(1995; 152 pages) [French] [Spanish]
Group: anthelminthic agent
Tablet 100 mg
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.
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.
Abdominal pain, nausea, vomiting, diarrhoea, headache and vertigo are common.
Cholinergic symptoms very rarely occur with currently recommended dosages.
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.
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.