effective in severe and multidrug resistant malaria. They are well tolerated but should be used with caution in patients with chronic cardiac disorders as they prolong the PR and QT interval in some experimental animals. Their place in therapy is being evaluated.

Infection occurs when mature cysts are ingested and pass into the colon where they divide into trophozoites; these forms either enter the tissues or reform cysts. Amoebiasis occurs in two forms, both of which need treatment:

• Bowel lumen amoebiasis is asymptomatic and trophozoites (noninfective) and cysts (infective) are passed into the faeces. Treatment is directed at eradicating cysts with a luminal amoebicide; diloxanide furoate is the drug of choice; iodoquinol or paromomycin is sometimes used.

• Tissue-invading amoebiasis gives rise to dysentery, hepatic amoebiasis and liver abscess. A systemically active drug (tissue amoebicide) effective against trophozoites must be used, e.g. metronidazole, Imidazole. Parenteral forms of these are available for patients too ill to take drugs by mouth. In severe cases of amoebic dysentery, tetracycline lessens the risk of opportunistic infection, perforation and peritonitis when it is given in addition to the systemic amoebicide.

Treatment with tissue amoebicides should always be followed by a course of a luminal amoebicide to eradicate the source of the infection.

Dehydroemetine (from ipecacuanha), less toxic than the parent emetine, is claimed by some authorities to be the most effective tissue amoebicide. It is reserved for dangerously ill patients, but these are more likely to be vulnerable to its cardiotoxic effects. When dehydroemetine is used to treat amoebic liver abscess, chloroquine should also be given.

The drug treatment of other protozoal infections is summarised in Table 14.4.

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