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Drug Reference

ivermectin

antiparasitic anthelmintic· Brands: Stromectol, Mectizan, SoolantraPOTOP

Mechanism of action
Ivermectin binds selectively to glutamate-gated chloride ion channels in invertebrate nerve and muscle cells. This increases chloride ion permeability, leading to hyperpolarisation, flaccid paralysis and death of susceptible parasites. It does not affect mammals because they lack these glutamate-gated chloride channels.
Pharmacokinetics
Ivermectin is well absorbed after oral administration, with peak plasma concentrations at around 4 hours. It is extensively bound to plasma proteins and metabolised in the liver by CYP3A4. The elimination half-life is approximately 15 to 18 hours in humans, but varies. Excretion is predominantly via the faeces as unchanged drug and metabolites.
Indications & dosing

Onchocerciasis (river blindness)

Single dose; repeat every 6-12 months as needed.

  • adult · PO: 150 mcg/kg ONCE · Single dose; repeat every 6-12 months as needed.

Strongyloidiasis

Single dose; for complicated infections repeat daily for 2 days.

  • adult · PO: 200 mcg/kg ONCE · Single dose; for complicated infections repeat daily for 2 days.

Scabiesoff-label

Repeat after 14 days; license varies by region.

  • adult · PO: 200 mcg/kg ONCE · Repeat after 14 days; license varies by region.

Lymphatic filariasisoff-label

Used in combination with albendazole or diethylcarbamazine; off-label.

  • adult · PO: 200–400 mcg/kg ONCE · Used in combination with albendazole or diethylcarbamazine; off-label.
Contraindications & precautions
  • Known hypersensitivity to ivermectin or any component of the formulation · Discontinue immediately if signs of allergy occur.
  • Co-infection with Loa loa (for treatment of onchocerciasis) · Risk of serious encephalopathy. Screen and treat loiasis first.
  • Pregnancy · Use only if potential benefit justifies risk to the foetus. Consider alternative therapy.
  • Children weighing less than 15 kg · Not recommended; safety and efficacy not established in this group.
  • Avoid use in pregnancy unless the potential benefit clearly outweighs the risk to the foetus.
  • Screening for Loa loa infection is recommended before treating onchocerciasis, especially in endemic areas, to prevent severe encephalopathy.
  • Use with caution in patients with epilepsy or other neurological disorders, as ivermectin can cause central nervous system side effects.
  • Caution patients about dizziness or somnolence; advise against driving or operating machinery until the impact is known.
  • Use with caution in hepatic impairment; consider dose reduction or monitoring for toxicity.
  • For scabies, treat all close contacts simultaneously and wash bedding and clothing to prevent reinfection.
Adverse effects
  • Pruritus
  • Dizziness
  • Headache
  • Nausea or vomiting
  • Mazzotti reaction (fever, rash, hypotension, tachycardia)serious
  • Encephalopathyserious
  • Seizuresserious
Renal & hepatic adjustment
  • Hepatic impairment (severe): Use with caution; no specific dose adjustment advised in mild to moderate impairment. For severe impairment, consider dose reduction or interval extension if toxicity risk.
Monitoring, pregnancy & toxicity
  • Clinical response (e.g., skin lesions, pruritus, parasitic clearance) · Before and during treatment; follow-up as clinically indicated
  • Neurological adverse effects (e.g., dizziness, headache, ataxia, somnolence) · During treatment and after each dose
  • Stool examination for strongyloidiasis (if applicable) · 2-4 weeks after treatment
  • Pregnancy: Ivermectin is not recommended during pregnancy, especially in the first trimester, due to lack of safety data. Use only if clearly indicated and benefits outweigh risks.
  • Toxicity: Nausea, vomiting, diarrhoea, dizziness, headache, ataxia, somnolence, tremor, seizures, hypotension or hypertension. · Treatment is supportive: ensure airway, breathing and circulation; monitor vital signs; treat seizures with benzodiazepines; consider activated charcoal within 1 hour of ingestion.
  • Toxicity: Severe toxicity may lead to respiratory depression, coma, and cerebral edema. · Supportive care includes mechanical ventilation if needed, and management of cerebral edema with osmotic diuretics. There is no specific antidote.
Clinical notes
Ivermectin is used primarily for the treatment of onchocerciasis and strongyloidiasis. It is also used for scabies and other ectoparasitic infections. The dose depends on the indication and is usually based on body weight. It should be taken on an empty stomach with water. Adverse effects include rash, pruritus, fever, headache, dizziness, and gastrointestinal disturbances. It is not effective against adult filarial worms at standard doses. In some regions, ivermectin is used as a mass treatment for lymphatic filariasis. It is not indicated for viral infections, including COVID-19. Prescribing decisions should be based on local guidelines and product information.

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BNF; local formulary