Treatment Duration for Group B Streptococcus Urinary Tract Infection with Ampicillin
For Group B Streptococcus (GBS) urinary tract infection, treat with ampicillin for 7 days for uncomplicated cystitis, or 7-14 days if the patient has complicated features such as pyelonephritis, bacteremia, or structural urinary tract abnormalities. 1
Standard Treatment Duration
A 7-day course of ampicillin is appropriate for uncomplicated GBS cystitis in non-pregnant patients, consistent with general UTI treatment guidelines that recommend 5-7 days for lower urinary tract infections 2, 1
Extend treatment to 7-10 days for complicated UTI or if the patient has risk factors such as diabetes, immunosuppression, or anatomic abnormalities 2
For GBS bacteremia associated with urinary source, treat for 7-10 days total once source control has been addressed, as recent high-quality evidence demonstrates that 7-day courses are non-inferior to 14-day courses for uncomplicated bacteremia 2, 3, 4
GBS-Specific Considerations
GBS remains highly susceptible to ampicillin (96% susceptibility), making it an excellent first-line choice when this organism is identified 5
Ampicillin 50 mg/kg IV every 6 hours (or 500 mg oral four times daily) is the standard dosing regimen for GBS infections 2, 6
GBS shows significant resistance to tetracyclines (72-82%) and co-trimoxazole (69%), so ampicillin or other beta-lactams should be strongly preferred 7, 5
Special Population: Pregnancy
Pregnant women with GBS bacteriuria require treatment at diagnosis AND intrapartum prophylaxis during labor, as any concentration of GBS in urine during pregnancy indicates heavy genital tract colonization 1, 8
Treat pregnant women with GBS UTI for 7-14 days using ampicillin or a cephalosporin, with the longer duration preferred to ensure complete eradication 1
Women with documented GBS bacteriuria do NOT need repeat vaginal-rectal screening at 35-37 weeks—they automatically qualify for intrapartum antibiotic prophylaxis 1, 8
Treatment Escalation Scenarios
For pyelonephritis or upper tract infection, initiate IV ampicillin 50 mg/kg every 6 hours and treat for 10-14 days, with transition to oral therapy after clinical improvement 2, 1
If bacteremia is documented, ensure at least 7-10 days of effective therapy and consider extending to 14 days if there is delayed clinical response or concern for endovascular seeding 3, 4
For recurrent GBS UTI within 30 days, obtain repeat culture with susceptibilities and consider a 10-14 day course with an alternative agent if compliance with the initial regimen was adequate 1
Common Pitfalls to Avoid
Do not use nitrofurantoin for GBS UTI—while it has excellent activity against E. coli, it should not be relied upon for streptococcal species and does not achieve therapeutic blood levels for upper tract or systemic infections 1
Do not treat asymptomatic GBS bacteriuria in non-pregnant adults—treatment is only indicated for symptomatic infection or in pregnancy 2, 1
Do not automatically extend treatment beyond 7-10 days without clear indication—recent evidence shows shorter courses (7 days) are non-inferior to 14-day regimens for uncomplicated bacteremia when appropriate antibiotics are used 3, 4