What is the appropriate use of Ivermectin for parasitic infections?

Appropriate Use of Ivermectin for Parasitic Infections

Ivermectin is indicated primarily for strongyloidiasis of the intestinal tract and onchocerciasis, with excellent efficacy also demonstrated for cutaneous larva migrans and certain ectoparasitic infestations.

FDA-Approved Indications

• Strongyloidiasis: Single oral dose of 200 mcg/kg on an empty stomach with water 1

  • Efficacy: 64-100% cure rate following a single dose 1
  • Follow-up stool examinations needed to confirm parasite clearance 1

• Onchocerciasis (River Blindness): Single oral dose of 200 mcg/kg 2, 1

  • Requires repeated treatment (every 3-6 months until asymptomatic, then annually if necessary) 2
  • Important: Does NOT kill adult Onchocerca volvulus parasites, only microfilariae 1
  • Treatment protocol: Doxycycline 200 mg daily for 6 weeks (targets symbiotic Wolbachia) plus ivermectin 200 mcg/kg monthly for 3 months 2

Other Effective Uses (Off-Label)

1. Cutaneous Larva Migrans: Single dose of ivermectin 200 mcg/kg OR albendazole 400 mg daily for 3 days 2, 3

   • Clinical presentation: Characteristic itchy, serpiginous rash migrating 1-2 cm per day 2

2. Lymphatic Filariasis: Effective against microfilariae of Wuchereria bancrofti and Brugia spp. 4, 3

   • Not FDA-approved for this indication but used in mass treatment programs 4
   • For W. bancrofti/Brugia infection: Specialist input advised; diethylcarbamazine plus doxycycline typically recommended 2

3. Ectoparasites:

   • Highly effective for scabies (88% cure rate) and pediculosis (99% cure rate) 5
   • Particularly effective for crusted (Norwegian) scabies 4

Efficacy Against Other Parasites

• Ascaris lumbricoides: High efficacy (99% cure rate) 5
• Enterobius vermicularis: Excellent efficacy (100% cure rate) 5
• Trichuris trichiura: Moderate efficacy (84% cure rate) 5
• Hookworm infections: Limited efficacy (68% cure rate) 5

Important Clinical Considerations

Dosing and Administration

• Standard dose: 200 mcg/kg as a single dose on an empty stomach with water 1
• For strongyloidiasis in immunocompromised patients: May require repeated courses at 2-week intervals 1
• For onchocerciasis: Repeated treatment necessary as it only kills microfilariae 2, 1

Precautions

1. Loa loa co-infection: Screen for Loa loa before treating onchocerciasis in endemic areas

   • Risk of severe/fatal encephalopathy in patients with high Loa loa microfilarial loads 1

2. Pregnancy: Category C - not recommended during pregnancy 1

   • Teratogenic effects observed in animal studies at high doses 1

3. Breastfeeding: Excreted in human milk in low concentrations 1

   • Use only when benefits outweigh risks 1

4. Drug interactions: May increase INR when co-administered with warfarin 1

   • P-glycoprotein inhibitors may increase neurotoxicity 6

Adverse Effects

• Common: Edema, rash, headache, ocular complaints 6
• Severe reactions more likely in patients with hyperreactive onchodermatitis 1
• Mazzotti reaction: Inflammatory response to dying microfilariae in onchocerciasis treatment 1

COVID-19 and Ivermectin

The IDSA strongly recommends against ivermectin use for COVID-19 treatment in both hospitalized and ambulatory patients 2, 4:

• Multiple RCTs have shown no proven effect on mortality 2, 4
• The concentrations required to inhibit SARS-CoV-2 in vitro are much higher than achievable in human plasma 4

Key Takeaways

1. Ivermectin is highly effective for strongyloidiasis and onchocerciasis (FDA-approved indications)
2. It shows excellent efficacy for cutaneous larva migrans and ectoparasites
3. Variable efficacy against other intestinal helminths
4. Special precautions needed in Loa loa endemic areas
5. Not recommended for COVID-19 treatment

When prescribing ivermectin, always consider the specific parasitic infection, potential drug interactions, and follow appropriate dosing guidelines for the specific indication.