What is the recommended dose and duration of ampicillin (Ampicillin) for treating Group B strep urinary tract infection?

Treatment of Group B Streptococcus Urinary Tract Infection with Ampicillin

For uncomplicated Group B Streptococcal urinary tract infections, ampicillin should be administered at a dose of 500 mg orally every 8 hours for 3-7 days. 1

Dosing Recommendations

Adults:

• Oral ampicillin: 500 mg every 8 hours for uncomplicated UTI 1
• For complicated UTIs or severe infections: 18-30 g/day IV in divided doses 1
• Alternative oral option: Amoxicillin 500 mg every 8 hours 1

Children:

• Ampicillin 150-400 mg/kg/day IV in 4 divided doses (maximum 12,000 mg/day) 1
• For neonates and young infants, dosing depends on gestational and postnatal age 1:
  • Gestational age >34 weeks, postnatal age ≤7 days: 50 mg/kg/dose IV every 12 hours 1
  • Gestational age >34 weeks, postnatal age >7 days: 75 mg/kg/dose IV every 12 hours 1
  • For older infants: 50 mg/kg/dose IV every 8 hours 1

Duration of Therapy

• Uncomplicated UTI: 3-7 days 1
• Complicated UTI: 5-7 days 1
• Severe infections or bacteremia: 10-14 days 1

Clinical Considerations

Efficacy

• Ampicillin has demonstrated good efficacy against Group B Streptococcus (GBS) in urinary tract infections 2
• Peroral treatment with ampicillin typically proceeds successfully for GBS UTIs 2
• Single-dose therapy (3g for adults, 100 mg/kg for children) may be effective for uncomplicated cases, but standard multi-day regimens are more commonly recommended 3

Special Populations

• For pregnant women with GBS UTI, treatment is essential as GBS can cause chorioamnionitis and endometritis 4
• For patients with penicillin allergies, alternative agents should be selected based on susceptibility testing 1

Monitoring and Follow-up

• Urine culture should be obtained before initiating therapy to confirm the diagnosis and guide treatment 1
• Significant bacteriuria is defined as ≥50,000 CFUs/mL of a single urinary pathogen 1
• Follow-up cultures may be indicated if symptoms persist despite appropriate therapy 2

Potential Pitfalls and Caveats

• Development of resistance may occur with prolonged therapy; consider rotational therapy with other antibiotics if extended treatment is needed 5
• High-dose ampicillin has been associated with seizures in neonates, so caution is warranted when using high doses 6
• For complicated or recurrent infections, evaluation for structural abnormalities of the urinary tract may be indicated 1
• Distinguishing between colonization and true infection is important to avoid unnecessary treatment 1

Alternative Treatments

• For patients with penicillin allergies or treatment failures, consider:
  • Nitrofurantoin 100 mg orally four times daily for uncomplicated UTI 1
  • Fosfomycin 3 g orally as a single dose for uncomplicated UTI 1
  • For complicated infections, consult infectious disease specialists for alternative regimens 1

Remember that ampicillin remains the drug of choice for GBS urinary tract infections when the organism is susceptible 2, 5.