Keflex (Cephalexin) Dosing for Group B Streptococcus UTI in First Trimester Pregnancy
For pregnant women with Group B Streptococcus (GBS) urinary tract infection in the first trimester, the recommended dosage of Keflex (cephalexin) is 500 mg orally every 6 hours for 7-10 days. 1
Rationale for Treatment
GBS in urine during pregnancy requires immediate attention because:
- Any amount of GBS in urine during pregnancy indicates heavy colonization
- Treatment is necessary both for the current infection and to prevent complications
- Untreated GBS UTI increases risks of premature rupture of membranes and preterm labor
Antibiotic Selection
Cephalexin (Keflex) is an appropriate first-line choice for GBS UTI in pregnancy for several reasons:
- First-generation cephalosporins are effective against GBS
- Cephalexin reaches high bactericidal concentrations in the urinary tract 2
- It has an established safety profile in pregnancy
- It demonstrates minimal induction of resistance in the vaginal flora 3
Treatment Duration
- For uncomplicated GBS UTI: 7-10 days of treatment 1
- For complicated UTI or pyelonephritis: 10-14 days of treatment 1
- Treatment should continue for at least 48-72 hours after symptom resolution 1
Alternative Options
If penicillin allergy is present (without anaphylaxis risk):
- Cefazolin: 2 g IV initial dose, then 1 g IV every 8 hours 1
If high risk of anaphylaxis:
- Clindamycin: 900 mg IV every 8 hours (only if susceptibility testing confirms sensitivity) 1
- Vancomycin: 1 g IV every 12 hours (for clindamycin-resistant strains) 1
Follow-up Recommendations
- Obtain a urine culture after completing treatment to confirm eradication 1
- Intrapartum prophylaxis will still be required during labor regardless of successful treatment earlier in pregnancy 1
- No need to re-screen with vaginal-rectal cultures at 35-37 weeks for women with GBS bacteriuria during pregnancy 1
Important Clinical Considerations
- GBS in urine during pregnancy is significant at any colony count and always requires treatment 1
- Nitrofurantoin may be effective for uncomplicated lower UTIs but is not preferred for GBS 1
- Fluoroquinolones should be avoided during pregnancy due to potential adverse effects 1
- Tetracyclines are contraindicated in pregnancy 1
Pitfalls to Avoid
- Failing to treat GBS bacteriuria during pregnancy, even if asymptomatic
- Using inadequate treatment duration (less than 7 days)
- Not obtaining follow-up urine culture to confirm eradication
- Forgetting that intrapartum prophylaxis is still required during labor despite previous treatment
- Using antibiotics with poor urinary concentration or inadequate GBS coverage
By following these guidelines, clinicians can effectively manage GBS UTI in first trimester pregnancy while minimizing risks to both mother and fetus.