Few of the antibacterial antibiotics work against protozoa or helminths.
Amphotericin inhibits the production of ergosterol, which is the major sterol of cell membranes of the yeast stages of fungi and the amastigote stages of leishmania. Conventional preparations are too toxic for routine use, as a first choice. The liposomal preparations are more efficient and less toxic but extremely expensive. Ivermectin is an antibiotic widely used against helminths in veterinary medicine and is valuable in human filarial infections.
Many antiparasitic drugs are derived from traditional remedies (quinine comes from cinchona bark), ancient pharmacopoeias (stibogluconate and melarsen B contain toxic heavy metals), or from random screening (mepacrine and chloroquine). Recently, the pharmaceutical industry has taken a more serious interest in tropical parasitic infections and logical derivatives are being developed. Among the most useful are those based on the imidazole ring. The nitroimidazoles, metronidazole and tinidazole, are effective against intestinal protozoa, as well as anaerobic bacteria, while the benzimidazoles, such as mebendazole and albendazole, are effective against a wide range of helminthic infections. Other azoles such as ketoconazole inhibit enzymes in the ergosterol pathway and have some action against leishmania as well as fungi. Praziquantel is an important agent in the management of schistosome infection. Atovaquone, a hydroxynaphthoquinone, has been developed as an antimalarial and is marketed in combination with proguanil.
The indications and dosages are given in individual sections dealing with specific infections.