Many organic drugs that have been used to treat leishmaniasis and helminthic diseases have become ineffective today due to drug resistance.

The parasite Leishmania donovani, which is the cause of leishmaniasis, is transmitted to approximately 15 million people annually through the bite of a mosquito. This disease can be fatal if not treated, and its usual organic drugs such as pentamidine, amphotericin B, paromomycin and antimony drugs have become almost ineffective due to drug resistance.

With some of these compounds with metals, organometallic complexes have been made and evaluated for their anti-leishmaniasis activity. Pentamidine was one of these antiparasitic drugs that formed a complex with some metal centers and its activity has been investigated. In these investigations, it has been determined that one of the organic derivatives of osmium in combination with pentamidine shows 7.5 times more therapeutic effect than pentamidine in a single and similar dose in the treatment of leishmaniasis in mice.

Organic derivatives of iridium and platinum were tested against T. brucei in rodents, which treated infected mice with a single dose. An organic compound of iridium also showed anti-filariasis activity and showed a strong effect against the infectious larvae of Molinma destia and Borgia pahangi of human helminths parasites and a weak effect against leishmaniasis.

Iridium complex is significantly less toxic than pentamidine isothionate, so that its administration in lethal doses of pentamidine isothionate is allowed for this complex in rats. The organic derivative of iridium accumulates with pentamidine in Donovan flagella and binds with ribosomal subunits, but has no effect on macromolecular synthesis. It is clear that other organometallic complexes have a different mechanism, for example, osmium complexes inhibit the growth of Leishmania donovani by uniting amino acids and peptides as ligands indirectly and by preventing macromolecular synthesis.