What is the treatment for Haemophilus influenzae and Streptococcus Group B infections?

Treatment for Haemophilus influenzae and Streptococcus Group B Infections

For Haemophilus influenzae infections, use ampicillin or amoxicillin-clavulanate as first-line therapy (accounting for β-lactamase production), while for Group B Streptococcus infections, ampicillin or penicillin G are the preferred agents, with ceftriaxone or cefotaxime as alternatives.

Haemophilus influenzae Treatment

Community-Acquired Respiratory Infections

Outpatient Management:

• First-line: Amoxicillin-clavulanate is preferred due to increasing β-lactamase-producing strains 1

  • Adults: Co-amoxiclav 625 mg three times daily orally for 7 days 1
  • Children <12 years: Co-amoxiclav (amoxicillin component 90 mg/kg/day in 2 divided doses) 1
  • Children ≥12 years: Doxycycline 200 mg loading dose, then 100 mg once daily as alternative 1

• Alternative regimens (for penicillin allergy): Macrolides (clarithromycin 500 mg twice daily or azithromycin) or respiratory fluoroquinolones 1

Important caveat: While ampicillin historically was first-line, β-lactamase production among H. influenzae is increasing significantly, making amoxicillin-clavulanate more reliable 1, 2. However, in areas with documented low β-lactamase prevalence, ampicillin alone remains acceptable 1.

Hospitalized Patients

Medical ward:

• Second-generation cephalosporin (cefuroxime 750-1500 mg IV every 8 hours) OR third-generation cephalosporin (ceftriaxone 1 g IV daily or cefotaxime 1 g IV every 8 hours) 1
• For fully immunized patients in areas with minimal penicillin resistance: Ampicillin or penicillin G acceptable 1

ICU/Severe infections:

• Anti-pseudomonal β-lactam (cefepime, piperacillin-tazobactam) PLUS ciprofloxacin or levofloxacin if risk factors for Pseudomonas present 1
• Standard severe CAP: β-lactam plus macrolide or respiratory fluoroquinolone 1

Meningitis

• Neonates and infants: Ampicillin 150-200 mg/kg/day IV in divided doses every 3-4 hours 3
  • Specific neonatal dosing based on gestational and postnatal age 3
• Children and adults: Ceftriaxone 1-2 g IV daily or cefotaxime 1, 4
• Critical consideration: Avoid ampicillin-chloramphenicol combination due to documented antagonism 5

Group B Streptococcus Treatment

Invasive Infections (Septicemia, Meningitis)

First-line therapy:

• Ampicillin is the drug of choice 3
  • Adults: 150-200 mg/kg/day IV in divided doses every 3-4 hours 3
  • Neonates: Dosing based on gestational and postnatal age:
    • ≤34 weeks gestation, ≤7 days postnatal: 100 mg/kg/day IV every 12 hours 3
    • ≤34 weeks gestation, 8-28 days postnatal: 150 mg/kg/day IV every 12 hours 3

    • 34 weeks gestation: 150 mg/kg/day IV every 8 hours 3

Alternative therapy:

• Ceftriaxone or cefotaxime for penicillin-allergic patients 1, 4
• Penicillin G (benzyl penicillin) 1-4 million units IV every 2-4 hours 1

Critical warning: Do NOT use ampicillin-chloramphenicol combination for Group B Streptococcus meningitis—in vitro studies demonstrate antagonism with inhibition of ampicillin's bactericidal activity 5.

Respiratory Tract Infections

• Ampicillin 250-500 mg every 6 hours for adults weighing >40 kg 3
• Children <40 kg: 25-50 mg/kg/day in divided doses every 6-8 hours 3

Duration of Therapy

• Minimum 48-72 hours beyond clinical improvement or bacterial eradication 3
• Minimum 10 days for Group A β-hemolytic streptococci to prevent rheumatic fever/glomerulonephritis 3
• Meningitis: Continue IV therapy for at least 3 days, then may transition to IM route 3
• Shorter courses (5-7 days) acceptable for uncomplicated pneumonia with adequate clinical response 1

Key Clinical Pitfalls

Resistance patterns to monitor:

• H. influenzae: Increasing β-lactamase production (up to 25% in some regions), widespread trimethoprim-sulfamethoxazole resistance 2, 6
• Avoid macrolides as monotherapy for H. influenzae—poor coverage 1, 7
• Cephalexin, cefaclor, and loracarbef have inadequate activity against H. influenzae (only 20% susceptibility) 1

Drug interactions:

• Never combine ampicillin with chloramphenicol for streptococcal infections including Group B Streptococcus 5

Antimicrobial stewardship:

• Amoxicillin (without clavulanate) remains highly effective for S. pneumoniae co-infections 2
• Consider local resistance patterns when selecting empiric therapy 1