Effect on neuromuscular transmission of repeated administration of an organophosphorus compound, metrifonate, during treatment of children with urinary schistosomiasis.

Muscle action potential amplitude recorded from abductor pollicis brevis in response to nerve stimulation was measured in 55 children during treatment of urinary schistosomiasis with metrifonate (3 doses at 2 weekly intervals). Mean erythrocyte cholinesterase activity was 52-75% of pretreatment value in different groups when examined electrophysiologically. Twenty-six children acted as controls. There was no difference in amplitude between control and exposed subjects 2 weeks after the 2nd dose. Six hours after the 3rd dose, amplitude was larger in some subjects. This effect was not related to dose or degree of cholinesterase inhibition and was thought unlikely to be the result of treatment. Three children who received the highest dose of metrifonate had developed repetitive activity 6 hr later. The criteria for its identification are described.