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Drugs for treating urinary schistosomiasis

22 Jul 2008

Paul Chinnock

Source: Cochrane Database of Systematic Reviews (see original article)

Citation: Danso-Appiah A, Utzinger J, Liu J, Olliaro P (2008). Drugs for treating urinary schistosomiasis. Cochrane Database of Systematic Reviews 2008, Issue 3. Art. No.: CD000053.

2008 The Cochrane Collaboration. Published by John Wiley & Sons, Ltd.

Schistosomiasis is caused by parasitic blood flukes called Schistosoma. The disease is endemic to 74 countries, affecting at least 200 million people, half of whom live in Africa. It is considered to be one of the most socioeconomically damaging parasitic diseases. Humans become infected when they come into contact with water into which fluke larvae have been shed by the snails that are the parasite’s other host. When the fluke’s eggs develop in people they cause pain and damage internal organs. Anaemia, malnutrition and an increased risk of cancer are other consequences. One species of Schistosoma (S. haematobium) infects the blood vessels of the bladder causing urinary schistosomiasis.

Several drugs have been used or tried for the treatment of urinary schistosomiasis and later abandoned because of poor effect or adverse events. Two, however, have been extensively used – praziquantel and metrifonate. In 2000 a Cochrane systematic review (1) looked for trials of the effectiveness of drug treatment. Five trials were found and, while none of them directly compared praziquantel and metrifonate, it was praziquantel that appeared to be more effective. Also in 2000 the World Health Organization stopped recommending metrifonate, on the basis that it was less effective and more costly to use than praziquantel. In addition praziquantel requires only one dose, while metrifonate requires three doses at 14-day intervals making it operationally less convenient. Praziquantel is currently the only drug for urinary schistosomiasis on the WHO Model List of Essential Medicines

Since then, other drugs have emerged as potential treatment options for urinary schistosomiasis, including artemisinin derivatives, albendazole, and amoscanate.

Danso-Appiah et al. have now updated the Cochrane review. The researchers looked for treatment trials with any drug or combination of drugs for urinary schistosomiasis. Twenty-four trials (6315 participants) met their inclusion criteria: 20 trials evaluated praziquantel, nine assessed metrifonate, three assessed the combination of praziquantel with albendazole, and one trial assessed praziquantel plus artesunate. The reviewers do note the relatively poor quality of some of the trials.

Looking at the data comparing praziquantel and metrifonate, the reviewers concluded there was little difference in parasitological failure. Both appear to be effective treatments with few adverse effects. While noting once again that praziquantel is operationally the easier drug to use, the researchers believe that it would be prudent to have more than one drug in use in order to minimize the chance of the parasite developing resistance against it. They urge that metrifonate should be added to the WHO essential drugs list.

The reviewers also concluded that evidence so far available on the artemisinins was inconclusive, and further research is warranted on combination therapies.

Reference

1. Squires N (2000). Interventions for treating schistosomiasis haematobium. Cochrane Database Syst Rev. 2000;(2):CD000053. Available from: http://dx.doi.org/10.1002/14651858.CD000053

Note: This article is published in the Cochrane Database of Systematic Reviews which is not freely available in all countries. It may not be possible to see the full article from your country without taking out a subscription. In some developing countries, readers who are based in institutions may be able to access it through the HINARI programme.