Metrifonate in schistosomiasis - therapy and prophylaxis

The introduction and development of the organophosphorous drug metrifonate, first as an insecticide and then for the treatment of urinary schistosomiasis, has followed an unusual course. In its most widely accepted treatment regimen it is safe, effective and apparently without significant side effects. These facts, together with its low cost and ease of dosing, lead to a field trial of its efficacy in the treatment and prevention of infection in children in an area of high S. haematobium and S. mansoni endemicity in Rhodesia (Zimbabwe). Three doses of 7.5 mg/kg b.wt. given at fortnightly intervals reduced significantly the infection rates and the egg counts in S. haematobium patients. Subsequent treatment at the same dose level but at intervals of four weeks maintained a low level of infection and of egg output. On the other hand infection rates and egg output rose in unprotected children. There was however no comparable effect on S. mansoni. Apart from the expected and previously reported drop in cholinesterase values there were no untoward side effects: the exact significance of the drop in cholinesterase values remains unclear. The implications of these results for the wide-scale use of metrifonate as a therapeutic and as a prophylactic for Schistosoma haematobium infection is discussed.