Antiamoebic drugs for treating amoebic colitis

  • Protocol
  • Intervention


  • Maria Liza M Gonzales,

    Corresponding author
    1. College of Medicine-Philippine General Hospital, University of the Philippines, Department of Pediatrics, Manila, National Capital Region, Philippines
    • Maria Liza M Gonzales, Department of Pediatrics, College of Medicine-Philippine General Hospital, University of the Philippines, Taft Avenue, Manila, National Capital Region, 1000, Philippines.

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  • Leonila F Dans,

    1. Philippine General Hospital, University of the Philippines, Department of Pediatrics and Clinical Epidemiology, Manila, National Capital Region, Philippines
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  • Elizabeth G Martinez

    1. College of Medicine-Philippine General Hospital, University of the Philippines, Department of Pediatrics, Manila, National Capital Region, Philippines
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This is a protocol for a Cochrane Review (Intervention). The objectives are as follows:

To evaluate antiamoebic drugs for treating amoebic colitis.



Amoebiasis is a parasitic disease of worldwide public health importance. It is caused by Entamoeba histolytica, a protozoan parasite distributed throughout the world. About 500 million individuals worldwide have been estimated to be infected with either E. histolytica or E. dispar, a genetically distinct species that appears identical to E. histolytica under the microscope but which never causes symptoms of disease (Walsh 1986; WHO 1997). Using biochemical, immunological, and genetic techniques that are able to differentiate the two species, 40 to 50 million people infected with E. histolytica have been estimated to develop amoebic colitis or extraintestinal abscesses that result in up to 100,000 deaths per year (Walsh 1986; Li 1996; WHO 1997; Petri 2000). Amoebiasis is second only to malaria in mortality due to protozoan parasites (WHO 1997). Prevalence rates of amoebiasis are highest in developing countries. High rates of amoebic infection have been reported from Asia, particularly the Indian subcontinent and Indonesia, the sub-Saharan and tropical regions of Africa, and areas of Central and South America (Petri 1999). In these areas, seroprevalence rates ranging from 5% to 35% have been reported (Cross 1980; Hossain 1983; Jackson 1985; Salcedo 1994; Braga 1996; Haque 1999; Blessman 2002). In developed countries, infection occurs primarily among travellers to endemic regions, recent immigrants from endemic regions, homosexuals, immunosuppressed persons, and institutionalized individuals (Reed 1992; Petri 1999). Infection is commonly acquired by ingestion of food or water contaminated with cysts of E. histolytica, but transmission also occurs through oral and anal sex, and contaminated enema apparatuses (Li 1996; Stanley 2003).

Clinical manifestations

Approximately 90% of people infected with E. histolytica have no symptoms of disease and spontaneously clear their infection, while the remaining 10% develop invasive disease (Walsh 1986; Gathiram 1987; Haque 2002; Stanley 2003). The most common manifestation of disease is intestinal amoebiasis. Intestinal disease caused by E. histolytica presents as ulcers and inflammation of the colon. This results in a complete spectrum of colonic signs and symptoms ranging from diarrhoea and acute dysentery with bloody mucoid stools to fulminating or necrotizing colitis with intestinal perforation and peritonitis (Patterson 1982; Petri 1999; Ravdin 2000). Clinical symptoms of amoebic colitis include abdominal pain or tenderness, urgency to defecate, fever, weight loss, and diarrhoea or loose stools with mucus and/or blood (WHO 1997; Haque 2003). Amoebic colitis includes two clinical forms defined by the WHO Expert Committee on Amoebiasis as 'amoebic dysentery' and 'nondysenteric amoebic colitis' (WHO 1969). Amoebic dysentery is diarrhoea with visible blood and mucus in stools and the presence of E. histolytica trophozoites with ingested red blood cells (haematophagous trophozoite) in stools or tissues; sigmoidoscopic examination reveals inflamed mucosa with or without discrete ulcers. Nondysenteric amoebic colitis presents as recurrent bouts of diarrhoea with or without mucus but no visible blood and presence of E. histolytica cysts or trophozoites with no ingested red blood cells (nonhaematophagous trophozoite) in stools; results of sigmoidoscopic examination are usually normal.

The most severe complication of amoebic colitis is fulminant or necrotizing colitis. It occurs in 0.5% of cases (Petri 1999) and as many as 6% to 11% of people with symptomatic infection (Pelaez 1966; Brooks 1985). In fulminant or necrotizing colitis, there is profuse bloody diarrhoea, fever, and widespread abdominal pain, frequently progressing to severe injury of the bowel wall, intestinal haemorrhage, or perforation with peritonitis (Haque 2003; Stanley 2003). Among these people, the case-fatality rate is more than 40% (Ellyson 1986; Petri 1999; Chen 2004). Young children, malnourished individuals, pregnant women, immunocompromised individuals, and those receiving corticosteroids are at higher risk for fulminant invasive disease (Adams 1977; Ellyson 1986; Li 1996; Stanley 2003). Extraintestinal complications of amoebic infection include liver abscess, splenic abscess, brain abscess, empyema, and pericarditis (Petri 1999; Ravdin 2000). In the treatment of fulminant or necrotizing colitis and extraintestinal amoebiasis, surgery and additional antibiotics may be required aside from specific antiamoebic drugs (WHO 1985; Stanley 2003).

Method of diagnosis

In many countries where amoebiasis is endemic, diagnosis of amoebic colitis is commonly made by identifying cysts or motile trophozoites on a saline wet mount of a stool specimen. Fresh specimens are examined in a drop of normal saline and examined for motile haematophagous trophozoites of E. histolytica. Cysts only may be found in mild cases. Finding trophozoites containing ingested red blood cells in the stool is considered by many to be diagnostic for amoebic colitis (Gonzalez-Ruiz 1994; WHO 1997). The limitations of this method include its low sensitivity and specificity because it is incapable of differentiating E. histolytica from nonpathogenic species such as E. dispar or E. moshkovskii (Petri 2000; Haque 2003). The accuracy of microscopic methods is highly dependent on the competence of the diagnostic laboratory. Specific and sensitive means to detect E. histolytica in stools include stool antigen detection test specific for E. histolytica and polymerase chain reaction (PCR) techniques based on the amplification of the parasite rRNA gene (Petri 2000). Ideally, positive stool samples should be confirmed with stool antigen or PCR before treatment starts. Unfortunately, these tests are not routinely used and are not widely available for the diagnosis of amoebic colitis in many developing countries.

Since the carriage of E. histolytica is common, its presence in stool may be incidental to bloody diarrhoea caused by other pathogens such as Shigella, Salmonella, Campylobacter, and enteroinvasive and enterohaemorrhagic Escherichia coli. A thorough workup that rules out other causes of the presenting illness is essential in patients suspected to have amoebic colitis, particularly since the signs and symptoms of amoebic colitis are nonspecific (Cooperstock 1992; Petri 2000).

Public health and socioeconomic impact

In addition to being a potentially fatal disease, invasive amoebiasis has important social and economic consequences. The peak incidence of amoebic colitis is among children less than 14 years of age and a second increase is in adults more than 40 years old (Gathiram 1985; Wanke 1988). Amoebic colitis is a temporarily incapacitating disease that may require hospitalization in some individuals presenting with severe diarrhoea or dysentery. In some developing countries, such as Mexico and Venezuela, up to 15% of all cases of acute diarrhoea and dysentery in children requiring hospitalization were found to be associated with E. histolytica (WHO 1987). Those with severe malnutrition are at greatest risk of a fatal outcome. Persistent infection can also impair physical and mental growth, and affect the nutrition and general development of children. Amoebic colitis affects adults in the wage-earning group and those with severe disease may require several weeks of hospitalization and up to two to three months for full recovery (WHO 1985).

Antiamoebic drugs for treatment

The goals of treatment for invasive amoebiasis, including amoebic colitis, are two-fold. The first is to treat the invasive disease, and the second is to eradicate intestinal carriage of the organism (Li 1996). E. histolytica may be found in the bowel lumen, in the bowel wall, and in tissues, including the liver (WHO 1969). Antiamoebic drugs vary in efficacy at the three sites where the parasites commonly exist and are generally divided into two classes based on their main site of activity. The luminal amoebicides act principally in the bowel lumen and the tissue amoebicides act principally in the bowel wall and the liver; see Appendix 1 for examples.

Metronidazole is the recommended drug for treating invasive amoebiasis, such as those with amoebic dysentery (WHO 1985; WHO 1994; WHO 2005). Other nitroimidazole drugs with longer half lives, such as tinidazole, ornidazole, and secnidazole, allow shorter periods of treatment and appear to be better tolerated compared with metronidazole, but they are not available in many countries (AAP 2003; Haque 2003; Stanley 2003; Medical Letter 2004). Emetine and its synthetic derivative dehydroemetine were widely used to treat those with severe amoebic dysentery and extraintestinal amoebiasis (WHO 1985; WHO 1995). However, because of toxicity, these drugs have largely been replaced by metronidazole and recent recommendations do not advise the use of emetine or dehydroemetine unless metronidazole is ineffective or contraindicated (Tracy 2001; Medical Letter 2004). Luminal agents are generally recommended for the treatment of asymptomatic intestinal colonization with E. histolytica or after giving a tissue amoebicide to eradicate the infection. All patients with invasive amoebiasis require treatment with a tissue amoebicide followed by a luminal amoebicide in order to eliminate any surviving organisms in the colon and to prevent relapse (WHO 1995; WHO 1997; AAP 2003; Medical Letter 2004). Relapse is defined as reappearance of cysts or trophozoites of E. histolytica, after the initial disappearance, with or without recurrence of clinical signs or symptoms of amoebic colitis after completion of therapy. In non-endemic areas where the possibility of reinfection is low, relapse in asymptomatic and chronic intestinal amoebiasis frequently occurs within one month of completion of treatment (Woodruff 1967). In endemic areas, the distinction between reinfection may be impossible, but recurrence during the follow-up period between four and six weeks after completing treatment is more likely due to relapse than to reinfection (Powell 1969).

A recent systematic review summarized the effects of different drug treatments for amoebic dysentery in endemic areas (Dans 2004). The review of randomized controlled trials reported that the nitroimidazole drugs (metronidazole, ornidazole, secnidazole, and tinidazole) were likely to be beneficial in the treatment of amoebic dysentery, while emetine and paromomycin remained of unknown effectiveness. The review did not include the other antiamoebic drugs, such as diiodohydroxyquin, diloxanide furoate, dichloroacetanilide, and etofamide, or the newer drugs quinfamide and nitazoxanide. The results of the trials were not combined, and no formal statistical methods were performed to determine summary measures of the effectiveness of the drugs.

Adequate therapy for amoebic colitis is necessary to reduce severity of illness, prevent the development of complicated disease and extraintestinal spread, and decrease infectiousness and transmission to others. In developing countries, where amoebiasis is common and most of the patients are treated in private practice or as hospital outpatients, the aim of treatment should be towards an effective, safe, and simple regimen that can be given on an outpatient basis. A reliable summary of the evidence is needed to determine the best treatment regimen for amoebic colitis. Furthermore, the benefits of using multiple antiamoebic drugs or combining drugs to treat amoebic colitis need to be ascertained.


To evaluate antiamoebic drugs for treating amoebic colitis.


Criteria for considering studies for this review

Types of studies

Randomized controlled trials.

Types of participants

Adults and children with clinical symptoms of amoebic colitis (as outlined in Haque 2003 and WHO 1997) and the demonstration of E. histolytica cysts or trophozoites in a stool sample or E. histolytica trophozoites in a tissue biopsy or ulcer scraping by histopathology.

We will exclude trials that include only individuals with asymptomatic infection and those requiring surgery or additional antibiotic therapy, such as fulminant or necrotizing colitis; peritonitis, intestinal perforation, or haemorrhage; or evidence of extraintestinal amoebiasis including hepatic amoebiasis.

Types of interventions


Antiamoebic drugs, administered alone or in combination.


Placebo or another antiamoebic drug.

Types of outcome measures

  • Clinical failures, defined as the absence of E. histolytica in stools or scrapings but little or no relief of signs or symptoms or with persistent rectal ulcerations on sigmoidoscopy (WHO 1969).

  • Parasitological failures, defined as the persistence of E. histolytica cysts or trophozoites in stools or colonic ulcer scrapings with or without presence of symptoms or rectal ulcers (WHO 1969).

  • Relapse, defined as reappearance of cysts or trophozoites of E. histolytica after the initial disappearance, with or without recurrence of clinical signs or symptoms of amoebic colitis after completion of treatment (Woodruff 1967).

Adverse events
  • Serious adverse events (death, life-threatening event, requires hospitalization or duration of hospitalization prolonged, develops a persistent or significant disability or incapacity, has offspring with a congenital anomaly or birth defect, or develops cancer (Hutchinson 1997)).

  • Adverse events resulting in discontinuation of the treatment.

  • Other adverse events, including gastrointestinal adverse events, systemic symptoms such weakness or fatigue, central nervous system effects such as headache or dizziness, and dermatologic effects such as skin rashes.

Search methods for identification of studies

We will attempt to identify all relevant trials regardless of language or publication status (published, unpublished, in press, and in progress).


We will search the following databases using the search terms and strategy described in Appendix 2: Cochrane Infectious Disease Group Specialized Register; Cochrane Central Register of Controlled Trials (CENTRAL), published in The Cochrane Library; MEDLINE; EMBASE; and LILACS. We will also search the metaRegister of Controlled Trials (mRCT) using 'amoebic' and 'amoeba' as search terms.

Conference proceedings

We will search the following conference proceedings for relevant abstracts: 24th International Congress of Chemotherapy, Manila, Philippines, 4 to 6 June 2005; 44th Interscience Conference on Antimicrobial Agents and Chemotherapy, Washington DC, USA, 2 October to 2 November 2004; 45th Interscience Conference on Antimicrobial Agents and Chemotherapy, Washington DC, USA, 16 to 19 December 2005; 52nd Annual Meeting of the American Society of Tropical Medicine and Hygiene, Philadelphia, Pennsylvania, USA, 3 to 7 December 2003; 53rd Annual Meeting of the American Society of Tropical Medicine and Hygiene, Florida, USA, 7 to 11 November 2004; 11th International Congress on Infectious Diseases, Cancun, Mexico, 4 to 7 March 2004; and the 5th European Congress of Clinical Microbiology and Infectious Diseases, Copenhagen, Denmark, 2 to 5 April 2005.

Researchers, organizations, and pharmaceutical companies

To help identify unpublished and ongoing trials, we will contact individual researchers working in the field and the following organizations: World Health Organization; American Society of Tropical Medicine and Hygiene; International Society of Tropical Pediatrics; the International Center for Diarrheal Disease Research in Bangladesh; and the South East Asian Ministers Education Organization (SEAMEO) TROPMED Network. We will also contact pharmaceutical companies including Searle (metronidazole, Flagyl), Pfizer (metronidazole, Anerobia; etofamide, Kitnos), Sandoz (metronidazole, Servizol), Presutti (tinidazole, Tindamax), Roche (ornidazole, Tiberal), Aventis (secnidazole, Flagentyl), Boots (diloxanide furoate, Furamide), Monarch (paromomycin, Humatin), Glenwood (iodoquinol, Yodoxin), Romark (nitazoxanide, AliniaTM), Roberts (furazolidone, Furozone), Sanofi (chloroquine, Aralen), CIBA Ltd (niridazole, Ambilhar), Hoffmann-la Roche & Co. Ltd (oral and injectable dehydroemetine), and Sterling Winthrop (quinfamide).

Reference lists

We will also check the reference lists of all studies identified by the above methods.

Data collection and analysis

Selection of studies

The first two authors will independently assess the results of the literature search to determine whether the title or abstract of each trial cited randomized controlled trials. We will retrieve the full reports of all trials considered by one or both authors to be potentially relevant as well as those that are unclear. We will use a standard eligibility form based on the inclusion criteria to independently assess the trials. We will resolve disagreements through discussion, or if this fails, by consulting the third author. If eligibility is unclear due to unclear or inadequate information, we will attempt to contact the trial authors for clarification. The reason for excluding studies will be noted.

Data extraction and management

The first two authors will independently extract data from the trials using pre-tested data extraction forms. We will extract the inclusion and exclusion criteria for the participants, treatment intervention given, total number randomized, number of participants in each group for all outcomes, dropouts and withdrawals, and numbers experiencing each outcome. Any disagreements about data extracted will be resolved by referring to the trial report and by discussion, or if this fails, by consultation with the third author. Where data are insufficient or missing, attempts will be made to contact the trial authors. The first two authors will enter data into Review Manager 5 using double data entry.

Assessment of risk of bias in included studies

The first two authors will independently assess the risk of bias (methodological quality) of each trial using a prepared methodological quality form. We will assess the generation of allocation sequence and allocation concealment as adequate, inadequate, or unclear according to Jüni 2001. We will note who was blinded, such as the trial participants, care providers, or outcome assessors, and assess the inclusion of randomized participants in the analysis as adequate if 90% or greater and inadequate if not. We will present the results of the assessment in tables, and use the assessment to perform a sensitivity analysis to examine the effect of trials with higher methodological quality, should there be sufficient trials.

Assessment of reporting biases

We will look for asymmetry in a funnel plot of the standard error plotted against the risk ratio measured on a logarithmic scale as an indication of publication bias. Asymmetry in the funnel plot, however, may not only indicate publication bias but also may indicate heterogeneity and poor methodological quality of smaller studies.

Data synthesis

We will analyse the data using Review Manager 4.2. We will calculate and express the clinical and parasitological failure rates and the adverse events rates as risk ratios with 95% confidence intervals.

Stratification of results

The main comparisons will be between any antiamoebic drug and placebo, any antiamoebic drug and metronidazole (current standard therapy), and any antiamoebic drug and another antiamoebic drug. Due to the variety of combinations of different treatments and different comparators, it may not be possible to combine all included trials in a single meta-analysis. When there is more than one trial comparing similar interventions and comparison groups, we will prepare separate meta-analyses for each combination: (1) an antiamoebic drug versus another antiamoebic drug belonging to the same or different drug class; (2) antiamoebic drugs grouped by drug class versus other antiamoebic drugs belonging to a different drug class; and (3) monotherapy with any antiamoebic drug versus combination drug therapy with two or more different drugs given together or sequentially.

Since trials may report results at multiple or varying time points, separate analyses will be performed for clinical and parasitological outcomes reported at the end of treatment until seven days after treatment and for outcomes reported eight to 21 days after treatment. Relapse will be measured on the third to sixth week after treatment. Relapse is defined as reappearance of cysts or trophozoites of E. histolytica after their initial disappearance with or without the recurrence of clinical signs or symptoms of amoebic colitis during follow up.

Subgroup analysis and investigation of heterogeneity

We will calculate risk ratios for individual trial outcomes and a summary risk ratio for trials in the different subgroups. When there is no statistical heterogeneity, we will use the fixed-effect model (Mantel-Haenszel method). When there is statistical heterogeneity, we will use the random-effects model (DerSimonian and Laird method) and explore the possible sources of heterogeneity. Since the ability of the diagnostic tests used to differentiate E. histolytica from E. dispar and to exclude other enteric pathogens as the cause for the intestinal symptoms may influence the rate of treatment failure and relapse, the use of different diagnostic methods as a possible source of heterogeneity will be ascertained. The presence of statistical heterogeneity among the same interventions will be determined by looking at the forest plot and by performing chi-squared test for heterogeneity using a P value of 0.10 to determine statistical significance. The I 2 test will also be used to quantify inconsistency across trials and a value greater than 50% will be considered as substantial heterogeneity.

We will perform sensitivity analyses to assess the robustness of the meta-analysis among the same interventions by calculating the results using all trials and then excluding trials of a lower methodological quality (ie trials with inadequate generation of allocation sequence and allocation concealment, trials that were not double blind, and trials where less than 90% of randomized participants were analysed).


None stated.


Appendix 1. Amoebicide classes and examples

LuminalArsenical compoundsCarbarsone, acetarsone or acetarsol, treparsol, diphetarsone, glycobiarsol or bismuth glycoarsanilate, stovarsol, and thioarsenite (thiocarbarsone, arsthinol)
Hydroxyquinoline derivativesChiniofon or quinoxyl, clioquinol or iodochlorhydroxyquin, and iodoquinol or diiodohydroxyquin
Dichloroacetamide derivativesDiloxanide furoate or entamide furoate, clefamide or eticlordifene, quinfamide, and etofamide or etophamide
Benzylamine derivativesTeclozan, chlorbetamide or mantomide, and chlorphenoxamide or mebinol
Antibiotic amoebicidesTetracycline, oxytetracycline, chlortetracycline, erythromycin, paromomycin, and fumagillin
Nithrothiazole salicylamideNitaxozanide
TissueEmetine and its derivativesEmetine hydrochloride, emetine bismuth iodide, dehydroemetine dihydochloride, and dehydroemetine resinate
Thiazole derivativeNiridazole
NitroimidazolesMetronidazole, tinidazole, ornidazole, secnidazole, and nimorazole

Appendix 2. Search methods: detailed search strategies

31 or 21 or 21 OR 2EMETINE1 or 2
4nitroimidazolesamoebicidesAMEBICIDES/THERAPEUTIC USEDILOXANIDE FUROATEnitroimidazoles
6diloxanide furoateemetineEMETINEacetarsonediloxanide furoate
7quinfamidediloxanide furoatecarbarsoneacetarsolquinfamide
12tetracyclineARSENICALSstovarsoldiloxanide furoatetetracycline
14niridazoletetracyclinediloxanide furoateetofamideniridazole
173 AND 16erythromycinetophamideclioquinol3 AND 16
213 AND 20dichloroacetamidechloroquine
31nimorazole1 AND 30
32nitrimidazineLimit 31 to human
343 AND 33
35Limit 34 to human

aCochrane Infectious Diseases Group Specialized Register.
bSearch terms used in combination with the search strategy for retrieving trials developed by The Cochrane Collaboration (Higgins 2005); upper case: MeSH or EMTREE heading; lower case: free text term.

What's new

11 November 2008AmendedConverted to new review format with minor editing.

Contributions of authors

Dr MLM Gonzales is primarily responsible for conceiving and designing the review, and co-ordinating its development. Dr LF Dans has advised the first author about the design and co-ordination of the review. Dr EG Martinez will act as the third author in the resolution of any differences in assessment of papers between the other two authors. Dr EG Martinez and Dr L Dans conducted the systematic review on drug therapy for amoebic dysentery (Dans 2004) that set the groundwork for this Cochrane Review.

Declarations of interest

None known.

Sources of support

Internal sources

  • No sources of support supplied

External sources

  • Department for International Development (DFID), UK.