Emetine amoebicidal activity

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. 

The antidiarrhoeal drug ipecac, which was introduced into Europe from Brazil in 1658, contains the amoebicidal alkaloids emetine (12) and cephaeline. Emetine remained the major remedy for amoebic dysentery and amoebic hepatitis for many years. Cephaeline is less active and more toxic. ( j-2-Dehydroemetine, which is made by synthesis, is equiactive with (—)-emetine and less toxic, but other chemical modification has not yielded better amoebicides. From investigations of synthetic routes to the benzoquinolizine moiety the tranquilizer tetrabenazine (13a) was discovered. The very similar compound benzquinamide (13b) is also a tranquilizer and antiemetic. 

Q. is used in the food industry as a bitter principle, according to legal regulations brandies may contain up to 50 mg/L Q. as bitter component. Q. has a bitter taste even at a dilution of 1 60 000. In mammals Q. can effect a decrease in heart rate and, at higher concentrations, muscular convulsions and paralyses. The commercially available quassin is a mixture of quassin, neoquassin, isoquassin, and 18-hydroxy-quassin. Q. can be used as a substitute for emetine hydrochloride (see ipecac alkaloids). Some pentacyclic Q. have antiviral, antiparasitic, insecticidal, antifeedant, amoebicidic, and anti-inflammatory activities. 

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