A 62-year-old woman with obstructive jaundice due to a common bile duct stone is found to have acute cholangitis (fever 39.2°C, RUQ tenderness, elevated WBC and bilirubin). Blood cultures are pending. She is haemodynamically stable. Which antibiotic regimen is the drug of choice for initial empiric coverage in acute cholangitis?

## Empiric Antibiotic Therapy in Acute Cholangitis **Key Point:** Ceftriaxone (or cefotaxime) + metronidazole is the gold-standard empiric regimen for acute cholangitis, providing broad coverage of gram-negative aerobes (E. coli, Klebsiella), gram-positive cocci, and anaerobes (Bacteroides, Clostridium) commonly isolated from infected bile. ### Microbiology of Infected Bile | Organism Class | Examples | Frequency | | --- | --- | --- | | **Gram-negative aerobes** | E. coli, Klebsiella, Enterobacter | 60–70% | | **Gram-positive cocci** | Enterococcus, Streptococcus | 20–30% | | **Anaerobes** | Bacteroides, Clostridium | 10–20% | | **Polymicrobial** | 2–3 organisms common | 40–50% | **High-Yield:** Enterococcus is increasingly common in elderly patients and those with prior biliary instrumentation; ceftriaxone + metronidazole does NOT reliably cover enterococcus, so ampicillin or piperacillin-tazobactam may be preferred in high-risk subgroups. ### Rationale for Ceftriaxone + Metronidazole 1. **Ceftriaxone (3rd-generation cephalosporin):** - Excellent bile penetration (60–80% of serum levels) - Covers gram-negative aerobes and gram-positive cocci - Beta-lactamase stable; active against most E. coli and Klebsiella - Dosing: 1–2 g IV q12h 2. **Metronidazole:** - Covers anaerobes (Bacteroides, Clostridium) - Good bile and tissue penetration - Dosing: 400–500 mg IV q6–8h ### Alternative Regimens by Risk Profile | Clinical Scenario | Preferred Regimen | Rationale | | --- | --- | --- | | **Mild–moderate, community-acquired** | Ceftriaxone + metronidazole | Standard empiric choice | | **Severe sepsis or high-risk (age >70, immunocompromised, prior instrumentation)** | Piperacillin-tazobactam ± gentamicin | Covers enterococcus, broader gram-negative spectrum | | **Penicillin allergy** | Fluoroquinolone (ciprofloxacin) + metronidazole | Ciprofloxacin achieves good bile levels | | **Severe renal impairment** | Adjust cephalosporin dosing; consider fluoroquinolone | Avoid aminoglycosides | **Clinical Pearl:** Start antibiotics immediately upon clinical suspicion of cholangitis (before blood cultures return); do not wait for culture results. Definitive treatment (ERCP ± sphincterotomy or percutaneous drainage) should follow within 24–48 hours. **Mnemonic:** **CEFTAZ** — **C**eftriaxone (or cefotaxime) + **E**xtra coverage (metronidazole for anaerobes) = **T**he **A**pproach for **Z**ooning in on cholangitis.