## Antibiotic Prophylaxis in β-Lactam–Allergic Appendicitis **Key Point:** In patients with true β-lactam allergy (anaphylaxis), clindamycin + gentamicin is the preferred alternative for preoperative prophylaxis in acute appendicitis. ### Why Clindamycin + Gentamicin? 1. **Clindamycin**: Excellent anaerobic coverage (Bacteroides, Peptostreptococcus, Clostridium); also covers gram-positive cocci. 2. **Gentamicin**: Provides gram-negative aerobic coverage (E. coli, Klebsiella, Enterobacter). 3. **No cross-reactivity**: Both agents are non-β-lactam, safe in true penicillin/cephalosporin allergy. 4. **Established use**: Standard alternative regimen in surgical prophylaxis guidelines for β-lactam–allergic patients. ### Dosing for Prophylaxis | Drug | Dose | Timing | |------|------|--------| | **Clindamycin** | 600 mg IV | Within 60 min of incision | | **Gentamicin** | 5 mg/kg IV | Within 60 min of incision | | **Redosing** | If surgery > 2 half-lives | — | **High-Yield:** Gentamicin dosing in prophylaxis is weight-based (5 mg/kg); monitor renal function. In patients with renal impairment, dosing intervals must be adjusted. **Clinical Pearl:** Cross-reactivity between penicillins and cephalosporins is ~1–3% in non-anaphylactic allergy; however, in true anaphylaxis, avoid all β-lactams. Carbapenems (e.g., meropenem) have ~1% cross-reactivity with penicillins and may be considered if allergy is mild, but clindamycin + gentamicin is safer and preferred. ### Why Not the Other Options? **Vancomycin + metronidazole**: Vancomycin is reserved for serious infections (e.g., MRSA) and is not first-line prophylaxis. It increases cost and risk of nephrotoxicity without added benefit in uncomplicated appendicitis. **Fluoroquinolone monotherapy**: Inadequate anaerobic coverage; not suitable as sole agent for appendicitis prophylaxis. **Aztreonam + metronidazole**: Aztreonam is a monobactam with minimal cross-reactivity to β-lactams, but it is not standard first-line and is more expensive than clindamycin + gentamicin. [cite:Sabiston Textbook of Surgery Ch 51; Harrison 21e Ch 297]
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