Ivermectin !
Single-dose oral avermectin: the drug of choice for strongyloidiasis and onchocerciasis; it opens chloride channels found only in invertebrates.
Updated 2026-11-01
The figure shows ivermectin bound to the GluCl channel of Caenorhabditis elegans, a free-living nematode; it is the same channel family that parasitic worms have and humans lack.
Mechanism of action
It binds glutamate-gated chloride channels in invertebrate nerve and muscle and holds them open. Chloride flows in, the cell hyperpolarises and the worm is paralysed and dies. It also acts on GABA-gated chloride channels. In humans P-glycoprotein at the blood-brain barrier keeps it out of the brain, which explains its safety.
- Binds GluCl channels in worm nerve and muscle
- The channel stays open and chloride flows in
- The cell hyperpolarises: paralysis
- The worm or microfilaria dies
Pharmacokinetics
- Absorption
- Oral, on an empty stomach with water; a fatty meal greatly raises bioavailability
- Distribution
- Very lipid-soluble; P-glycoprotein keeps it out of the brain; little passes into milk
- Metabolism
- Liver, mainly by CYP3A4
- Elimination
- Almost all in faeces; under 1 % in urine
- Half-life
- About 18 hours
- Onset and duration
- Peak blood level about 4 hours after the dose
Indications
- Intestinal strongyloidiasis (drug of choice) and, with repeated dosing, hyperinfection Strongyloidiasis →
- Onchocerciasis (kills microfilariae, not adult worms)
- Scabies (used in some cases) Scabies →
- Head and pubic lice (used in some cases) Pediculosis (head, body and pubic lice) →
Adverse effects
Common
- Dizziness and itching
- Nausea, diarrhoea and abdominal pain
- Mild rise in transaminases and low white cells
- In onchocerciasis, the Mazzotti reaction: itching, fever, joint pain, swollen lymph nodes, oedema and tachycardia
- Orthostatic hypotension
Contraindications
- Hypersensitivity to ivermectin
- Pregnancy (safety not established)
- Confirmed or suspected Loa loa infection (relative)
- Impaired blood-brain barrier, such as meningitis
Key interactions
- Warfarin
- Rare reports of raised INR
- Levamisole
- Raises ivermectin levels
What is monitored
- Serial stool exams after Strongyloides treatment to confirm eradication
- Screening for Loa loa before treating anyone who has been in endemic areas of West or Central Africa
- Blood pressure and Mazzotti symptoms in onchocerciasis
- INR in patients on warfarin
- Level of consciousness
Administration and safety
- Oral, on an empty stomach with water; usually a single dose that is sometimes repeated.
- Human products only: the FDA warned against self-treatment with veterinary products.
- Immunocompromised patients may need repeated courses and cure may not be achievable.
- Safety has not been established in children under 15 kg.
Nursing care
- Before starting corticosteroids or immunosuppressants in people from endemic areas, think of Strongyloides: hyperinfection can be fatal.
- In onchocerciasis: get up slowly (orthostatic hypotension) and watch for fever, itching and joint pain in the first days.
- Report blurred vision, severe headache, confusion, drowsiness, seizures or trouble walking.
- Teaching: complete the follow-up stool tests; report pregnancy or breastfeeding.
Pregnancy and breastfeeding
The label says it should not be used in pregnancy because safety has not been established; WHO excludes pregnant women from mass campaigns. Small amounts pass into milk.
Test yourself
Think of the answer, then tap the question to see it.
What is ivermectin's target in worms?
Glutamate-gated chloride channels (GluCl) in nerve and muscle, which humans lack.
Why does ivermectin barely affect the human brain?
Because P-glycoprotein at the blood-brain barrier pumps it out.
What serious risk does ivermectin carry in a person with Loa loa?
Severe or fatal encephalopathy when Loa loa microfilaraemia is heavy.
What is the Mazzotti reaction?
An inflammatory reaction to dying microfilariae in onchocerciasis: itching, fever, joint pain, lymph nodes and oedema.
Why does ruling out Strongyloides before corticosteroids matter?
Because corticosteroids can trigger severe hyperinfection; ivermectin is the treatment.
Related drugs
Related conditions
← Back to the class: Anthelmintics
Educational content on how drugs work; not a prescribing guide and no substitute for a health professional's advice. No doses are given.
Sources: DailyMed - IVERMECTIN tablet (DailyMed (U.S. National Library of Medicine), 2026); Ivermectin: MedlinePlus Drug Information (MedlinePlus (U.S. National Library of Medicine), 2025); Clinical Care of Strongyloides (Centers for Disease Control and Prevention (CDC), 2024); Goodman & Gilman's The Pharmacological Basis of Therapeutics, 14th ed., ch. 68 (McGraw Hill, 2023).
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Representative model, for educational purposes only.