had no specific observable manifestations during the study.

The authors conclude that the significant levels of resistance to clindamycin and erythromycin found in this study could explain the failure of current regimens to prevent group B streptococcal infection in pregnant women reporting penicillin allergies. The authors recommend more focused questioning when obtaining a history of penicillin allergies or using skin testing to verify reported penicillin allergy, since many women may be denied effective prophylaxis with penicillin because of their nebulous report of a previous adverse effect. For most patients in this study who reported penicillin allergies, an acute hypersensitivity reaction that contraindicated penicillin use could not be established.