Antiprotozoal Drugs Nursing Pharmacology Study Guide

Antiprotozoal Drugs: Generic and Brand Names

• Antimalarials
  • chloroquine (Aralen)
  • mefloquine (Lariam)
  • primaquine
  • pyrimethamine (Daraprim)
  • quinine (Qualaquin)
• Other antiprotozoals
  • atovaquone (Mepron)
  • metronidazole (Flagyl)
  • nitazoxanide (Alinia)
  • pentamidine (Pentam 300)
  • tinidazole (Tindamax)

Disease Spotlight: Protozoal Diseases

Malaria. A cycle of fever and chills transmitted by the bite of a female Anopheles mosquito. Known causes include Plasmodium falciparum, vivax, malariae, and ovale. Sporozoites travel through the bloodstream and lodge in the liver and other tissues. Malaria is endemic in many parts of the world.

Amebiasis. An intestinal infection caused by Entamoeba histolytica, often called amoebic dysentery, transmitted by the fecal-oral route. It runs from mild to fulminant diarrhea and in the worst cases invades extraintestinal tissue.

Leishmaniasis. Caused by a protozoan passed from sand flies to humans. Marked by serious lesions in the skin, viscera, and mucous membranes.

Trypanosomiasis. Caused by Trypanosoma, leading to African sleeping sickness and Chagas' disease. African sleeping sickness comes from T. brucei gambiense, transmitted by the tsetse fly, and presents with lethargy, prolonged sleep, and even death. Chagas' disease comes from T. cruzi, passed to humans by the common housefly, and causes severe cardiomyopathy.

Trichomoniasis. Caused by T. vaginalis, a common cause of vaginitis (reddened, inflamed vaginal mucosa, itching, burning, yellowish-green discharge). Usually transmitted through sexual intercourse. Asymptomatic in men.

Giardiasis. Caused by G. lamblia, the most commonly diagnosed intestinal parasite in the United States. Transmitted through contaminated water or food and trophozoites. Presents with diarrhea; rotten-egg-smelling, pale, mucus-filled stool; and sometimes epigastric pain, weight loss, and malnutrition.

Antimalarials

Antimalarials attack Plasmodium at various stages of its life cycle, which is how they prevent acute malarial reaction in an infected patient. They can be schizonticidal (acting on the red-blood-cell phase), gametocytocidal (acting on gametocytes), sporontocidal (acting on parasites developing in the mosquito), or work against tissue schizonts as a prophylactic or antirelapse agent. Quinine (Qualaquin) was the first drug found effective against malaria.

Therapeutic Action

Antimalarials enter human red blood cells and change the metabolic pathways the parasite needs to reproduce. Chloroquine, the mainstay of treatment, is also directly toxic to parasites and reduces their ability to synthesize DNA.

Indications

Treatment of malaria, prevention of relapse, and other protozoal diseases such as extraintestinal amoebiasis (chloroquine) and toxoplasmosis (pyrimethamine).

Age-group points worth remembering:

• Children are very sensitive to most antiprotozoals, so expect more severe reactions. Many lack proven safety and efficacy data in children.
• Adults need clear advice about prophylaxis and the need for immediate treatment if disease is contracted. Use during pregnancy and lactation is justified only when benefits clearly outweigh the risk. Women of childbearing age should use barrier contraceptives while on any antiprotozoal.
• Older adults are more susceptible to adverse effects, especially with hepatic and renal dysfunction.

Pharmacokinetics

Here are the characteristic interactions of antimalarials and the body in terms of absorption, distribution, metabolism, and excretion:

Contraindications and Cautions

• Known allergy to the drug. Prevents hypersensitivity reactions.
• Liver disease or alcoholism. Parasites invade the liver and the drugs need hepatic metabolism; protect against toxicity.
• Lactation. Drugs enter breast milk and can be toxic to the infant.
• Pregnancy. Associated with birth defects. Avoid pregnancy for 2 months after completing mefloquine therapy.
• Retinal disease or damage. Drugs can affect vision and the retina, and problems are more likely if the retina is already damaged.
• Psoriasis or porphyria. Skin damage from drug effects on proteins and protein synthesis.

Adverse Effects

• CNS: headache, dizziness
• Immunological: fever, shaking, chills, malaise
• GI: nausea, vomiting, dyspepsia, anorexia, hepatic dysfunction
• Dermatological: rash, pruritus, hair loss tied to changes in protein synthesis
• Eyes: visual changes, possible blindness
• Ears: ototoxicity from nerve damage
• Cinchonism (nausea, vomiting, tinnitus, vertigo) can occur with high levels of quinine or primaquine.

Interactions

• Quinine and quinine derivatives: increased risk of cardiac toxicity and convulsions.
• Anti-folate drugs (methotrexate, sulfonamides): increased bone marrow suppression with pyrimethamine. Stop pyrimethamine if signs of folate deficiency develop (diarrhea, fatigue, weight loss, anemia).

Nursing Considerations

Assessment. Screen for the cautions and contraindications above (drug allergies, hepatorenal impairment, pregnancy and lactation, visual disturbances). Do a full physical for baseline data, and add ophthalmic, retinal, and auditory screening since these drugs threaten vision and hearing. Check liver function, including LFTs, to gauge appropriateness and watch for toxicity. Draw a blood culture to identify the causative Plasmodium species.

Nursing diagnoses. Acute pain related to GI, CNS, and skin effects; disturbed sensory perception (kinesthetic, visual) related to CNS effects; risk for injury related to CNS changes.

Interventions. Arrange culture and sensitivity testing before starting to match the drug to the susceptible Plasmodium species. Give the complete course for full effect. Monitor hepatic function and repeat ophthalmologic exams before and during treatment, and stop the drug at signs of liver failure or deteriorating vision. Provide comfort and safety measures for CNS effects (side rails, ambulation assistance for dizziness or weakness), and oral hygiene plus bathroom access for GI effects. Teach the patient to promote understanding and compliance.

Evaluation. Monitor response (resolution or prevention of malaria) and adverse effects (orientation and affect, nutrition, skin, hepatic function, visual and auditory changes). Confirm the patient can name the drug, its indication, and the adverse effects to watch for, and check compliance.

Other Antiprotozoal Agents

Therapeutic Action

These agents inhibit DNA synthesis in susceptible protozoa, blocking the cell's ability to reproduce and leading to cell death.

Indications

Treatment of infections caused by susceptible protozoa.

Pharmacokinetics

Here are the characteristic interactions of other antiprotozoal agents and the body in terms of absorption, distribution, metabolism, and excretion:

Contraindications and Cautions

• Known allergy to the drug. Prevents hypersensitivity reactions.
• Pregnancy. Effects on developing fetal DNA and proteins can cause fetal abnormalities and death.
• CNS disease. Possible exacerbation from drug effects on the CNS.
• Hepatic disease. Possible exacerbation from hepatic drug effects.
• Candidiasis. Risk of superinfection.
• Lactation. Drugs pass into breast milk and can cause severe adverse effects in the infant.
• Tinidazole should never be combined with alcohol.

Adverse Effects

• CNS: headache, dizziness, ataxia, loss of coordination, peripheral neuropathy
• GI: nausea, vomiting, diarrhea, unpleasant taste, cramps, changes in liver function
• Superinfections

Interactions

• Alcohol: severe adverse effects with tinidazole and metronidazole. Avoid alcohol for at least 3 days after treatment.
• Oral anticoagulants: increased bleeding with metronidazole and tinidazole.
• Disulfiram: increased psychotic reactions with metronidazole and tinidazole. Allow 2 weeks between tinidazole therapy and starting disulfiram.

Nursing Considerations

Assessment. Screen for the cautions and contraindications above (drug allergies, hepatorenal impairment, pregnancy and lactation). Do a full physical for baseline data, check liver function and LFTs, and obtain cultures to pin down the protozoal species.

Nursing diagnoses. Acute pain related to GI and CNS effects; imbalanced nutrition: less than body requirements related to severe GI effects; disturbed sensory perception (kinesthetic, visual) related to CNS effects.

Interventions. Arrange culture and sensitivity testing before starting. Give the complete course. Monitor hepatic function before and during treatment and stop the drug at signs of liver failure. Provide comfort and safety measures for CNS effects (side rails, ambulation assistance), and oral hygiene plus bathroom access for GI effects. Teach the patient.

Evaluation. Monitor response (resolution of infection and negative parasite cultures) and adverse effects (orientation and affect, nutrition, skin, hepatic function, superinfections). Confirm the patient can name the drug, its indication, and adverse effects, and check compliance.

Frequently Asked Questions

How do antimalarials kill the parasite? Chloroquine, the most widely used 4-aminoquinoline, concentrates inside the parasite's digestive vacuole and raises its pH, which interferes with the parasite's ability to metabolize and use erythrocyte hemoglobin. It acts as a blood schizonticide against the red-blood-cell stage (StatPearls).

How does metronidazole work against protozoa? Inside the organism, metronidazole is reduced into reactive intermediates that bind the parasite's DNA, disrupting it and shutting down protein synthesis. It treats amebiasis, giardiasis, and trichomoniasis (StatPearls).

Why must patients on metronidazole or tinidazole avoid alcohol? The combination can cause a disulfiram-like reaction (flushing, nausea, vomiting, cramping). Patients should avoid alcohol during therapy and for at least three days after the last dose.

Why take a travel and living-conditions history? Protozoal infections are tied to tropical travel and to crowded or unsanitary conditions, and species like Giardia spread through contaminated water or food. Exposure history helps target which protozoan to look for and which drug to choose.

Why obtain cultures before starting treatment? Different protozoa respond to different agents, so identifying the species (for malaria, the specific Plasmodium) lets you match the drug to the infection and avoid an ineffective course.

What monitoring matters most with long-term antimalarials? These drugs can damage the retina and affect hearing, so baseline and periodic ophthalmologic exams are standard, along with liver function testing. Stop the drug at any sign of vision change or liver failure.