In this article we will discuss about the antiamoebic and other antiprotozoal drugs.
Drug # 1. Emetine:
Emetine is an alkaloid obtained from Cephalis ipecacuanha. It is potent amoebicidal drug acting on trophozoites, but is no longer used, because of its cardiac toxicity.
Drug # 2. Meronidazole:
Metronidazole is the drug of first choice in treating amoebic infection of the bowel and abscess of the liver since it is very effective against vegetative forms of Entamoeba histolytica. A 5 day course is often sufficient (metronidazole is also used to treat the protozoan parasite Trichomonas vaginalis and Giardia lamblia and anaerobic infections).
Vomiting can be troublesome at the dose levels used to treat amoebic dysentery. Metronidazole can be combined with diloxanide furoate, which is active against organisms in the bowel lumen, but not in the tissues. The combination appears to be even more efficient in eradicating the infection.
Drug # 3. Tinidazole:
Tinidazole has similar pharmacological properties as that of metronidazole, but is better tolerated and has a longer duration of action and given once daily. It is available only for oral use.
Drug # 4. Diloxanide Furoate:
Diloxanide furoate is effective against the non-invasive vegetative forms (trophozoites) of E. histolytica in the intestinal lumen. It has no effect on amoebic ulcers or in systemic amoebiasis.
It directly kills trophozoites, responsible for cyst formation. It has no antibacterial action. It is partly absorbed, metabolized in the liver and excreted in the urine within 48 hours.
Diloxanide furoate is given orally in doses of 500 mg every 8 hours for 10 days in combination with metronidazole or tinidazole for eradication of amoebic infection.
Diloxanide furoate is relatively free from toxic effects. Flatulence, vomiting, urticaria and pruritus may occur.
Drug # 5. Chloroquine:
Chloroquine, an antimalarial, has little effect on intestinal amoebiasis, but is highly effective in amoebic liver absces. It is used only in those cases of hepatic amoebiasis, which fail to respond to metronidazole.
Drug # 6. Halogenated Hydroxyquinolines:
Iodochlorohydroxyquin and diiodohydroxyquin have direct amoebicidal action on luminal parasites, but like diloxanide furoate are not useful in hepatic amoebiasis. Prolonged use of iodochlorohydroxyquin has been associated with serious immunological disorder, subacute myelooptic neuropathy (SMON) characterised by polyneuritis and optic atrophy. The drug has been withdrawn from Japan and western countries. Diiodohydroxyquin is still available in India and may be used an alternative to diloxanide furoate, but offers no advantage.
Drug # 7. Leishmaniasis:
Visceral leishmaniasis (kala azar) is endemic in the eastern states of India. There are several varieties of kala azar caused by closely related organisms, due to the bite of female sand fly, Phlebotomus. These organisms invade spleen, liver, lymph glands and bone marrow, producing a generalized disease with constitutional symptoms or produce a local ulcerative lesion. It may complicate HIV infection. Cutaneous leishmaniasis frequently heals spontaneously.
Drug # 8. Sodium Stibogluconate:
Sodium stibogluconate, an organic pentavalent antimony compound, is the drug of choice for kala azar. It is believed to act by interfering with enzymes within the parasites. It is given in a dose of 20 mg/kg by intramuscular or slow intravenous injection for at least 20 days. Sometimes, it may be necessary to repeat courses at intervals of 2 weeks. Side effects are GIT disorders, cardio-toxicity and rarely anaphylaxis. Injections are painful and carry a risk of thrombosis. It is contraindicated in renal impairment and breast-feeding.
Drug # 9. Amphotericin B:
Amphotericin B, an antifungal antibiotic, is used with or after antimony compound for visceral leishmaniasis, unresponsive to antimony compound alone.
Drug # 10. Paromomycin:
Paromomycin, an antibiotic, is also effective either alone or combined with antimony compound. Side effects are uncommon, but include ototoxicity.
Drug # 11. Pentamidine:
Pentamidine, a drug used for Pneumocystis pneumonia (commonest cause of pneumonia in AIDS), has been used in antimony resistant visceral leishmaniasis, but relapses are common. It is given by intravenous injection.
Pentamidine is concentrated in liver and kidney and is excreted slowly unchanged by kidneys. It is highly toxic drug and may cause anaphylaxis, kidney, liver and cardiac damage.