Antibiotic Prophylaxis for GBS‑Positive Pregnant Women with High‑Risk Penicillin Allergy (Urticaria)

Risk Stratification

Hives (urticaria) after penicillin exposure classify a pregnant patient as high‑risk for anaphylaxis; CDC guidelines state that high‑risk patients must not receive penicillin, ampicillin, or cefazolin for intrapartum GBS prophylaxis【1】.
Low‑risk penicillin allergies (e.g., isolated rash, itching, nausea without urticaria) may safely receive cefazolin 2 g IV loading then 1 g IV q8 h【1】, whereas high‑risk allergies (including urticaria) require alternative non‑β‑lactam agents【1】.

If the prenatal GBS isolate is susceptible to both clindamycin and erythromycin, the recommended regimen is clindamycin 900 mg IV q8 h until delivery【1】.
If the isolate is susceptible to clindamycin but resistant to erythromycin, clindamycin may be used only when the D‑zone test for inducible clindamycin resistance is negative; otherwise, vancomycin 1 g IV q12 h should be given【1】.
If the isolate is resistant to clindamycin or shows inducible clindamycin resistance, the guideline advises vancomycin 1 g IV q12 h until delivery【1】.

In the absence of susceptibility results, vancomycin 1 g IV q12 h until delivery is the preferred default agent, especially when labor begins before testing can be completed【1】.

Cefazolin must not be used in patients with urticaria because the reaction is IgE‑mediated and poses a high risk of cross‑reactivity with cephalosporins; the CDC explicitly recommends against cefazolin in this group【1】.
Erythromycin is no longer acceptable for GBS prophylaxis in high‑risk penicillin‑allergic patients【9】.

Antibiotics should be administered at least 4 hours before delivery to achieve optimal intra‑amniotic concentrations; both vancomycin and clindamycin meet this target when given ≥4 h prior to birth【11】.

These recommendations are based on high‑quality CDC guidelines (2010), which received a strong recommendation rating and were endorsed by the American Academy of Pediatrics (2011)【11】.
The algorithm remained unchanged in the 2019‑2020 updates, with only minor modifications to the timing of GBS screening【1】.