Proper Dosage and Usage of Ivermectin for Parasitic Infections
The proper dosage of ivermectin for parasitic infections is 200 μg/kg (micrograms per kilogram) as a single oral dose for strongyloidiasis and 150 μg/kg as a single oral dose for onchocerciasis, with specific weight-based tablet recommendations as outlined in FDA labeling. 1
Dosage Guidelines by Specific Parasitic Infection
Strongyloidiasis
- Dosage: 200 μg/kg as a single oral dose 1
- Administration: Take tablets on an empty stomach with water
- Weight-based dosing:
- 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 based on 200 μg/kg
Onchocerciasis
- Dosage: 150 μg/kg as a single oral dose 1
- Administration: Take tablets on an empty stomach with water
- Retreatment: In mass distribution campaigns, commonly at 12-month intervals; for individual patients, retreatment may be considered at intervals as short as 3 months
Pediculosis Pubis (Pubic Lice)
- Dosage: 250 μg/kg, repeated in 2 weeks 2
- Administration: Take with food to increase bioavailability
- Note: Ivermectin has limited ovicidal activity, necessitating repeat treatment after 14 days to kill newly hatched lice 2
Scabies and Other Ectoparasites
- Dosage: 200 μg/kg orally, repeated in 2 weeks 2, 3
- Administration: Take with food to increase bioavailability
- Alternative: For severe or crusted scabies, combination therapy with oral ivermectin and topical permethrin 5% cream may be considered 3
Special Considerations
Safety Profile
- Ivermectin is generally well-tolerated with over 25 years of clinical use 4
- The drug has a high margin of safety due to its high affinity for invertebrate neuronal ion channels and inability to cross the blood-brain barrier in humans 4
Contraindications and Precautions
- Weight restriction: Not recommended for children weighing less than 15 kg due to potential risk of crossing the blood-brain barrier 2
- Pregnancy: Use permethrin 5% cream instead of ivermectin for pregnant or lactating women 3
- Loa loa infection: Must exclude Loa loa infection in people who have traveled to endemic regions BEFORE treating with ivermectin to prevent severe adverse reactions 2
Drug Interactions
- P-glycoprotein inhibitors may increase neurotoxicity of ivermectin 5
- Caution in patients with genetic polymorphisms affecting P-glycoprotein 5
Monitoring and Follow-up
Efficacy Assessment
- For strongyloidiasis: Follow-up stool examinations should be performed to verify eradication of infection 1
- For ectoparasites: Evaluation should be performed after 1 week if symptoms persist 2
- Re-treatment might be necessary if:
- Parasites are still detected
- Eggs are observed at the hair-skin junction
- No clinical response is achieved with the initial regimen 2
Common Pitfalls to Avoid
- Failure to repeat treatment: Due to ivermectin's limited ovicidal activity, a second dose is often necessary after 2 weeks to kill newly hatched parasites 2
- Inadequate decontamination: Bedding and clothing should be machine-washed and dried using the heat cycle or removed from body contact for at least 72 hours 2, 3
- Neglecting concurrent infections: Patients with parasitic infections often have multiple concurrent parasites that may require additional or different treatments 6
- Mistaking post-treatment reactions for treatment failure: Itching or mild burning of the scalp may persist for many days after parasites are killed and is not a reason for re-treatment 2
Adverse Reactions
- Common mild effects include headache, dizziness, muscle pain, nausea, or diarrhea
- More serious adverse reactions are rare but may include:
- Mazzotti reaction in onchocerciasis patients (fever, rash, lymph node swelling)
- Encephalopathy in patients with high Loa loa microfilarial loads 2
Ivermectin remains a critical antiparasitic medication with established efficacy against a wide range of parasitic infections when used at appropriate dosages for specific indications.