Some of the views expressed in the following notes on newly approved products should be regarded as preliminary, as there may have been limited published data at the time of publication, and little experience in Australia of their safety or efficacy. However, the Editorial Executive Committee believes that comments made in good faith at an early stage may still be of value. Before new drugs are prescribed, the Committee believes it is important that more detailed information is obtained from the manufacturer's approved product information, a drug information centre or some other appropriate source.
Stromectol (Merck Sharp & Dohme)
6 mg tablets
Indication: strongyloidiasis and onchocerciasis
Onchocerciasis is one of the world's major causes of blindness. As the vector for the causative nematode is found near rivers, the condition is also known as river blindness. Ivermectin is the first-line treatment. The drug can also be used as an alternative to thiabendazole or albendazole in the treatment of infestation with the helminth Strongyloides stercoralis.
Invermectin is derived from moulds found in soil. It is thought to act by stimulating the release of gamma-aminobutyric acid (GABA) from the pre-synaptic nerve terminals of the parasites. The inhibition of neurotransmission by GABA gives ivermectin a broad spectrum of activity against helminths. It is not thought to interfere with human neurotransmission.
One advantage of ivermectin is that a single dose is effective. The drug is taken on an empty stomach in a dose determined by the patient's weight. As paediatric data are limited, ivermectin is not recommended for children under 5 years old with onchocerciasis or children under 12 years with strongyloidiasis. The drug also causes fetal damage in animals and is present in breast milk. Pharmacokinetic data are
limited, but it is known that ivermectin and its metabolites are excreted in the faeces over approximately two weeks. The plasma half-life of the metabolites (3 days) is approximately 6 times longer than that of the parent compound.
Repeat doses of ivermectin are not recommended for strongyloidiasis, although, if possible, the stools should be re-examined to ensure the treatment has worked. In areas endemic for onchocerciasis, the dose can be repeated after 6 or 12 months.
The adverse effects of ivermectin vary slightly depending on the condition being treated. This is because the death of the parasite in patients with onchocerciasis can cause allergic or inflammatory responses. These can present as arthralgia, lymphadenopathy, fever, pruritus and skin rashes. Other adverse effects include headache, myalgia, oedema, tachycardia, fatigue, dizziness and tremor.