What is the typical dosing regimen for ivermectin in treating parasitic infections?

Ivermectin Dosing for Parasitic Infections

The standard dosing regimen for ivermectin in parasitic infections is 200 μg/kg as a single oral dose, with specific dosing adjustments based on the type of infection being treated. 1

Standard Dosing by Parasite Type

Strongyloidiasis

• Dose: 200 μg/kg as a single oral dose 1
• Administration: Take on an empty stomach with water
• Follow-up: Stool examinations should be performed to verify eradication
• For treatment failure: Consider repeating dose

Onchocerciasis

• Dose: 150 μg/kg as a single oral dose 1
• Retreatment intervals:
  • Mass treatment campaigns: Every 12 months
  • Individual patients: May be retreated at intervals as short as 3 months

Scabies

• Dose: 200 μg/kg as a single oral dose, repeated in 2 weeks 2
• For crusted scabies: Combination therapy with topical scabicide plus oral ivermectin 200 μg/kg on days 1,2,8,9, and 15 2

Cutaneous Larva Migrans

• Dose: 200 μg/kg as a single oral dose 3
• Response typically occurs within 24-48 hours
• Complete resolution usually within 7-14 days

Ascariasis

• Dose: 200 μg/kg as a single oral dose 2

Loiasis

• Dose: 150-200 μg/kg, most often as a single dose 2
• Some guidelines recommend:
  • Daily dosing for up to 10 days in endemic settings 2
  • Repetitive administration at monthly, quarterly, or biannual intervals 2
• Important microfilarial threshold: Keep below 8,000 mf/ml to minimize adverse reactions 2

Practical Dosing Table

For 3mg tablets:

• 15-24 kg: 1 tablet
• 25-35 kg: 2 tablets
• 36-50 kg: 3 tablets
• 51-65 kg: 4 tablets
• 66-79 kg: 5 tablets
• ≥80 kg: Calculate at 200 μg/kg 1

Administration Considerations

Bioavailability

• Taking ivermectin with food (especially high-fat meals) increases bioavailability approximately 2.5-fold 1
• For cutaneous larva migrans, increased bioavailability is achieved when taken with food 3

Special Populations

• Children: Not recommended for children weighing less than 15 kg 2
• Renal impairment: No dosage adjustment required 3, 1
• Liver disease: Safety of multiple doses in severe liver disease is not established 2
• HIV patients: Same treatment regimen as HIV-negative individuals 2, 4

Treatment Efficacy and Follow-up

• Strongyloidiasis: Single dose of 200 μg/kg showed superior efficacy compared to albendazole and similar efficacy to thiabendazole 1, 5
• For persistent strongyloidiasis: Consider 200 μg/kg for 2 consecutive days (100% cure rate reported) 5
• Scabies: 91% cure rate in HIV patients after single dose 4
• Cutaneous larva migrans: Improvement typically within 24-48 hours 3

Common Pitfalls and Precautions

1. Contraindications:

   • Exclude co-existing onchocerciasis or loiasis before administering 3
   • Not recommended for children weighing <15 kg due to risk of crossing blood-brain barrier 2

2. Monitoring:

   • Persistent eosinophilia after treatment may indicate treatment failure (77% not-cure rate) 5
   • Re-evaluate if symptoms persist after 1 week 3

3. Drug interactions:

   • Primarily metabolized by CYP3A4 1
   • Does not significantly inhibit CYP3A4, CYP2D6, CYP2C9, CYP1A2, and CYP2E1 at clinically relevant concentrations 1

4. Head lice considerations:

   • Not FDA-approved as a pediculicide 2
   • Has shown promising results in topical 1% preparation 2

By following these evidence-based dosing guidelines, ivermectin can be effectively used to treat a wide range of parasitic infections with minimal adverse effects.