Protozoa are single-celled organisms that can infect humans and cause diseases such as amoebiasis, giardiasis, sleeping sickness, and leishmaniasis. Anti-protozoal agents are medicines used to treat these infections by killing the protozoa or stopping their growth.
Symptoms of Amoebiasis
Amoebiasis is one of the most common protozoal infections. It is caused by Entamoeba histolytica. The major symptoms include:
- Abdominal pain and cramps
- Loose stools or diarrhea
- Presence of blood or mucus in stool
- Weakness, tiredness and dehydration in severe cases
Approaches to Protozoal Therapy
Anti-protozoal treatment depends on the type and stage of infection. The main approaches include:
- Tissue amoebicides: Drugs that act inside tissues, used when the infection spreads beyond the intestine.
- Luminal amoebicides: Act inside the intestine to eliminate cysts and prevent reinfection.
- Mixed amoebicides: Drugs that work both in tissues and the intestine.
Anti-Protozoal Agents: Major Drugs
1) Metronidazole
Metronidazole is one of the most widely used anti-protozoal drugs. It is effective against intestinal and extraintestinal amoebiasis.
Mechanism: Inside protozoal cells, the drug is reduced to active metabolites that damage DNA and halt protein synthesis, ultimately killing the organism.
2) Tinidazole
Tinidazole works similarly to metronidazole but has a longer duration of action and is often given as a once-daily dose.
Uses: Amoebiasis, giardiasis, and trichomoniasis.
3) Ornidazole
Ornidazole also belongs to the nitroimidazole class. It is better tolerated, causes fewer side effects, and is effective in treating both intestinal and liver amoebiasis.
4) Diloxanide
Diloxanide is a luminal amoebicide. It is not absorbed completely, so it remains inside the intestine to eliminate cyst forms of amoeba.
Use: Asymptomatic carriers of amoebiasis and to prevent recurrence of infection.
5) Iodoquinol
Iodoquinol is another luminal agent used to treat mild intestinal amoebiasis. It acts locally in the bowel and is often combined with metronidazole for better results.
6) Pentamidine Isethionate
Pentamidine is used to treat protozoal diseases such as:
- African sleeping sickness
- Leishmaniasis
- Pneumocystis infections
Mechanism: It interferes with nucleic acid and protein synthesis in protozoa.
7) Atovaquone
Atovaquone is an anti-protozoal drug used for Pneumocystis pneumonia, malaria, and toxoplasmosis (often in combination therapy).
Mechanism: It blocks the mitochondrial electron transport chain necessary for protozoal survival.
8) Eflornithine
Eflornithine is used mainly for treating African sleeping sickness.
Mechanism: It inhibits an enzyme needed for protozoal cell division, stopping parasite growth.
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