AMOEBICIDAL AGENTS (antiamoebic agents; amoebicides) are used to treat or prevent infections caused by amoebic microorganisms, which are small unicellular organisms that prefer damp environments.

Although now classified as part of the kingdom Protista, phylum Rhizopoda, amoebae were originally classified as Protozoa. Consequently, the term antiamoebic agent tends to be used as synonymous with ANTIPROTOZOAL AGENT, and a number of agents are effective against both.

One genus of amoebae responsible for a number of diseases are the Entamoeba, found particularly in the gastrointestinal tract of humans. E. histolytica invades and destroys the tissues of the gut wall causing amoebic dysentery and ulceration of the gut wall. Infection of the liver by this species causes amoebic hepatitis. E. gingivalis, found within the spaces between the teeth, is associated with periodontal disease and gingivitis.

In practice, treatment of amoebiasis can be divided into treatment of bowel lumen amoebiasis, and tissue-invading amoebiasis. The bowel lumen infection, which is usually asymptomatic, may be in trophozoites form (non-infective) or in cysts form (infective); and treatment is directed at eradicating cysts with a luminal amoebicide (e.g. diloxanide). The tissue-invading amoebiasis (giving rise to dysentery, hepatic amoebiasis and liver abscess) must be treated with systemically active drugs (systemic amoebicides) active against trophozoites (e.g. metronidazole, tinidazole; also, in dangerously ill patients dehydroemetine may be used, which is less toxic than the parent emetine (derived from ipecacuanha). Sometimes antibiotics (e.g. tetracycline) are used concurrently to stop opportunist infections.