Antiprotozoal Drugs

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Antiprotozoal Drugs


Antiprotozoal drugs are medicines that treat infections caused by protozoa.


Antiprotozoal drugs are used to treat a variety of diseases caused by protozoa. Protozoa are animal-like, one-celled animals, such as amoebas. Some are parasites that cause infections in the body. African sleeping sickness, giardiasis, amebiasis, Pneumocystis carinii pneumonia (PCP), and malaria are examples of diseases caused by protozoa.


Antiprotozoal drugs come in liquid, tablet, and injectable forms and are available only with a doctor's prescription. Some commonly used antiprotozoal drugs are metronidazole (Flagyl), eflornithine (Ornidyl), furazolidone (Furoxone), hydroxychloroquine (Plaquenil), iodoquinol (Diquinol, Yodoquinol, Yodoxin), and pentamidine (Pentam 300).

Recommended dosage

The recommended dosage depends on the type of antiprotozoal drug, its strength, and the medical problem for which it is being used. Check with the physician who prescribed the drug or the pharmacist who filled the prescription for the correct dosage. Always take antiprotozoal drugs exactly as directed.


Some people feel dizzy, confused, lightheaded, or less alert when using these drugs. The drugs may also cause blurred vision and other vision problems. For these reasons, anyone who takes these drugs should not drive, use machines or do anything else that might be dangerous until they have found out how the drugs affect them.

The antiprotozoal drug furazolidone may cause very dangerous side effects when taken with certain foods or beverages. Likewise, metronidazole (Flagyl) can cause serious liver damage if taken with alcohol. Check with the physician who prescribed the drug or the pharmacist who filled the prescription for a list of products to avoid while taking these medicines.

Anyone who has ever had unusual reactions to antiprotozoal drugs or related medicines should let his or her physician know before taking the drugs again. The physician should also be told about any allergies to foods, dyes, preservatives, or other substances.

Some antiprotozoal drugs may cause problems with the blood. This can increase the risk of infection or excessive bleeding. Patients taking these drugs shouldbe careful not to injure their gums when brushing or flossing their teeth or using a toothpick. They shouldcheck with the physician before having any dentalwork done. Care should also be taken to avoidcuts from razors, nail clippers, or kitchen knives, orhousehold tools. Anyone who has any of these symptoms while taking antiprotozoal drugs should call the physician immediately:

  • Fever or chills
  • Signs of cold or flu
  • Signs of infection, such as redness, swelling, or inflammation
  • Unusual bruising or bleeding
  • Black, tarry stools
  • Blood in urine or stools
  • Pinpoint red spots on the skin
  • Unusual tiredness or weakness.

Anyone taking this medicine should also check with a physician immediately if any of these symptoms occur:

  • Blurred vision or other vision changes
  • Skin rash, hives, or itching
  • Swelling of the neck
  • Clumsiness or unsteadiness
  • Numbness, tingling, pain, or weakness in the hands or feet
  • Decrease in urination.

Children are especially sensitive to the effects of some antiprotozoal drugs. Never give this medicine to a child unless directed to do so by a physician, and always keep this medicine out of the reach of children. Use safety vials.

The effects of antiprotozoal drugs on pregnant women have not been studied. However, in experiments with pregnant laboratory animals, some antiprotozoal drugs cause birth defects or death of the fetus. Women who are pregnant or who plan to become pregnant should check with their physicians before taking antiprotozoal drugs. Mothers who are breastfeeding should also check with their physicians about the safety of taking these drugs.


Amebiasis An infection caused by an ameba, which is a type of protozoan.

Fetus A developing baby inside the womb.

Giardiasis A condition in which the intestines are infected with Giardia lamblia, a type of protozoan.

Inflammation Pain, redness, swelling, and heat that usually develop in response to injury or illness.

Parasite An organism that lives and feeds in or on another organism (the host) and does nothing to benefit the host.

Pneumocystis carinii pneumonia A severe lung infection caused by a parasitic protozoan. The disease mainly affects people with weakened immune systems, such as people with AIDS.

Before using antiprotozoal drugs, people with any of these medical problems should make sure their physicians are aware of their conditions:

  • Anemia or other blood problems
  • Kidney disease
  • Heart disease
  • Low blood pressure
  • Diabetes
  • Hypoglycemia (low blood sugar)
  • Liver disease
  • Stomach or intestinal disease
  • Nerve or brain disease or disorder, including convulsions (seizures)
  • Psoriasis (a skin condition)
  • Hearing loss
  • Deficiency of the enzyme glucose-6-phosphate dehydrogenase (G6PD)
  • Eye or vision problems
  • Thyroid disease.

Side effects

The most common side effects are diarrhea, nausea, vomiting, and stomach pain. These problems usually go away as the body adjusts to the drug and do not require medical treatment.

Other rare side effects may occur. Anyone who has unusual symptoms after taking an antiprotozoal drug should get in touch with his or her physician.


Antiprotozoal drugs may interact with other medicines. When this happens, the effects of one or both of the drugs may change or the risk of side effects may be greater. Anyone who takes antiprotozoal drugs should let the physician know all other medicines he or she is taking. Among the drugs that may interact with antiprotozoal drugs are:

  • Alcohol
  • Anticancer drugs
  • Medicine for overactive thyroid
  • Antiviral drugs such as zidovudine (Retrovir)
  • Antibiotics
  • Medicine used to relieve pain or inflammation
  • Amphetamine
  • Diet pills (appetite suppressants)
  • Monoamine oxidase inhibitors (MAO inhibitors) such as phenelzine (Nardil) and tranylcypromine (Parnate), used to treat conditions including depression and Parkinson's disease.
  • Tricyclic antidepressants such as amitriptyline (Elavil) and imipramine (Tofranil)
  • Decongestants such as phenylephrine (Neo-Synephrine) and pseudoephedrine (Sudafed)
  • Other antiprotozoal drugs.

The list above does not include every medicine that may interact with an antifungal drug. Be sure to check with a physician or pharmacist before combining antifungal drugs with any other prescription or nonprescription (over-the-counter) medicine.