What are the common antibiotics used in obstetrics (OB) and gynecology (Gyne)?

Common Antibiotics Used in Obstetrics and Gynecology

Cefazolin is the cornerstone antibiotic for most obstetric and gynecologic procedures, with metronidazole added when anaerobic coverage is needed. 1

Surgical Prophylaxis

Cesarean Section

• Cefazolin 2g IV is the first-line prophylactic agent, administered as a single dose 1
• Alternative: Amoxicillin-clavulanic acid for vaginal delivery 1
• For penicillin allergy: Clindamycin 900mg IV as single dose 1, 2
• Timing: 15-60 minutes before incision 3

Hysterectomy (Abdominal or Vaginal)

• Cefazolin 2g IV + Metronidazole is the recommended combination 1
• Alternative first-generation cephalosporins: Cefamandole 1.5g IV or Cefuroxime 1.5g IV 1
• For penicillin allergy: Clindamycin 900mg IV + Gentamicin 5mg/kg 1
• Single dose prophylaxis is sufficient; re-dose if procedure exceeds 4 hours 1

Gynecologic Surgery Requiring Anaerobic Coverage

• Cefazolin + Metronidazole for procedures involving vaginal or bowel flora 1
• Metronidazole 500mg IV provides essential anaerobic coverage for Bacteroides species and Clostridium 4
• This combination is critical for endometritis, tubo-ovarian abscess, and postsurgical vaginal cuff infections 4

Treatment of Active Infections

Pelvic Inflammatory Disease (PID)

Parenteral Regimens:

• Regimen A: Cefotetan or Cefoxitin IV + Doxycycline 100mg PO/IV twice daily 1
• Regimen B: Clindamycin 900mg IV every 8 hours + Gentamicin 2mg/kg loading dose, then 1.5mg/kg every 8 hours 1
• Continue parenteral therapy for 24 hours after clinical improvement, then switch to oral doxycycline 100mg twice daily to complete 14 days 1
• For tubo-ovarian abscess: Use clindamycin for continued therapy rather than doxycycline alone for better anaerobic coverage 1

Oral Regimens:

• Ofloxacin 400mg twice daily for 14 days OR Levofloxacin 500mg once daily for 14 days, with or without Metronidazole 500mg twice daily 1
• Alternative: Ceftriaxone 250mg IM single dose + Doxycycline 100mg twice daily for 14 days ± Metronidazole 1

Chorioamnionitis and Puerperal Endometritis

• Extended-spectrum agents as single therapy: Ampicillin-sulbactam, piperacillin-tazobactam, or carbapenems provide sufficient polymicrobial coverage 5
• Combination regimens: Clindamycin or Metronidazole + Gentamicin or Aztreonam are highly effective alternatives 5, 6
• These infections are typically polymicrobial involving enterobacteria and anaerobes 6

Postoperative Surgical Site Infections

• For incisional abscess: Incision and drainage is mandatory before or concurrent with antibiotics 2
• First-line: Cefazolin 1-2g IV every 8 hours + Metronidazole 500mg IV every 6-8 hours 2
• For penicillin allergy: Clindamycin 600-900mg IV every 8 hours provides both Gram-positive and anaerobic coverage 2
• Alternative: Ampicillin-sulbactam 1.5-3g IV every 6-8 hours 2
• Continue IV antibiotics until clinical improvement, typically 5-7 days for adequately drained infections 2

Obstetric Anal Sphincter Injuries (OASIS)

• Second- or third-generation cephalosporin + Metronidazole should be administered before repair 1
• Consider adding Gentamicin for broader coverage of vaginal and bowel flora 1
• For penicillin allergy: Clindamycin is the alternative 1
• This prophylaxis significantly reduces wound complications including purulent discharge and dehiscence 1

Most Commonly Used Antibiotics in OB/GYN Practice

Based on real-world usage patterns 7:

• Metronidazole (93.33%) - Most frequently used for anaerobic coverage 7
• Ceftriaxone (68.66%) - Broad-spectrum cephalosporin, excellent for gonorrhea 7, 5, 8
• Gentamicin (60.33%) - Aminoglycoside for Gram-negative coverage 7
• Cefuroxime (48%) - Second-generation cephalosporin alternative 7
• Cefixime (27%) - Oral third-generation option 7

Common combination regimens:

• Ceftriaxone + Metronidazole + Gentamicin (37.66%) 7
• Ceftriaxone + Metronidazole (25.33%) 7
• Cefuroxime + Metronidazole + Gentamicin (16%) 7

Special Considerations

Cervicitis and Endocervical Infections

• Ceftriaxone is excellent for Neisseria gonorrhoeae 5, 8
• Azithromycin or Erythromycin for Chlamydia trachomatis 5
• Doxycycline is an alternative for chlamydial infections but avoid in pregnancy 5, 3

Procedures NOT Requiring Prophylaxis

• Diagnostic laparoscopy without bowel or vaginal entry 3
• Intrauterine device insertion 3
• Diagnostic hysteroscopy 3
• Simple breast lumpectomy 1

Obesity and Prolonged Procedures

• Adjusted doses are advised for obese patients 3
• Re-dose antibiotics if procedure duration exceeds the half-life threshold (typically >4 hours for cefazolin) 1, 3
• Re-dose for excessive blood loss (>1500mL) 3

MRSA Considerations

• Vancomycin 15-20mg/kg IV every 8-12 hours should be added if MRSA is suspected or documented 2
• Routine vancomycin prophylaxis is not recommended but may be considered for known MRSA colonization 1

Critical Pitfalls to Avoid

• Never use antibiotics alone for surgical site abscess - drainage is mandatory 2
• Do not extend prophylaxis beyond 24 hours - this becomes treatment, not prophylaxis 1
• Avoid inadequate anaerobic coverage - metronidazole or clindamycin is essential for most OB/GYN infections 1, 4
• Do not forget to obtain cultures before starting treatment for active infections 2
• Reassess if no improvement within 48-72 hours - review cultures and adjust regimen 2