What is the recommended dosing of Ivermectin for an adult patient with a parasitic infection?

Ivermectin Dosing for Parasitic Infections in Adults

The standard dose of ivermectin for most parasitic infections in adults is 200 mcg/kg (0.2 mg/kg) as a single oral dose, taken with food to enhance bioavailability, with specific repeat dosing intervals depending on the parasite being treated. 1, 2

Standard Dosing by Indication

Strongyloidiasis

• 200 mcg/kg as a single oral dose taken on an empty stomach with water 3
• For immunocompetent patients: single dose is typically sufficient 4
• For immunocompromised patients: 200 mcg/kg on days 1,2,15, and 16 to prevent hyperinfection syndrome 4
• Follow-up stool examinations are mandatory to verify eradication 3

Onchocerciasis

• 150 mcg/kg as a single oral dose taken on an empty stomach with water 3
• Retreatment intervals can be as short as 3 months for individual patients, though 12-month intervals are standard in mass distribution programs 3
• Critical pitfall: Must exclude co-existing loiasis before treatment - maintain microfilarial threshold below 8000 mf/ml to reduce risk of severe adverse events; consider albendazole or apheresis for higher loads 1

Scabies

• 200 mcg/kg orally, with mandatory repeat dose in 14 days 1
• For a 56-kg patient, this equals 12 mg total (four 3-mg tablets) per dose 1
• Must take with food for scabies to increase bioavailability and enhance epidermal penetration 1
• For crusted (Norwegian) scabies in immunocompromised patients: 200 mcg/kg on days 1,2,8,9, and 15, plus daily topical permethrin - requires specialist consultation 1, 2

Other Parasitic Infections

• Cutaneous larva migrans: 200 mcg/kg as a single dose 1
• Pediculosis pubis (pubic lice): 250 mcg/kg, repeated in 2 weeks 1
• Head lice: 400 mcg/kg on day 1 and day 8, taken with food (not FDA-approved for this indication) 5
• Loeffler's syndrome (empirical treatment): 200 mcg/kg once daily for 3 days 1

Critical Administration Guidelines

Food Timing

• Take with food for scabies and most parasitic infections to increase bioavailability approximately 2.5-fold 1, 2
• Exception: Strongyloidiasis and onchocerciasis require empty stomach administration per FDA labeling 3

Mandatory Second Doses

• Scabies requires a 2-week repeat dose due to limited ovicidal activity - forgetting this is a common pitfall 1
• Head lice requires day 8 repeat to kill newly hatched nymphs from eggs present at initial treatment 5

Special Population Considerations

Pediatric Patients

• Absolute contraindication in children weighing <15 kg or <10 years old due to potential neurotoxicity from blood-brain barrier penetration 1, 5
• Use permethrin 5% cream instead for scabies in this age group 1

Pregnancy and Lactation

• CDC and American Academy of Pediatrics classify ivermectin as "human data suggest low risk" in pregnancy and probably compatible with breastfeeding 1

Renal Impairment

• No dose adjustments required 1

Hepatic Impairment

• Use with extreme caution in severe liver disease - safety of multiple or high doses not well established 1, 2

Common Pitfalls to Avoid

1. Forgetting contact treatment for scabies - all household and sexual contacts within the previous month must be treated simultaneously 1

2. Inadequate follow-up expectations - itching may persist up to 2 weeks after successful scabies treatment due to allergic dermatitis; treat symptomatically with topical corticosteroids and oral antihistamines 1

3. Using ivermectin in immunocompromised patients without specialist consultation - one study showed increased mortality in elderly, debilitated persons, though not confirmed in subsequent reports 1

4. Incorrect weight-based calculations - for a 70 kg adult, the standard 200 mcg/kg dose equals 14 mg, not higher doses sometimes mistakenly calculated 2

5. Treating loiasis without checking microfilarial load - severe adverse events can occur if microfilarial counts exceed 8000 mf/ml 1

Efficacy Data

Research supports the guideline-recommended dosing, with cure rates of 88% for strongyloidiasis, 100% for ascariasis, and 85% for trichuriasis and enterobiasis at 30 days post-treatment 6. For onchocerciasis, doses of 150-200 mcg/kg achieve 97-99% microfilarial reduction at 3 months 7.