Antiprotozoal drugs

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Protozoan infections are a group of the diseases caused by unicellular organisms. The most common protozoa diseases include: Giardiasis, Trichomoniasis, Leishmaniasis, Amebiasis, Malaria. Protozoal infections are especially common for poorly developed tropical or subtropical countries where hygiene and sanitatory conditions are inappropriate. Protozoa are eukaryotic unicellular organisms. The structure and metabolism of eukaryotic cells are very close to those in human host. Therefore, protozoal infections are hardly treated and have a high rate of toxicity. Evolution has developed in mammals many efficient protective mechanisms to deal with protozoa and other invading parasites. However, many of parasites developed their own tactics to escape the defensive responses of the host. Some of the parasites penetrate human host cells where antibodies are not able to reach them. For example, Plasmodia species take refuge in erythrocytes (red blood cells), Leishmania species affect macrophages exclusively, Trypanosome species invade a lot of cell types. Malaria is a group of transmissive infectious diseases affecting humans after bites of malarial mosquitos Anopheles and accompanied by fever, splenomegaly, hepatomegaly, anemia. Malaria is characterized by chronic recurrent flow of the disease and is caused by various species of Plasmodia.

Malaria treatment include the following approaches:
First approach:

  • Medicines used for acute malarial infections include: quinine, doxycycline, mefloquine, chloroquine, alofantrine, sulfones, pyrimethamine, tetracycline.
  • Medicines used for malaria prophylaxis: chloroquine, mefloquine, proguanil, pyrimethamine, dapsone, doxycycline

Second approach:

  • Medicines used for radical cure: primaquine that is active against liver parasites.
  • Medicines acting on gametocytes and prevent transmission

by the mosquito
(primaquine, proguanil, pyrimethamine)

Amebiasis is anthropogenic invasion with fecal-oral route of infection transmission that is characterized by chronic recurrent colitis with extraintestinal manifestations. Amebiasis is caused by Entamoebahistolytica that causes dysentery associated with invasion of the bowel's wall and, in rare cases of the liver. Entamoeba can exist in the motile, invasive or in the form of cyst. First line amebiasis treatment includes metronidazole that is effective against the invading forms in the liver and gut. Tinidazole, Ornidazole, Nimorazole are also indicated against Amebiasis. Second line amebiasis treatment includes: Diloxanidine (used for non-invasive forms), Iodoquinol, Paromomycin (effective against intestinal invasion), Emetine and Chloroquine are effective against extraintestinal amebiasis.

Leishmaniasis is a group of parasitic ,zoonotic, transmissive diseases found in tropical and subtropical countries and is caused by parasitic protozoa genus Leishmania, which are transmitted to humans through mosquito bites. There are two main forms of the disease: visceral leishmaniasis, or kala-azar, which affects the organs of the reticulo-endothelial system and cutaneous leishmaniasis, which affects the skin and subcutaneous tissue. Three clinical types of leishmaniasis include:

  • Simple skin infection
  • Mucocutaneous form
  • Visceral form

First line treatment of visceral leishmaniasis include sodium stibogluconate and meglumine antimoniate, but resistance to these agents are increasing. Pentamidine isethionate is used in resistant cases.

Other anti-leishmanial drugs include: amphotericin, metronidazole, paromomycin, some antifungal azoles and allopurinol.

Trypanosomiasis is protozoal infection caused by T. gambiense, and T. rhodesiense that causes sleeping sickness and T. cruzi causes Chagas' disease. In both types of disease there is an initial local lesion at the site of entry, followed by bouts of parasitemia and fever. Organs damage is caused by the toxins affecting CNS, heart, spleen, liver, bowel and bones. First line treatment of sleeping sickness includes suramin with pentamidine, and melarsoprol for the late stage of the disease.

Trichomoniasis is a sexually transmitted infection caused by protozoan parasite Trichomonas vaginalis. Usually, only women experience symptoms of Trichomonas infection. Symptoms include inflammation of the cervix (cervicitis), urethra (urethritis), and vagina (vaginitis) which produce an itching or burning sensation. Trichomonas infection is treated by Primaquine, puromycin, nifurtimox, benznidazole and metronidazole.

Toxoplasmosis is parasitic disease of humans and animals caused by Toxoplasma. The source of infection are different types (over 180) of domestic and wild mammals (cats, rabbits, carnivores, herbivores, rodents, etc.) and birds. Acute form of toxoplasmosis is characterized by fever, splenomegaly, hepatomegaly and damage of nervous system (headache, seizures, vomiting). Toxoplasmosis is treated by pyrimethamine in combination with a sulfonamide. Also pentamidine and azithromycin are indicated.

Giardiasis is an infection of the small intestine caused by a microscopic organism (protozoa), Giardia lamblia. The most common symptom of the infection is vomiting, diarrhea, meteorism, loss of appetite, nausea, swollen abdomen, low-grade fever. Giardiasis is treated by mentronidazole, tinidazole, nitazoxanidine.