TS

Chapter 25- Parasitic infections

Introduction

🎯 Learning Objectives – What You NEED to Know Cold

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.


🧬 Big Picture: What’s a Parasite?

  • Parasite = lives off a host for nutrition, harming the host.

  • Can cause mild to life-threatening illness.

  • 4 main types in this chapter:

    1. Protozoa – Single-celled organisms (amebiasis, giardiasis, malaria, trichomoniasis)

    2. Helminths – Worms (roundworms, hookworms, tapeworms)

    3. Scabies – Mites burrowing in skin

    4. Pediculosis – Lice on skin/hair

No vaccines exist for human parasites → we rely on prevention, insect control, and drug therapy.


🩺 Clinical Manifestations (Know These!)

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.


💊 Drug Therapy Overview

Main groups of antiparasitics:

  1. Amebicides – e.g., metronidazole
    → For protozoa like giardia, amebiasis.

  2. Antimalarials – e.g., chloroquine
    → For malaria prevention/treatment.

  3. Other antiprotozoals – For trichomoniasis.

  4. Anthelmintics – For worms (mebendazole, albendazole).

  5. Scabicides & Pediculicides – For mites & lice (permethrin, lindane).


📌 Clinical Application from Case Study

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.


🔥 High-Yield NCLEX Alerts

  • 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.

AMEBICIDES OVERVIEW

  • 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)


📌 Prototype: Metronidazole (Flagyl)

Pharmacokinetics

  • 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%).


Mechanism of Action (MOA)

  • Diffuses into microorganism cell → causes cell death.

  • Exact biochemical pathway unknown.

  • Works against anaerobic protozoa & bacteria.


Uses

  • Intestinal amebiasis

  • Amebic liver abscess

  • Trichomoniasis

  • Bacterial vaginosis

  • Not FDA-approved for amebiasis prophylaxis.


Black Box Warning

  • For metronidazole & tinidazole:

    Produced carcinogenic tumors in rats — only use for approved indications.


Special Populations

  • 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 ↑.


Dosing

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


Adverse Effects

  • CNS: Headache, dizziness, ataxia

  • GI: N/V/D, metallic taste

  • GU: Dark urine

  • Hypersensitivity: Rash, bronchospasm


Contraindications

  • Hypersensitivity to metronidazole.


Interactions

  • 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.


Nursing Implications

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)


Patient Teaching

  • 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.


🧪 Other Amebicides

  • 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.


💡 NCLEX-Style “Success” Q’s from the Book

  1. Q: Patient with amebiasis takes metronidazole, then a cough syrup with alcohol. What effect?
    A: Flushing (disulfiram-like reaction).

  2. Q: What assessment shows therapy is working?
    A: Diminished diarrhea.


📍 Clinical Application 25.2

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.

💊 ANTIMALARIAL OVERVIEW

  • 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.


📌 Prototype: Chloroquine Phosphate

Pharmacokinetics

  • 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.


Mechanism of Action (MOA)

  • Inhibits DNA & RNA polymerase → disrupts parasite metabolism.

  • Inhibits prostaglandins.

  • Raises parasite’s internal pH → stops growth.


Uses

  • 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.


Pregnancy & Lactation

  • Crosses placenta, detected in newborns — but safe for prophylaxis in pregnancy.

  • Same dosing for pregnant & nonpregnant adults.


Adverse Effects

  • 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.


Contraindications

  • Allergy to 4-aminoquinoline compounds.

  • Existing retinal or visual field changes.

  • Caution: porphyria, psoriasis, retinal disease, G6PD deficiency, alcoholism, pregnancy, lactation.


Interactions

  • ↑ effect: Cimetidine.

  • ↓ effect: Magnesium trisilicate, vitamin C (↑ urinary excretion).

  • Alcohol: ↑ GI distress.


Nursing Implications

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.


Patient Teaching – HIGH YIELD

  • 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.


📍 Other Antimalarials

  • 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.


📌 Success Question from the Book

Q: Which teaching is most important for chloroquine?
A: Have frequent ophthalmologic examinations.


📍 Clinical Application 25.3 – Ms. Michelson Teaching

  • 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.

💊 ANTHELMINTICS OVERVIEW

  • Purpose: Kill or expel parasitic worms (helminths) from the body.

  • Two primary drug groups:

    1. Ivermectin → strongyloidiasis, resistant lice.

    2. Benzimidazolesmebendazole (prototype), albendazole, triclabendazole.

  • Goal:

    • Eradicate parasite completely OR

    • Reduce worm burden so symptoms resolve.


📌 Prototype: Mebendazole (Emverm)

Pharmacokinetics

  • 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.


Mechanism of Action (MOA)

  • Blocks glucose uptake in helminths.

  • Depletes glycogen stores worms need for survival/reproduction → worm death.


Uses

  • 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.


Dosing

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


Adverse Effects

  • 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.


Contraindications

  • Hypersensitivity to mebendazole.


Interactions

Increase mebendazole toxicity:

  • Metronidazole → ↑ risk of adverse effects.

Decrease mebendazole concentration:

  • Aminoquinolines (antimalarials)

  • Carbamazepine

  • Phenytoin (book “Success” answer)


Nursing Implications

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).


Patient Teaching

  • 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.


📍 Other Anthelmintics

  • 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.


📌 Success Question

Q: Patient with enterobiasis on mebendazole — which agent ↓ serum concentration?
A: Phenytoin

💊 SCABICIDES & PEDICULICIDES OVERVIEW

  • Purpose: Kill lice (Pediculosis capitis, pubis) and mites (Sarcoptes scabiei).

  • Prototype: Permethrinfirst-line treatment for both lice & scabies.

  • Form: Topical cream/lotion.


📌 Prototype: Permethrin

Pharmacokinetics

  • Absorption: Minimal (~2%) through skin.

  • Metabolism: Liver (ester hydrolysis) → inactive metabolites.

  • Excretion: Urine.


Mechanism of Action (MOA)

  • 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)


Uses

  • 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.


Adverse Effects

  • Pruritus

  • Rash/erythema (especially scalp)

  • Burning, stinging, tingling, numbness, or pain at application site

  • Edema


Contraindications

  • Allergy to chrysanthemums, pyrethroid, or pyrethrin

  • Age < 2 months


Dosing & Administration

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.


Nursing Implications

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.


Patient Teaching

  • 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.


📍 Other Drugs in the Class

  • 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.


📌 Success Question

Q: Action of permethrin?
A: Inhibits sodium influx through parasite nerve cell membranes → paralysis & death.