Several antibiotics have been used to treat intestinal protozoal infections. Erythromycin and tetracycline do not have a direct effect on the protozoa; they act by al-tering intestinal bacterial flora and preventing second-ary infection. Tetracycline also reduces the normal gas-trointestinal bacterial flora on which the amebas depend for growth.
The aminoglycoside paromomycin (Humatin) has a mode of action identical to that of the other aminocycli-tols and is directly amebicidal. It is not absorbed from the intestinal tract and thus has its primary effect on bac-teria, some amebas (e.g., E. histolytica), and some helminths found in the lumen of the intestinal tract. Side effects are limited to diarrhea and gastrointestinal upset.
Amphotericin B, a polyene, it has produced healing of the mucocuta-neous lesions of American leishmaniasis, but its poten-tial for nephrotoxicity makes it a drug of second choice. On the other hand, liposomal amphotericin B, approved by the U. S. Food and Drug Administration (FDA) for treatment of visceral leishmaniasis, is considered the drug of choice for that indication and is much less toxic than pentavalent antimonials or amphotericin B.