Can doxycycline (tetracycline antibiotic) be used to treat Group B strep (Streptococcus agalactiae) urinary tract infection (UTI)?

Treatment of Group B Streptococcal UTI

Doxycycline should not be used to treat Group B Streptococcal (GBS) urinary tract infections due to high resistance rates and availability of more effective alternatives. 1, 2, 3

First-Line Treatment Options for GBS UTI

Penicillins remain the treatment of choice for GBS UTIs due to their proven effectiveness and narrow spectrum of activity:

• First choice: Penicillin G (5 million units IV initial dose, then 2.5-3.0 million units IV every 4 hours) 1
• Alternative: Ampicillin (2g IV initial dose, then 1g IV every 4 hours) 1

For less severe, uncomplicated outpatient cases:

• Oral amoxicillin or penicillin V can be used 1

Treatment for Penicillin-Allergic Patients

For patients with penicillin allergy:

• Non-severe allergy: Cefazolin (2g IV initial dose, then 1g IV every 8 hours) 1
• Severe allergy (history of anaphylaxis, angioedema, respiratory distress, or urticaria):
  • Clindamycin (900mg IV every 8 hours) - only if susceptibility testing confirms sensitivity 4, 1
  • Vancomycin (1g IV every 12 hours) - if susceptibility testing unavailable or resistance to clindamycin 4, 1

Why Not Doxycycline?

Doxycycline (and tetracyclines in general) should be avoided for GBS UTIs for several important reasons:

1. High resistance rates: Multiple studies show tetracycline resistance rates of 72-88% among GBS isolates 5, 2, 3
2. Historical context: Tetracycline resistance in GBS is widespread due to extensive tetracycline use since the 1940s, which led to selection of resistant clones 6
3. Genetic basis: Tetracycline resistance in GBS is often plasmid-mediated, making it highly transmissible 7

Special Considerations

Pregnant Women

• GBS bacteriuria during pregnancy requires prompt treatment as it indicates heavy colonization and increases risk of preterm delivery 1
• Tetracyclines are contraindicated in pregnancy and in children <8 years of age 4
• Follow GBS screening protocols at 35-37 weeks regardless of previous GBS UTI treatment 1

Antibiotic Stewardship

• Avoid fluoroquinolones for uncomplicated UTIs when alternatives exist, due to FDA warnings about serious side effects 4
• Nitrofurantoin may be effective for uncomplicated lower UTIs caused by GBS 4, 3

Follow-up Recommendations

• Obtain urine culture after completion of treatment to confirm eradication 1
• Do not treat asymptomatic GBS colonization outside of pregnancy 1
• For recurrent UTIs, consider longer courses of appropriate antibiotics and urologic evaluation

In conclusion, while doxycycline is an effective option for many bacterial infections, it is not appropriate for GBS UTIs due to widespread resistance. Penicillins remain the cornerstone of treatment, with specific alternatives available for those with penicillin allergies.