A 28-year-old woman presents with a 3-week history of fever, right upper quadrant pain, and hepatomegaly. Ultrasound shows a 6 cm hypoechoic lesion in the right lobe of the liver with a positive halo sign. Serology is positive for anti-E. histolytica IgG antibodies. What is the drug of choice for amebic liver abscess?

Explanation

## Treatment of Amebic Liver Abscess ### Pathophysiology & Clinical Context Amebic liver abscess (ALA) is an extraintestinal manifestation of invasive amebiasis caused by *Entamoeba histolytica* trophozoites that invade the intestinal mucosa, enter the portal circulation, and lodge in hepatic tissue. The abscess contains sterile pus (trophozoites are at the periphery) and can rupture into the peritoneal cavity or pleural space if untreated. **Key Point:** Amebic liver abscess requires a two-stage treatment approach: first, a tissue-penetrating agent (metronidazole) to kill trophozoites in the abscess and liver parenchyma; second, a luminal agent (paromomycin or iodoquinol) to eliminate any remaining intestinal cysts and prevent relapse. ### Standard Regimen for Amebic Liver Abscess | Drug | Dose | Duration | Rationale | |------|------|----------|----------| | **Metronidazole** | 750 mg TDS (or 400 mg QID) | 7–10 days | Excellent tissue penetration; kills trophozoites in abscess wall | | **Paromomycin** | 25–35 mg/kg/day in 3 doses | 7 days | Luminal agent; eliminates cysts from bowel lumen | **High-Yield:** Metronidazole achieves high concentrations in liver tissue and abscess fluid (20–50 times serum level). It resolves fever and systemic symptoms within 72 hours in most cases. ### Why This Two-Stage Approach? 1. **Metronidazole** — kills trophozoites in tissue (abscess, liver parenchyma, portal blood) 2. **Paromomycin** — eliminates cysts in the intestinal lumen (prevents relapse and transmission) Omitting the luminal stage results in 5–10% relapse rates; the combination reduces relapse to <1%. ### Adjunctive Measures - **Aspiration:** Reserved for abscesses >5 cm, imminent rupture, or failure to improve after 72 hours of therapy - **Imaging:** Ultrasound or CT to monitor abscess size (may persist for weeks despite clinical improvement) - **Stool examination:** Perform after treatment to confirm cyst clearance **Clinical Pearl:** Do NOT use chloroquine as monotherapy for ALA — it accumulates in liver but is less effective than metronidazole and is now considered second-line or obsolete in most guidelines. [cite:Harrison 21e Ch 229; KD Tripathi 8e Ch 51]