Antiamoebic drugs for treating amoebic colitis

Amoebic colitis is caused by the parasite Entamoeba histolytica. This protozoan is distributed throughout the world and is commonly acquired by ingestion of contaminated food or water. It is estimated that about 40 to 50 million people infected with E. histolytica develop amoebic colitis or extraintestinal abscesses, which result in up to 100,000 deaths per year.

Metronidazole is currently the drug of choice for treating invasive amoebiasis in adults and children, but it may not be sufficient to eliminate parasite cysts in the intestine. Combinations with other drugs are therefore also used. However, the evidence to support combination therapy has not been reviewed. Also, some unpleasant adverse effects associated with metronidazole in some patients, and the possibility of parasite resistance to metronidazole has to be considered.

This review compares different drugs used against amoebic colitis, alone or in combination, and also assesses single-dose regimens versus longer regimens.

Thirty-seven trials with 4487 participants were included, and only one was of high methodological quality. Tinidazole reduced clinical failure compared with metronidazole and was associated with fewer adverse events. Combination therapy resulted in fewer parasitological failures than metronidazole alone.

The authors conclude that tinidazole appears more effective at reducing clinical failures than metronidazole, and has fewer associated adverse events. There is insufficient evidence to draw conclusions regarding the efficacy of the other antiamoebic drugs. However, the trials' methodological quality was generally inadequate. Also, the choice of antiamoebic drugs would depend largely on the availability and accessibility of drugs.

Better quality randomized trials with standardized outcomes are needed to evaluate the efficacy of drugs for treating amoebic colitis. There is also a need for improved, reliable diagnostic tests that can be used in developing countries.

Authors' conclusions: 

Tinidazole is more effective in reducing clinical failure compared with metronidazole and has fewer associated adverse events. Combination drug therapy is more effective in reducing parasitological failure compared with metronidazole alone. However, these results are based on trials with poor methodological quality so there is uncertainty in these conclusions. Further trials of the efficacy of antiamoebic drugs, with better methodological quality, are recommended. More accurate tests to detect E. histolytica are needed, particularly in countries where concomitant infection with other bacteria and parasites is common.

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Background: 

Entamoeba histolytica infection is common in developing countries, and up to 100,000 individuals with severe disease die every year. Adequate therapy for amoebic colitis is necessary to reduce the severity of illness, prevent development of complicated disease and extraintestinal spread, and decrease transmission.

Objectives: 

To evaluate antiamoebic drugs for treating amoebic colitis.

Search strategy: 

In September 2008, we searched the Cochrane Infectious Diseases Group Specialized Register, CENTRAL (2008, Issue 3), MEDLINE, EMBASE, LILACS, mRCT, and conference proceedings. We contacted individual researchers, organizations, and pharmaceutical companies, and checked reference lists.

Selection criteria: 

Randomized controlled trials of antiamoebic drugs given alone or in combination, compared with placebo or another antiamoebic drug for treating adults and children diagnosed with amoebic colitis.

Data collection and analysis: 

Two authors independently assessed the eligibility and methodological quality of trials, and extracted and analysed the data. We calculated clinical and parasitological failure rates, relapse, and adverse events as risk ratios (RR) with 95% confidence intervals (CIs), using a random-effects model. We determined statistical heterogeneity and explored possible sources of heterogeneity using subgroup analyses. We carried out sensitivity analysis using trial quality to assess the robustness of the results.

Main results: 

Thirty-seven trials, enrolling 4487 participants, met the inclusion criteria. Only one trial used adequate methods for randomization and allocation concealment, was blinded, and analysed all randomized participants. Only one trial used a E. histolytica stool antigen test. Tinidazole reduced clinical failure compared with metronidazole (RR 0.28, 95% CI 0.15 to 0.51; 477 participants, eight trials) and was associated with fewer adverse events. Compared with metronidazole, combination therapy resulted in fewer parasitological failures (RR 0.36, 95% CI 0.15 to 0.86; 720 participants, 3 trials).

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