Anti protozoan Drugs
The number of anti protozoan drugs is relatively small, and the mechanism of action for most of these drugs is not completely understood. The drugs described here have potent anti protozoan action and appear to act on protozoan nucleic acid or some metabolic process.
Malaria, caused by any of five species of the genus Plasmodium, kills about a million people annually, most of them are children. Drugs to treat and prevent malaria include everything from ancient Chinese remedies to quinine water. In fact, gin and tonics are said to have been the most popular drink among imperial British in South Asia due to its antimalarial activity. We now use more purified forms of quinine drugs, including chloroquine and qualaquin to treat malaria.
How Drugs is working?
These drugs suppress protozoan reproduction and are effective in eradicating asexual stages of the protozoan’s life cycle that occur in red blood cells. Several mechanisms of action have been reported. They can raise the internal pH, clump the hemoglobin waste product hemazoin (often called the plasmodial pigment), and intercalate into plasmodial DNA. Chloroquine also inhibits malarial heme polymerase, an enzyme that converts toxic heme metabolites into the nontoxic hemazoin. Inhibition of this enzyme leads to a buildup of toxic heme metabolites.
Another drug, mefloquine, has been found to swell the Plasmodium falciparum food vacuoles, where it may act by forming toxic complexes that damage membranes and other plasmodial components. Primaquine is active against a dormant form of the protists (hypnozoites) that are found in the liver; it prevents relapses. Individuals who travel to areas where malaria is endemic typically receive chemoprophylactic treatment with chloroquine or other antimalarial agents.
Treatment of malaria
Treatment of malaria has become a complex task, with specific drugs and therapies recommended according to:
- The endemic Plasmodium species.
- Drug sensitivity and resistance patterns.
- Drug cost.
- Patient access to therapy.
Because of these factors, a single drug therapy may be recommended in one area, while a different drug or even a combination therapy may be recommended in another.
As mentioned, many factors impact treatment decisions, including patient compliance. Intermittent drug use is a strong selective pressure for drug resistance. Thus, treatment regimens may also rely on patient adherence to the drug dosing schedule. In general, the World Health Organization recommends a combination of a quinine drug and a derivative of artemisinin. Having its origins as a treatment in traditional Chinese medicine, artemisinin is a chemical found in the sweet wormwood plant (Artemisia annua).
A semisynthetic artemisinin derivative used in combination therapies is an effective treatment of malaria and a truly cost-effective treatment. The mechanism of artemisinin action is not well understood; it appears to form reactive oxygen intermediates inside Plasmodium-infected red blood cells, leading to altered hemoglobin catabolism and plasmodium electron transport chain damage.
Diseases caused by protozoa
There are many other diseases caused by protozoa, such as: Amoebic dysentery is usually treated with metronidazole. Anaerobic organisms, such as the causative agent Entamoeba, readily reduce it to the active metabolite within the cytoplasm. A number of antibiotics that inhibit bacterial protein synthesis are also used to treat protozoan infection. These include the aminoglycosides clindamycin and paromomycin.
Although aminoglycosides do not bind to eukaryotic ribosomes, these polycationic molecules have a high affinity for nucleic acids and RNA in particular. Different aminoglycoside antibiotics bind to different sites on RNAs. RNA binding interferes with the normal expression and function of the RNA, resulting in cell death.
The antifungal atovaquone (p.201) is used to treat toxoplasmosis, caused by Toxoplasma gondii. Toxoplasmosis is a lifethreatening infection in immuno compromised individuals and can cause severe birth defects in human fetuses. Atovaquone interferes with eukaryotic electron transport to kill the protozoan parasite.
Pyrimethamine and dapsone are also used to treat Toxoplasma infections and are thought to act in the same way as trimethoprim-interfering with folic acid synthesis by inhibition of dihydrofolate reductase. Another drug that interferes with electron transport is nitazoxanide, which is used to treat cryptosporidiosis, a food and waterborne disease .
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