Medical Care
Most uncomplicated amebic liver abscesses can be treated successfully with conservative management, [30] such as with amebicidal drug therapy alone. Use tissue amebicides to eradicate the invasive trophozoite forms in the liver. After completion of treatment with tissue amebicides, administer luminal amebicides for eradication of the asymptomatic colonization state. Failure to use luminal agents can lead to relapse of infection in approximately 10% of patients.
In general, metronidazole, tinidazole, emetine, and dehydroemetine are active in invaded tissues; chloroquine is active only in the liver; tetracycline acts on the bowel wall; and diloxanide furoate, paromomycin, and iodoquinol are luminal agents only. The details on tissue and luminal amebicidal agents are discussed in Medication.
Metronidazole
Metronidazole remains the drug of choice for amebic liver abscess. Metronidazole enters the protozoa by passive diffusion and is converted to reactive cytotoxic nitroradicals by reduced ferredoxin or flavodoxin. Tinidazole, another nitroimidazole closely related to metronidazole, was approved for the treatment of amebic liver abscess and invasive amebiasis. Tinidazole is well tolerated by patients. Tinidazole may be administered once daily and appears to be at least as effective as metronidazole, with a clinical cure rate of more than 90%.
Metronidazole, 750 mg 3 times a day orally for 10 days, was reported to be curative in 90% of patients with amebic liver abscess. The drug also is available for intravenous administration for those patients who are unable to take the medication by the oral route.
Resolution of symptoms is fairly rapid and is observed within 3 days in most patients in the United States. In endemic areas outside the United States, it takes relatively longer to resolve the symptoms because the abscesses are quite large or multiple by the time patients seek medical attention.
In vivo E histolytica resistance to metronidazole has not been reported. Nevertheless, in vitro studies have shown an association between metronidazole resistance and decreased expression of ferredoxin 1 and flavodoxin and increased expression of iron-containing superoxide dismutase and peroxiredoxin in E histolytica.
Usual adverse effects of metronidazole include nausea, headache, and metallic taste. Abdominal cramps, vomiting, diarrhea, and dizziness also may occur. Dark urine caused by a metabolite of the drug may be observed.
Other items to consider
Other considerations include the following:
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No randomized controlled trials exist that demonstrate the benefits of combination therapy over monotherapy.
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Outside the United States, other closely related amebicidal agents, such as secnidazole or ornidazole, can be substituted in appropriate dosages. These drugs are not available in the United States.
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Chloroquine phosphate may be substituted or added in the event of failure of resolution of clinical symptoms with metronidazole or another nitroimidazole within 5 days, or intolerance to metronidazole or a nitroimidazole. Chloroquine has the disadvantage of being associated with higher relapse rates than nitroimidazoles. Adverse effects include gastrointestinal upset, headache, dizziness, and blurred vision. Retinopathy does not occur at the dose used for amebic liver abscess.
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Emetine or dehydroemetine has a direct lethal action on the trophozoites of E histolytica. These agents are very toxic and, therefore, should be used only as a second-line therapy. Their toxicity includes cardiac arrhythmias, precordial pain, muscle weakness, vomiting, and diarrhea. Dehydroemetine is less toxic than emetine.
Administer a luminal amebicidal agent to eradicate the intestinal carriage after the amebic liver abscess has been treated with one of the tissue amebicides noted below. Failure to use luminal agents can lead to relapse of infection in approximately 10% of patients. Luminal agents with proven efficacy include diloxanide furoate, iodoquinol, and paromomycin. Note the following:
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Diloxanide furoate is free of major adverse effects. The most common adverse effect is flatulence and occasional gastrointestinal upset.
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Iodoquinol (diiodohydroxyquin) rarely causes abdominal pain, diarrhea, or rash. A structurally related diiodohydroxyquin caused subacute myelopticoneuropathy and is obsolete now.
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Although paromomycin may occasionally cause nausea, abdominal cramps, or diarrhea, it is the preferred luminal amebicidal.
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The details on the luminal amebicides are discussed in Medication.
Consultations
Consult with an interventional radiologist for imaging-guided aspiration of the abscess.
Consult with a general surgeon for open surgical drainage of the abscess under rare circumstances (see Surgical Care).
Diet and activity
No specific diet change or modification is required. However, discuss food hygiene with patients because amebiasis is associated with suboptimal personal or food hygiene (see Patient Education).
No restriction of activity is needed, except during the first few days of acute illness with pain.
If emetine or dehydroemetine is used, the patient should remain sedentary for approximately 4 weeks after completing therapy because of their toxicity.
Surgical Care
Consider therapeutic aspiration of amebic liver abscess in the following situations: (1) high risk of abscess rupture, as defined by cavity size greater than 5 cm; (2) left lobe liver abscess, which is associated with higher mortality and frequency of peritoneal leak or rupture into the pericardium; (3) failure to observe a clinical medical response to therapy within 5-7 days; and (4) cannot differentiate from a pyogenic liver abscess.
The following are predictive of the need for aspiration: (1) age older than 55 years, (2) abscess greater than 5 cm in diameter, [31] and (3) failure of medical therapy after 7 days. [32] In endemic areas, because of the late presentation and the existence of multiple abscesses, as many as 50% of patients may require aspiration. [33] However, routine needle aspiration offers only minimal benefit over medical care alone for uncomplicated amebic liver abscess and, unless one of the above indications exists, should be avoided. [34] Prompt medical care decreases the need for aspiration. [35]
Imaging-guided needle aspiration and catheter drainage are the procedures of choice. Generally, surgical drainage is not necessary and should be avoided; however, consider open surgical drainage when the abscess is inaccessible to needle drainage or a response to therapy has not occurred in 5-7 days.
Simple needle aspiration is less invasive, is less expensive, and has the advantage of being able to drain multiple abscesses in the same session. Simple needle aspiration avoids problems related to catheter care (see Procedures).
Although catheter drainage may be more effective than needle aspiration, in a study by Rajak et al, [36] the average time for clinical improvement, mean hospital stay, and time to resolution were similar among the patients who were successfully treated in the two treatment groups.
Long-Term Monitoring
Follow-up ultrasonography or computed tomography scanning is unnecessary after resolution of symptoms and signs because the radiological resolution may take several months to years. See Prognosis.
Luminal amebicides fail to eradicate the luminal forms of E histolytica in approximately 10-15% of patients treated with these agents; therefore, a follow-up stool examination is recommended after completion of therapy. A second course of a luminal amebicide is required in a few weeks if the first course fails to eradicate the intestinal carriage.
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CT scan of the abdomen with IV and oral contrast is shown. Note the thick-walled cavity with low attenuation center and contrast-enhanced periphery.
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CT scan of the abdomen with contrast showing a large amebic abscess with multiloculated appearance and atypical left liver lobe location. CT scan cannot differentiate amebic liver abscess from pyogenic liver abscess.
