Ivermectin

Overview

Ivermectin is a broad-spectrum antiparasitic agent belonging to the avermectin class. It is widely used to treat various parasitic infections such as onchocerciasis (river blindness), strongyloidiasis, scabies, and head lice. It is also used topically for rosacea. Ivermectin is on the World Health Organization's List of Essential Medicines.

How Ivermectin works

Ivermectin binds selectively to glutamate-gated chloride ion channels in invertebrate nerve and muscle cells, increasing cell membrane permeability to chloride ions. This causes hyperpolarization, paralysis, and death of the parasite. It also enhances the release of gamma-aminobutyric acid (GABA) at presynaptic neurons. In mammals, ivermectin does not readily cross the blood-brain barrier, limiting central nervous system toxicity under normal conditions.

Uses

• Onchocerciasis (river blindness): to reduce microfilariae load, not adult worms
• Strongyloidiasis (intestinal threadworm): first-line oral treatment
• Scabies: oral ivermectin for crusted or refractory scabies, often combined with topical agents
• Pediculosis (head lice): as a topical lotion
• Rosacea: 1% ivermectin cream for inflammatory lesions
• Other parasitic infections (off-label, based on clinical guidelines): ascariasis, trichuriasis, cutaneous larva migrans, and lymphatic filariasis (as part of mass drug administration)

Side effects

• Common: headache, dizziness, muscle pain, nausea, diarrhea, fatigue
• In onchocerciasis: Mazzotti reaction (fever, itching, rash, lymph node tenderness) due to dying microfilariae
• Serious: severe allergic reactions (anaphylaxis, angioedema), low blood pressure, fast heart rate, liver enzyme elevations, neurotoxicity (confusion, seizures, ataxia) especially in patients with heavy Loa loa infection

Precautions

• Contraindicated in patients with known hypersensitivity to ivermectin.
• Use with caution if the blood-brain barrier is impaired (e.g., in meningitis, African trypanosomiasis) due to risk of neurotoxicity.
• Concomitant use with drugs that enhance GABA activity (e.g., barbiturates, benzodiazepines, valproic acid) may increase risk of CNS side effects.
• Pregnancy: Category C—use only if potential benefit justifies the potential risk to the fetus. Breastfeeding: excreted in human milk; use with caution.
• Safety and efficacy in children weighing less than 15 kg have not been established for oral formulations.
• In Loa loa endemic areas, individuals with high microfilarial loads are at risk of severe encephalopathy; pre-treatment assessment is recommended.
• Mass drug administration programs require strict adherence to dosing guidelines and medical supervision.