What is the dosing for ivermectin in adults and pediatrics?

Ivermectin Dosing Guidelines for Adults and Pediatric Patients

For adults and children weighing ≥15 kg, oral ivermectin should be dosed at 200 μg/kg (micrograms per kilogram) as a single dose, with a second dose typically recommended after 1-2 weeks for complete eradication of parasites. 1, 2

Adult Dosing

Strongyloidiasis

• Dosage: 200 μg/kg as a single oral dose 1
• Take tablets on an empty stomach with water
• Weight-based dosing guide:
  • 15-24 kg: 1 tablet (3 mg)
  • 25-35 kg: 2 tablets (6 mg)
  • 36-50 kg: 3 tablets (9 mg)
  • 51-65 kg: 4 tablets (12 mg)
  • 66-79 kg: 5 tablets (15 mg)
  • ≥80 kg: Calculate at 200 μg/kg 1
• Follow-up stool examinations should be performed to verify eradication

Scabies

• Dosage: 200 μg/kg as a single oral dose, repeated after 1-2 weeks 2
• Take with food to increase bioavailability 2
• For severe or crusted scabies, combination therapy with permethrin 5% cream may be considered 2

Pediatric Dosing

Children ≥15 kg

• Same dosing as adults: 200 μg/kg as a single oral dose 1, 2
• For scabies: Repeat dose after 1-2 weeks 2

Children <15 kg

• Traditional recommendation: Ivermectin has historically not been recommended for children weighing <15 kg due to concerns about potential neurotoxicity and blood-brain barrier penetration 3, 2
• Emerging evidence: Recent studies support the safety and efficacy of ivermectin in children <15 kg 4, 5:
  • For children 10-14 kg: A 3 mg fixed dose (approximately 250 μg/kg) has been shown to achieve comparable plasma exposure to older children receiving 200 μg/kg 5
  • For children 2-5 years: 300 μg/kg may be needed to achieve equivalent exposure to adults 6
  • For children 6-12 years: 250 μg/kg may be needed to achieve equivalent exposure to adults 6

Special Considerations

Strongyloidiasis

• Additional doses may not be necessary if follow-up stool examinations confirm eradication 1
• For immunocompromised patients or those with disseminated disease, a double dose of ivermectin (200 μg/kg) given two weeks apart may be more effective than a single dose 7

Scabies

• Ivermectin should be considered when topical treatments have failed or in cases of severe/crusted scabies 2
• Retreatment is necessary if living mites are demonstrable after 14 days, new lesions appear, or symptoms persist beyond 2-4 weeks 2
• All household members and close contacts should be treated simultaneously, even if asymptomatic 2

Safety Considerations

• Most common adverse effects are mild and include itching, rash, dizziness, and gastrointestinal symptoms
• Before treating with ivermectin, Loa loa infection must be excluded in people who have traveled to endemic regions to prevent severe adverse reactions 2
• Pregnant or lactating women should preferably be treated with permethrin 5% cream rather than oral ivermectin 3, 2

Monitoring and Follow-up

• For parasitic infections: Follow-up stool examinations should be performed to verify eradication 1
• For scabies: Evaluation should be performed after 1 week if symptoms persist 2
• Itching may persist for several weeks after successful treatment and is rarely a sign of treatment failure 2

Pitfalls and Caveats

1. Underdosing: Calculating the exact weight-based dose is critical; underdosing may lead to treatment failure
2. Retreatment timing: For scabies, the second dose should be given within 7-14 days to target newly hatched mites
3. Drug interactions: Be cautious with concomitant use of drugs that affect P-glycoprotein or CYP3A4
4. Weight estimation: Always weigh patients accurately rather than estimating weight, especially for children
5. Off-label use: Use in children <15 kg remains off-label in many countries despite emerging evidence of safety 4, 5

When treating parasitic infections with ivermectin, accurate weight-based dosing and appropriate timing of repeat doses are essential for achieving optimal clinical outcomes and preventing treatment failure.