Does Keflex Cover Group B Strep?
No, Keflex (cephalexin) is NOT recommended for Group B Streptococcus coverage and should not be used for GBS prophylaxis or treatment. While cephalexin has some in vitro activity against GBS, it does not achieve adequate intraamniotic concentrations and is not included in CDC guidelines for GBS management 1.
Why Cephalexin Fails for GBS
The FDA label for Keflex does not list Streptococcus agalactiae (Group B Strep) among its indicated organisms 2. Although older research shows cephalexin has some activity against GBS in vitro with MICs of 2 to >16 mg/L 3, these concentrations are inadequate for clinical efficacy, particularly in the critical intrapartum setting where preventing neonatal transmission is paramount.
What Actually Works: CDC-Recommended Alternatives
For Non-Penicillin Allergic Patients:
- First-line: Penicillin G (5 million units IV, then 2.5-3.0 million units every 4 hours) OR Ampicillin (2g IV, then 1g every 4 hours) 1
For Penicillin-Allergic Patients WITHOUT High-Risk Features:
- Use Cefazolin (2g IV initial dose, then 1g every 8 hours until delivery) 1, 4
- Cefazolin is specifically recommended because pharmacologic data demonstrate it achieves effective intraamniotic concentrations 1
- Critical distinction: Cefazolin (a first-generation cephalosporin given IV) is appropriate; cephalexin (oral) is not
For Penicillin-Allergic Patients WITH High-Risk Features:
High-risk features include history of anaphylaxis, angioedema, respiratory distress, or urticaria following penicillin or cephalosporin administration 1.
- If GBS susceptible to clindamycin: Clindamycin 900mg IV every 8 hours 1
- If susceptibility unknown or resistant: Vancomycin 1g IV every 12 hours 1
Common Pitfalls to Avoid
Don't confuse cephalexin with cefazolin: These are different drugs with different pharmacokinetics. Only cefazolin achieves adequate intraamniotic levels 1
Don't use oral antibiotics for intrapartum prophylaxis: GBS prophylaxis requires IV administration to achieve rapid, adequate tissue concentrations 4
Verify the allergy history: Women reporting "penicillin allergy" without true anaphylactic features can safely receive cefazolin. Studies show over 55% of such patients inappropriately receive vancomycin or clindamycin when cefazolin would be appropriate 5
Check susceptibility when using clindamycin: Increasing resistance to clindamycin and erythromycin has been documented, with some studies showing 25% erythromycin resistance and 13% clindamycin resistance 6, 7. Always perform susceptibility testing when possible for high-risk allergic patients 1
The Bottom Line
Cephalexin has no role in GBS management. For penicillin-allergic patients without anaphylaxis risk, use cefazolin IV, not cephalexin. The distinction matters because inadequate GBS prophylaxis directly impacts neonatal morbidity and mortality from early-onset sepsis.