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To simplify the discussion, the antimalarial drugs are covered in a separate section at the end of this chapter. Some of the more common protozoal diseases are listed in the following table.
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Of the drugs that are used in these diseases, metronidazole is the one that is the most important for you to know. Of the diseases listed, trichomoniasis and giardiasis are the most common in the United States and both are treated with metronidazole. This along with a few more details will go a long way. You need to be aware of the other drugs and where to find the information about treatment for these diseases.
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METRONIDAZOLE is effective in the treatment of vaginal trichomoniasis, giardiasis, and all forms of amebiasis.
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First note that metronidazole, fenbendazole, and tinidazole end in “azole,” but are not anti-fungal agents. Sorry!
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Metronidazole is one of the most effective drugs against anaerobic bacteria and several protozoal species. It is highly effective in the treatment of trichomoniasis. It penetrates protozoal and bacterial cell walls, but cannot enter mammalian cells. The drug must be activated once it has entered the cell. The activating enzyme, nitroreductase, is only found in anaerobic organisms. The reduced metronidazole inhibits DNA replication by causing breaks and inhibiting repair of the DNA.
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The most common side effects are nausea, vomiting, and diarrhea. The drug can turn the urine dark or red-brown and cause a metallic taste in the mouth. Metronidazole can cause a disulfiram-like reaction when taken with alcohol. The disulfiram-like effect consists of abdominal cramping, vomiting, flushing, or headache after drinking alcohol.
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Malaria is caused by a single-cell protozoa, the plasmodium. There are over 50 species of plasmodia, but only four are infectious to humans: Plasmodium malariae, Plasmodium ovale, Plasmodium vivax, and Plasmodium falciparum. Plasmodium vivax is the most prevalent, but P. falciparum is the most serious and lethal form of malaria.
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To understand the drugs and the rationale behind treatment of patients with malaria, it is important to understand the life cycle of the malaria organism (Figure 34–1).
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