Ivermectin

Ivermectin is a macrocyclic lactone medicine used to treat parasitic infections. It is effective against infections with:

• Parasitic worms including: onchocerciasis (river blindness), strongyloides, cutaneous larva migrans and filiariasis such as onchocerciasis
• Ectoparasites, including scabies

In New Zealand, Ivermectin is available in 3mg tablets (Stromectol™). The medicine is available on prescription but is not funded by PHARMAC.

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).

How does it 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.

Safety

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 it 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.

Side effects

Side effects are rare and usually minor. These include:

• Transient tachycardia (fast heart rate)
• Flushing
• Nausea
• Lightheadedness
• 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.

Drug interactions

No significant drug interactions are recognised.