WHO Model Prescribing Information: Drugs Used in Parasitic Diseases - Second Edition
(1995; 152 pages) [French] [Spanish] View the PDF document
Table of Contents
View the documentPreface
Open this folder and view contentsProtozoa
Close this folderHelminths
Open this folder and view contentsCestode (tapeworm) infection
Open this folder and view contentsIntestinal nematode infection
View the documentTissue nematode infections
Open this folder and view contentsLoiasis
Open this folder and view contentsLymphatic filariasis
Open this folder and view contentsOnchocerciasis
Close this folderSchistosomiasis
View the documentPraziquantel
View the documentMetrifonate
View the documentOxamniquine
Open this folder and view contentsIntestinal, liver and lung flukes
View the documentSelected WHO publications of related interest
View the documentBack cover
 

Metrifonate

Group: anthelminthic agent
Tablet 100 mg

General information

Metrifonate is an organophosphorus compound originally used as an insecticide. It has selective and variable schistosomicidal activity against S. haematobium that results from its partial metabolism to a highly active anti-cholinesterase, dichlorvos. Schistosomal cholinesterase is more susceptible to this metabolite than that of the human host, but transient reductions in both plasma and erythrocyte cholinesterase activity are demonstrable at therapeutic dosage. However, despite early concerns about its potential toxicity, metrifonate is well tolerated and has been used effectively and extensively in large-scale control programmes.

Clinical information

Uses

Treatment of urinary schistosomiasis.

Dosage and administration

Adults and children: a dose of 7.5-10 mg/kg on three occasions at intervals of 2 weeks will cure 40-80% of cases.

Even when viable worms remain, egg counts after one year are reduced to less than 20% of pre-treatment levels.

Contraindications and precautions

Mass chemotherapy should not be undertaken in communities recently exposed to insecticides or other agricultural chemicals with an anti-cholinesterase action.

Treated patients should not receive depolarizing neuromuscular blocking agents such as suxamethonium until at least 48 hours have elapsed from the time of metrifonate administration.

Use in pregnancy and lactation

Metrifonate has not been shown to be teratogenic or embryotoxic, but it is preferable to delay treatment until after delivery unless immediate intervention is essential.

In the absence of information on whether metrifonate is excreted in breast milk, it should preferably not be administered to nursing mothers.

Adverse effects

Abdominal pain, nausea, vomiting, diarrhoea, headache and vertigo are common.

Cholinergic symptoms very rarely occur with currently recommended dosages.

Overdosage

Atropine sulfate (for adults, 1 mg every 6 hours) may be used as a specific antidote to relieve symptoms of cholinergic activity. This does not impair the antiparasitic action.

Storage

Metrifonate tablets should be kept in tightly closed containers and stored at a temperature not exceeding 25 °C, preferably in a refrigerator. Discoloured tablets should be discarded.

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