What is ivermectin?
Ivermectin is a macrocyclic lactone medicine used to treat parasitic infections. In New Zealand, ivermectin is available in 3 mg tablets (Stromectol™). Ivermectin cream (Soolantra™) was approved by the FDA in December 2014 but is not yet readily available.
What is ivermectin used for?
Ivermectin is effective against infections with:
- Parasitic worms including: onchocerciasis (river blindness), strongyloides, cutaneous larva migrans and filiariasis such as onchocerciasis
- Ectoparasites, including scabies
Ivermectin has been used extensively as part of the World Health Organisation's Onchocerciasis Eradication Program. It has FDA approval for the treatment of strongyloides and onchocerciasis in the United States, other use is termed ‘off label’.
In treatment of scabies its use may be appropriate in selected cases where topical therapy is impractical or has failed and is particularly useful in cases of crusted scabies (also called ‘Norwegian’ scabies).
Ivermectin can also be used to control demodicosis. Ivermectin cream has been shown to reduce papulopustular rosacea, which is thought to be due to its effects on demodex mites and its anti-inflammatory action.
How does ivermectin work?
Ivermectin stimulates excessive release of neurotransmitters in the peripheral nervous system of parasites. It is thought to work by paralysing the parasite or inactivating the parasite gut. In humans the neurotransmitters acted on by ivermectin are in the brain. A protective barrier, called the blood-brain barrier, blocks ivermectin from reaching the human brain.
Is ivermectin safe?
Oral ivermectin appears to be a safe medication.
Ivermectin is primarily metabolised in the liver by CYP450-3A47 and has a plasma half life of 16 hours. It is almost exclusively excreted in faeces with minimal clearance by the kidneys. It therefore does not require dose adjustment for people with renal failure. There have been some reports of a mild anti-coagulation effect. However, this is usually not significant enough to alter coagulation parameters such as the prothrombin ratio.
How is oral ivermectin taken?
Ivermectin is taken as a single dose with a glass of water. The tablets can be crushed, for example to be given via a percutaneous endoscopic gastrostomy (PEG) tube. It is rapidly absorbed from the gut and metabolised in the liver.
|Onchocerciasis||Single dose of 150mcg/kg (may be repeated every 3 to 12 months)|
|Strongyloidiasis||Single dose of 200mcg/kg|
|Scabies||Dose of 200mcg/kg repeated in 7 to 14 days|
|Cutaneous larva migrans||Single dose of 200mcg/kg|
Side effects of ivermectin
Side effects of oral ivermectin are rare and usually minor. These include:
- Transient tachycardia (fast heart rate)
- In treatment of onchocerciasis; fever, rash, muscle or joint aches and tender glands and eye irritation/swelling or pain
- In treatment of strongyloidiasis; diarrhoea, skin rash
- More severe neurological side effects are theoretically possible in rare susceptible individuals
The safety of ivermectin in pregnant women has not been studied and such use is not recommended. Studies in animals have shown an increase in birth defects. Safety and effectiveness in children under 15kg has not been established. Ivermectin passes into breast milk and use during breast feeding is not recommended.
Ivermectin cream can irritate and cause a burning sensation on treated skin.
Drug interactions with ivermectin
No significant drug interactions with ivermectin are recognised.