- Medicine Information and Evidence for Policy > Medicines Policy
- Medicine Access and Rational Use > Rational Use
(1998; 113 pages)
Competing drugs for schistosomiasis treatment
Currently only three drugs are used on a global scale for the treatment of schistosomiasis: praziquantel, metrifonate, and oxamniquine. All three have a history of successful usage at the individual clinical level and in population or community-based chemotherapy (WHO, 1985), and all three appear on the WHO Model List of Essential Drugs. However, praziquantel remains the drug of choice for all forms of schistosomiasis occurring in man, because of its high efficacy, its low toxicity, and its ease of single, oral administration (Gustafson et al., 1987; WHO, 1993).
Oxamniquine is only effective against intestinal schistosomiasis (S. mansoni), and has been used successfully in South America. The effective dose varies between 15 mg/kg and 60 mg/kg given over two to three days, but dosage recommendations should be based on local experience (WHO, 1993). Capsules and syrup need to be kept in well closed containers, protected from light (WHO, 1993). It is a valid alternative drug for the treatment of S. mansoni; in fact, strains resistant to praziquantel still respond to this drug (Cioli et al., 1993; Fallon et al., 1994). However, oxamniquine has more side-effects and is more expensive than praziquantel, at least in Africa and in Latin America (Gryseels et al., 1987; Stelma et al., forthcoming).
Metrifonate is only effective against urinary schistosomiasis (S. haematobium), but it has been significantly less expensive than praziquantel-until recent price reductions in praziquantel. Metrifonate has been available at US$ 0.05 per 100 mg tablet in the international market, but must be given in 3 doses of 10 mg/kg two weeks apart. For a 50 kg adult, the medication cost for metrifonate would be US$ 0.25 per dose, and US$ 0.75 for three doses. The same individual would require a single dose of praziquantel (at 40 mg/kg), costing US$ 2.00 (at late 1980 prices of US$ 0.60 per 600 mg tablet), but now costing only US$ 0.50 per treatment (at the lowest available price of US$ 0.15 per tablet, in 1995)-less than the cost of a metrifonate treatment. Other factors also contribute to the choice of praziquantel over metrifonate. The metrifonate treatment schedule has a low rate of compliance, which leads to a generally lower cure rate than praziquantel (Utroska et al., 1989). Metrifonate tablets need to be kept in tightly closed containers and stored at temperatures not exceeding 25 degrees centigrade, preferably in refrigerators (WHO, 1993). A study from the Congo showed that praziquantel was more cost-effective than metrifonate in reducing schistosomiasis prevalence to a level of less than 5% of the population (Korte et al., 1986).