By the end of this chapter, you should be able to:
Recognize parasitic infections and their key symptoms.
Identify prototype drugs for:
Amebicides (protozoa infections like giardiasis, amebiasis)
Antimalarials
Anthelmintics (worm killers)
Scabicides & Pediculicides (for lice/scabies)
Know MOA, use, adverse effects, contraindications, nursing implications for each prototype.
Apply the nursing process when caring for patients on these meds.
Parasite = lives off a host for nutrition, harming the host.
Can cause mild to life-threatening illness.
4 main types in this chapter:
Protozoa – Single-celled organisms (amebiasis, giardiasis, malaria, trichomoniasis)
Helminths – Worms (roundworms, hookworms, tapeworms)
Scabies – Mites burrowing in skin
Pediculosis – Lice on skin/hair
⚠ No vaccines exist for human parasites → we rely on prevention, insect control, and drug therapy.
Here’s your symptoms cheat sheet for each infection type:
Infection | Main Symptoms | Extra Key Points |
---|---|---|
Amebiasis | May be asymptomatic; or N/V/D, cramps, weakness. Severe: colon ulcerations, liver abscess. | Can be life-threatening if untreated. |
Giardiasis | May be asymptomatic; or diarrhea, cramps, distention, gas. Chronic: anorexia, weight loss, foul stools. | Vitamin B12, folate, fat-soluble vitamin deficiencies possible. |
Malaria | Fever, chills, headache, vomiting, flu-like. Untreated P. falciparum can be fatal in 24 hrs. | Attacks every 36–72 hrs; kids → severe anemia, cerebral malaria; adults → multi-organ failure. |
Trichomoniasis | Women: vaginal burning, itching, foul frothy yellow-gray discharge. Men: asymptomatic or urethritis. | Sexually transmitted. |
Helminthiasis | GI worms → cramps, diarrhea. Hookworm → anemia. Fish tapeworm → B12 deficiency. Pinworm → intense anal itching. | Larvae may travel to lungs → congestion. |
Scabies | Itchy burrows between fingers, wrists, elbows, under clothes areas. | Mite burrows visible. |
Pediculosis (lice) | Intense itching, allergic reaction to louse saliva. Scratching → skin infection. | Can be on scalp, body, or pubic area. |
Main groups of antiparasitics:
Amebicides – e.g., metronidazole
→ For protozoa like giardia, amebiasis.
Antimalarials – e.g., chloroquine
→ For malaria prevention/treatment.
Other antiprotozoals – For trichomoniasis.
Anthelmintics – For worms (mebendazole, albendazole).
Scabicides & Pediculicides – For mites & lice (permethrin, lindane).
Lacy Michelson – missionary, has giardiasis + malaria
At risk for: B12, folate, fat-soluble vitamin deficiencies (because giardia damages intestinal absorption).
Initial giardiasis symptoms: diarrhea, abdominal cramps/distention, gas.
Malaria with P. falciparum = emergency — must treat within 24 hrs to prevent death.
Hookworm = anemia from blood loss.
Fish tapeworm = B12 deficiency → megaloblastic anemia.
Giardia = foul-smelling stools + vitamin deficiencies.
Scabies & lice cause intense itching → risk for bacterial infection.
Pinworms cause perianal itching especially at night.
Purpose: Kill protozoa that cause amebiasis, giardiasis, and trichomoniasis.
Classification: Based on where they act:
Luminal amebicides → act in intestines (tetracycline, doxycycline)
Tissue/extraintestinal amebicides → act in bowel wall, liver, other tissues (chloroquine, metronidazole)
Absorption: ~80% orally absorbed; peak 1–3 hrs.
Distribution: Wide — CSF, bone, liver abscesses.
Half-life: 6–8 hrs.
Metabolism: Liver (30–60%).
Excretion: Urine (77%), feces (14%).
Diffuses into microorganism cell → causes cell death.
Exact biochemical pathway unknown.
Works against anaerobic protozoa & bacteria.
Intestinal amebiasis
Amebic liver abscess
Trichomoniasis
Bacterial vaginosis
Not FDA-approved for amebiasis prophylaxis.
For metronidazole & tinidazole:
Produced carcinogenic tumors in rats — only use for approved indications.
Pregnancy:
Crosses placenta.
1st trimester: ↑ risk of cleft lip/palate, congenital anomalies.
May use for giardiasis in 2nd or 3rd trimester.
CDC recommends for bacterial vaginosis in pregnant & nonpregnant.
Breastfeeding: Drug in breast milk same as plasma → hold breastfeeding 12–24 hrs after 2 g single dose.
Renal/hepatic impairment: Use caution — risk of drug accumulation.
Pediatrics: Dose by adjusted body weight if BMI ↑.
Condition | Adult Dose | Pediatric Dose |
---|---|---|
Amebiasis | 750 mg PO 5–10 days | 35–50 mg/kg/day PO ÷ TID × 7–10 days |
Giardiasis | 750 mg ER PO daily × 7 days | Weight-based |
Trichomoniasis | 2 g PO once OR 250 mg PO TID × 7 days | Weight-based |
CNS: Headache, dizziness, ataxia
GI: N/V/D, metallic taste
GU: Dark urine
Hypersensitivity: Rash, bronchospasm
Hypersensitivity to metronidazole.
Barbiturates: ↑ metabolism → ↓ effect.
Warfarin: ↑ bleeding risk (↓ vitamin K metabolism).
Alcohol/Alcohol-containing meds: Disulfiram-like reaction → tachycardia, flushing, nausea, vomiting.
Disulfiram + alcohol + metronidazole: severe reaction.
Preventing interactions
No alcohol during & 48 hrs after therapy.
Monitor INR if on warfarin.
Watch for drug accumulation in liver/kidney impairment.
Administering
Take with food to ↓ GI upset.
Do not crush ER tabs.
May crush regular tablets if patient can’t swallow.
Assessing for therapeutic effects
Amebiasis: ↓ abdominal pain, diarrhea, improved hydration, stools checked for cysts/trophozoites × 6 months.
Trichomoniasis: ↓ discharge, odor.
Assessing for adverse effects
Neuro changes (coordination loss, headache)
Metallic taste
Hypersensitivity (rash, bronchospasm)
Take full course.
Avoid alcohol → flushing, tachycardia, N/V.
Can cause metallic taste & dark urine (harmless).
Report rash, breathing problems, severe GI upset.
Women: Avoid sex during treatment for trichomoniasis; partners also need treatment.
Nitazoxanide (Alinia)
Inhibits parasite growth (sporozoites/oocysts in Cryptosporidium, trophozoites in Giardia).
Take with food.
Tinidazole
Similar to metronidazole.
CYP3A4 metabolism → caution in liver impairment.
AE: Bitter metallic taste, N/V.
Q: Patient with amebiasis takes metronidazole, then a cough syrup with alcohol. What effect?
A: Flushing (disulfiram-like reaction).
Q: What assessment shows therapy is working?
A: Diminished diarrhea.
Action of Metronidazole:
Diffuses into microorganism, disrupts cell function → cell death (exact biochemical process unknown).
Patient Education for Ms. Michelson:
Take full course exactly as prescribed.
Avoid alcohol during & for 48 hrs after therapy.
Expect metallic taste & dark urine.
Take with food to avoid stomach upset.
Report severe rash, breathing difficulty, dizziness, or persistent vomiting.
If pregnant or breastfeeding, discuss safety timing with provider.
Have follow-up stool checks for parasite clearance.
Purpose: Treat or prevent malaria by killing Plasmodium parasites at different life cycle stages.
Key Fact: No drug prevents infection, but they can suppress or cure symptoms and prevent recurrence.
Common Strategy: Combination therapy → reduces resistance risk.
Absorption: Rapid from GI tract.
Distribution: Wide — CNS, eyes, heart-lung system, liver, kidneys, spleen.
Peak: 1–2 hrs.
Half-life: 3–5 days (stays in body for months in urine).
Metabolism: Partial in liver.
Excretion: Kidneys.
Inhibits DNA & RNA polymerase → disrupts parasite metabolism.
Inhibits prostaglandins.
Raises parasite’s internal pH → stops growth.
Prevention (chemoprophylaxis) & treatment of malaria (P. malariae, P. ovale, P. vivax, P. falciparum — except resistant strains).
Extraintestinal amebiasis.
Often paired with primaquine for P. vivax & P. ovale to prevent relapse.
Crosses placenta, detected in newborns — but safe for prophylaxis in pregnancy.
Same dosing for pregnant & nonpregnant adults.
CNS: Visual disturbances, retinal damage, difficulty focusing.
CV: ECG changes (prolonged QRS), hypotension.
GI: N/V/D, ↓ appetite.
Skin/Hair: Rash, pruritus, hair loss.
Others: Ototoxicity, muscle weakness.
Allergy to 4-aminoquinoline compounds.
Existing retinal or visual field changes.
Caution: porphyria, psoriasis, retinal disease, G6PD deficiency, alcoholism, pregnancy, lactation.
↑ effect: Cimetidine.
↓ effect: Magnesium trisilicate, vitamin C (↑ urinary excretion).
Alcohol: ↑ GI distress.
Preventing interactions
Avoid antacids containing magnesium.
Avoid vitamin C-rich acidifying foods (cranberries, prunes, plums, cheeses, meats, fish, eggs, grains).
Administering
Prophylaxis: Same day each week.
Treatment: Same time each day; take with food to ↓ GI upset.
Children: Double-check doses — highly sensitive to toxicity.
Assessing therapeutic effects
Fever/chills ↓ in 24–48 hrs.
Blood smears negative in 24–72 hrs.
Assessing adverse effects
Eye changes (vision, focus).
ECG changes.
GI upset, rash, pruritus.
Complete full course.
Take with food.
For prevention: start 1–2 wks before travel, continue during stay, and 4 wks after leaving endemic area.
Eye exams every 3 months during therapy.
Avoid foods that acidify urine (cranberries, plums, prunes, cheese, meat, fish, eggs, grains).
Report vision changes, severe GI distress, rash.
Primaquine: Targets tissue forms (P. vivax/ovale). Screen for G6PD deficiency (risk hemolytic anemia).
Mefloquine: Prophylaxis/treatment for resistant strains. BBW — avoid in major psychiatric disorders; may cause neuropsychiatric effects even after stopping.
Artemether/lumefantrine (Coartem): WHO-approved for uncomplicated malaria. Avoid in QT prolongation. Take with food.
Atovaquone/proguanil (Malarone): Inhibits mitochondrial + folate pathway. Effective for resistant strains.
Hydroxychloroquine: Similar to chloroquine, fewer adverse effects; also used for lupus & RA.
Quinine: For resistant malaria, but more side effects.
Q: Which teaching is most important for chloroquine?
A: Have frequent ophthalmologic examinations.
Start chloroquine 1–2 weeks before travel, take same day each week, continue 4 weeks after leaving.
Take with food to avoid stomach upset.
Keep all eye exam appointments.
Avoid foods that acidify urine (cranberries, plums, prunes, cheeses, meats, fish, eggs, grains).
Report blurred vision, difficulty focusing, rash, itching, muscle weakness, hearing changes.
Do not skip doses — consistency prevents malaria symptoms.
Purpose: Kill or expel parasitic worms (helminths) from the body.
Two primary drug groups:
Ivermectin → strongyloidiasis, resistant lice.
Benzimidazoles → mebendazole (prototype), albendazole, triclabendazole.
Goal:
Eradicate parasite completely OR
Reduce worm burden so symptoms resolve.
Route: Oral.
Onset: Slow; peak 2–4 hrs.
Absorption: Only 2–10% absorbed — most stays in GI tract (great for intestinal worms).
Distribution: Highest in liver & muscle.
Protein binding: 95%.
Half-life: 3–6 hrs.
Metabolism: Liver (extensive).
Excretion: Mostly feces, small amount urine.
Blocks glucose uptake in helminths.
Depletes glycogen stores worms need for survival/reproduction → worm death.
FDA-approved:
Enterobius vermicularis (pinworm)
Trichuris trichiura (whipworm)
Ascaris lumbricoides (roundworm)
Ancylostoma duodenale & Necator americanus (hookworm)
Unlabeled:
Ancylostoma caninum (eosinophilic enterocolitis)
Capillaria philippinensis (capillariasis)
Giardia duodenalis
Mansonella perstans (filariasis)
Visceral larva migrans (toxocariasis)
Special note for pregnancy:
WHO recommends preventive therapy after 1st trimester in endemic areas.
First trimester: ↑ risk congenital anomalies.
Present in breast milk → caution while breastfeeding.
Condition | Adult Dose | Pediatric Dose |
---|---|---|
Trichuriasis, ascariasis, hookworm | 100 mg PO BID × 3 days | Same as adult if ≥2 yrs |
Enterobiasis | 1 tab PO once; repeat in 3 wks if not cured | Same as adult if ≥2 yrs |
CNS: Dizziness, drowsiness, headache, seizures.
GI: Abdominal pain, diarrhea, N/V.
Hematologic: Agranulocytosis, anemia, leukopenia, neutropenia.
Liver: ↑ AST & ALT (monitor for hepatic failure).
GU: Casts in urine, glomerulonephritis, hematuria.
Allergic: Rash, hypersensitivity, pulmonary reactions.
Hypersensitivity to mebendazole.
Increase mebendazole toxicity:
Metronidazole → ↑ risk of adverse effects.
Decrease mebendazole concentration:
Aminoquinolines (antimalarials)
Carbamazepine
Phenytoin ✅ (book “Success” answer)
Preventing Interactions
Avoid combining with interacting meds unless necessary.
Taking with food ↑ serum levels.
Administration
Chew & swallow OR crush and mix with food/liquid.
Can give with or without food, but food ↑ absorption.
Assessing therapeutic effects
Stool culture for ova & parasites 3 weeks after treatment.
Goal: Negative result + no worm burden.
Assessing adverse effects
Watch for:
CNS depression/seizures.
GI upset & dehydration signs.
Elevated liver enzymes.
Blood in urine / renal changes.
Rash, respiratory changes (hypersensitivity).
Good hygiene to prevent reinfection:
Wash hands, nails short & clean.
Wash bedding, underwear, clothes daily.
Treat all family members if pinworms present.
Complete entire course.
Return for follow-up stool test in 3 weeks.
Report fever, rash, breathing issues, seizures, severe GI upset.
Albendazole:
High-fat meal ↑ absorption (especially for systemic infection).
Same helminth coverage as mebendazole + cysticercosis & echinococcosis.
Triclabendazole (Egaten):
Used for fascioliasis (liver fluke infection).
Take with food; caution with QT-prolonging meds.
Ivermectin (Stromectol):
Best for Strongyloides stercoralis & resistant lice.
Usually well-tolerated; may cause mild N/V.
Q: Patient with enterobiasis on mebendazole — which agent ↓ serum concentration?
A: Phenytoin ✅
Purpose: Kill lice (Pediculosis capitis, pubis) and mites (Sarcoptes scabiei).
Prototype: Permethrin — first-line treatment for both lice & scabies.
Form: Topical cream/lotion.
Absorption: Minimal (~2%) through skin.
Metabolism: Liver (ester hydrolysis) → inactive metabolites.
Excretion: Urine.
Inhibits sodium ion influx through parasite nerve cell membranes → delays repolarization → paralysis & death of lice or scabies. ✅ (Correct answer to the book’s “Success” question)
Single application kills lice or scabies mites.
CDC recommends for pubic lice & scabies in pregnancy.
Can be used prophylactically during lice outbreaks.
Minimal systemic absorption → generally safe while breastfeeding.
Pruritus
Rash/erythema (especially scalp)
Burning, stinging, tingling, numbness, or pain at application site
Edema
Allergy to chrysanthemums, pyrethroid, or pyrethrin
Age < 2 months
Condition | How to Apply |
---|---|
Head lice | Apply to clean, damp hair & scalp — include behind ears & base of neck; leave 10 min; rinse; repeat in 1 week if lice/nits remain |
Scabies | Apply head-to-toe (include under nails, between fingers/toes, soles, genitals); leave 8–14 hrs; wash off; repeat in 1 week if mites appear |
Safety Alert:
Wear gloves to avoid spreading infestation to caregiver.
Follow product-specific directions.
Wash clothing, linens, towels daily during treatment.
Assess therapeutic effect:
Lice/nits or mites are dead/absent on recheck.
Itching may persist for days — does not mean treatment failure.
Assess adverse effects:
Local irritation, rash, burning, tingling, swelling.
Treat all close contacts to prevent reinfestation.
Wash bedding, towels, clothing in hot water & dry on high heat daily during treatment.
Avoid sharing hats, combs, brushes, towels.
Follow directions exactly — don’t leave on longer than prescribed.
Repeat treatment only if instructed.
Crotamiton (Crotan):
FDA-approved for scabies in adults; apply neck down.
Lindane:
Second-line; BBW — risk of seizures, neurotoxicity, death, especially in infants/children.
Avoid in premature infants, seizure disorders.
Malathion (Ovide):
For resistant head lice; flammable; leave 8–12 hrs.
Spinosad (Natroba):
Pediculicidal & ovicidal; causes parasite CNS excitation → paralysis & death; no systemic absorption.
Q: Action of permethrin?
A: Inhibits sodium influx through parasite nerve cell membranes → paralysis & death.