In 2000 the World Health Organization (WHO) stopped recommending metrifonate for treating urinary schistosomiasis because the drug did not appear to be as effective as the treatment of choice, praziquantel. Now a systematic review published in the latest edition of The Cochrane Library indicates that both metrifonate and praziquantel are effective at treating the infection. The team of researchers who carried out this study suggest that metrifonate may be a valid addition to the current one-drug strategy against urinary schistosomiasis.
These findings were reached after considering the data in 24 trials that together involved 6,315 participants.
Urinary schistosomiasis occurs when a tiny worm, a blood fluke (Schistosoma haematobium), penetrates a person's skin while walking or bathing in fresh water contaminated with snails that contain the worm. The fluke lays eggs in the body, and these eggs cause tissue damage that leads to blood in urine and pain on passing urine. If left untreated they can cause serious disease including kidney failure. Estimates indicate that more than 100 million people in African and Eastern Mediterranean regions are infected by the flukes, resulting in considerable social and economic hardships.
Praziquantel requires only one dose and is operationally more convenient, while metrifonate requires three at 14-day intervals. This could be a strong reason for stopping metrifonate use, especially in rural community-based treatment programmes, where it is difficult to give multiple doses. However, the researchers believe that it would be prudent to have more than one drug in use in order to minimise the chance of the organism developing resistance against the only drug, praziquantel.
"Relying only on praziquantel for treating schistosomiasis is a risky strategy as it could encourage the development of drug resistance," says lead researcher Anthony Danso-Appiah, who works at the Liverpool School of Tropical Medicine, Liverpool, UK.