Single dose treatments have the important advantages of simple administration, excellent compliance, short-lived side effects (if any) and short period of drug pressure. However, drugs used for single dose treatments must possess important characteristics, namely, long half-life, effective concentration in tissues over a long period, and low toxicity. In tropical medicine, such drugs are an important advance in the treatment of malaria (mefloquine and halofantrine), schistosomiasis (praziquantel and metrifonate), filariasis (ivermectin), and genitourinary tract and intestinal infections.
Intestinal infections are one of the most frequent problems in tropical medicine. While a large number of cases of diarrhoea are of viral (rotavirus) or bacterial (Salmonella, Escherichia coli) origin, necessitating only oral rehydration, some are of parasitological origin (Giardia, Entamoeba histolytica, Strongyloides, Trichuris, Schistosoma) and can be cured by a single dose treatment (tinidazole, secnidazole, ivermectin, albendazole, praziquantel). Secnidazole is the nitroimidazole with the longest half-life and is, therefore, used in single dose treatments for Giardia, acute intestinal amoebiasis and E. histolytica cyst carriers. Single dose treatments of most intestinal parasites will be a major advance in the management of tropical infectious diarrhoea. In the next decade, opportunistic intestinal infections (Cryptosporidium, Isospora, Enterocytozoon) in AIDS patients that are refractory to treatment could be the major problem.