What is the recommended antibiotic treatment for group B streptococcus (GBS) bacteremia?

Antibiotic Treatment for Group B Streptococcus Bacteremia

Penicillin G is the preferred first-line antibiotic for GBS bacteremia, administered as 5 million units IV initially, followed by 2.5-3.0 million units IV every 4 hours, due to its narrow spectrum, universal GBS susceptibility, and proven efficacy. 1, 2

First-Line Treatment

• Penicillin G remains the gold standard because all GBS isolates worldwide remain universally susceptible to penicillin with no documented resistance 2
• The dosing regimen of 5 million units IV loading dose followed by 2.5-3.0 million units IV every 4 hours achieves adequate drug levels while avoiding neurotoxicity 1
• Ampicillin is an acceptable alternative (2 g IV initial dose, then 1 g IV every 4 hours), though it has broader spectrum activity than penicillin G 1, 2
• High doses of penicillin are specifically recommended for serious GBS infections because of somewhat higher minimal inhibitory concentrations compared to other streptococci 3

Treatment for Penicillin-Allergic Patients

Non-Severe Allergy (No History of Anaphylaxis, Angioedema, Respiratory Distress, or Urticaria)

• Cefazolin is the preferred alternative: 2 g IV initially, then 1 g IV every 8 hours 1, 4
• Cross-reactivity between penicillins and cephalosporins occurs in approximately 10% of penicillin-allergic patients, making risk stratification essential 2, 4

High-Risk Allergy (History of Anaphylaxis, Angioedema, Respiratory Distress, or Urticaria)

• Susceptibility testing is mandatory for clindamycin and erythromycin before selecting an alternative agent 1, 2
• If susceptible to both clindamycin and erythromycin: Use clindamycin 900 mg IV every 8 hours 1, 4
• If clindamycin-susceptible but erythromycin-resistant: Test for inducible clindamycin resistance; if negative, clindamycin may be used 5, 1
• If resistant to clindamycin or susceptibility unknown: Use vancomycin 1 g IV every 12 hours 1, 4
• Resistance rates are significant: approximately 21% of GBS isolates show erythromycin resistance and 4% show clindamycin resistance 6

Special Considerations for Bacteremia

• Surgical management may be required in addition to parenteral antibiotics, particularly for soft-tissue or bone infections associated with bacteremia 3
• Mortality from invasive GBS disease is particularly high in elderly patients and those with underlying conditions such as diabetes mellitus, malignant neoplasms, and liver disease 3
• Nosocomial infection and polymicrobial bacteremia occur in a significant proportion of patients with invasive GBS disease 3

Critical Pitfalls to Avoid

• Do not use vancomycin as first-line therapy unless no other options exist, to minimize promoting antimicrobial resistance 2
• Do not underdose penicillin G—the higher doses (2.5-3.0 million units every 4 hours) are necessary for serious infections due to higher MICs 3
• Do not skip susceptibility testing in penicillin-allergic patients at high risk for anaphylaxis, as resistance to second-line agents (erythromycin, clindamycin) continues to rise globally 7
• Verify allergy history carefully, as many reported penicillin allergies are not true IgE-mediated reactions, and patients may be candidates for penicillin or cefazolin rather than less effective alternatives 4