Treatment of Amoebiasis (Trophozoites and Cysts)
For patients with amoebiasis presenting with both trophozoites and cysts, treat with metronidazole 750 mg orally three times daily for 5-10 days (adults) or 30 mg/kg/day divided into three doses for 5-10 days (children), followed by a mandatory luminal agent such as paromomycin 25-35 mg/kg/day divided into three doses for 7 days to eliminate intestinal cysts and prevent relapse. 1, 2, 3
Diagnostic Confirmation Before Treatment
- Do not initiate treatment unless microscopic examination of fresh feces demonstrates Entamoeba histolytica trophozoites, or two different antibiotics for shigellosis have failed after 4 days total. 4, 1, 2
- If dysentery is present but microscopy is unavailable or trophozoites are not definitively identified, treat for shigellosis first with ampicillin or TMP-SMX before considering amoebiasis. 4
- Care must be taken to distinguish large white cells (nonspecific indicator of dysentery) from actual trophozoites, as amebic dysentery tends to be misdiagnosed. 4
Two-Phase Treatment Approach
Phase 1: Tissue Amebicide (Eliminates Trophozoites)
First-line options:
- Metronidazole: 750 mg orally three times daily for 5-10 days (adults) 1, 2, 3, 5
- Metronidazole: 30 mg/kg/day divided into three doses for 5-10 days (children) 1, 2
- Alternative: Tinidazole 2 g orally once daily for 3 days (intestinal) or 5 days (liver abscess) in adults; 50 mg/kg once daily (maximum 2 g) for 3-5 days in children >3 years 2, 5
Evidence supporting tinidazole: In randomized controlled trials, tinidazole 2 g/day for 3 days achieved cure rates of 86-93% for intestinal amoebiasis 5, and was superior to metronidazole in one comparative study (92.6% vs 58.6% cure rate, p<0.01) with better tolerability. 6
Phase 2: Luminal Amebicide (Eliminates Cysts - MANDATORY)
After completing tissue amebicide therapy, ALL patients must receive a luminal agent to eradicate intestinal cysts and prevent relapse. 1, 2, 3
Luminal agent options:
- Paromomycin: 25-35 mg/kg/day orally divided into three doses for 7 days (adults and children) 2
- Alternative: Paromomycin 500 mg three times daily for 7 days (adults) 3
- Alternative: Diloxanide furoate 500 mg orally three times daily for 10 days (adults) 1, 3
Clinical Monitoring and Expected Response
- Clinical improvement should occur within 48 hours of initiating metronidazole therapy. 2, 3
- Symptoms should completely resolve within 3 months of treatment initiation. 2
- If no improvement occurs within 2 days, consider alternative diagnoses (particularly resistant shigellosis) or drug resistance. 4, 1
Special Clinical Scenarios
Amoebic Liver Abscess
- Use the same metronidazole or tinidazole regimens as for intestinal amoebiasis. 1
- Most patients respond within 72-96 hours of treatment initiation. 1
- Indirect hemagglutination testing has >90% sensitivity and should be performed in suspected cases. 1
- Surgical or percutaneous drainage is rarely required and should only be considered for diagnostic uncertainty, persistent symptoms after 4 days of treatment, or risk of imminent rupture. 1
- Still requires luminal agent follow-up to eliminate intestinal cysts. 1
Severe Ulcerative Colitis with Travel History
- For patients with acute severe ulcerative colitis who have recent travel to endemic areas, consider adding metronidazole pending stool microscopy if amoebiasis is suspected. 1
Critical Pitfalls to Avoid
Failure to provide a luminal agent after metronidazole/tinidazole therapy is the most common cause of relapse. 3 The tissue amebicide eliminates invasive trophozoites but does not eradicate intestinal cysts, which will continue to be passed and can cause reinfection or transmission. 1, 2, 3
Misdiagnosis between amebic and bacterial dysentery leads to inappropriate treatment. 4, 3 Shigellosis is more common than amoebiasis in most settings, and multiresistant Shigella strains can mimic treatment-refractory amoebiasis. 4