Tinidazole, a synthetic imidazole derivative, has been used in the oral treatment of several protozoal infections - trichomoniasis, giardiasis and amoebiasis. Among the protozoal organisms inhibited by tinidazole are Trichomonas vaginalis, Trichomonas foetus, and Entamoeba histolytica. In vitro, tinidazole has been shown to possess antiprotozoal activity at least comparable to, and in some cases greater than, metronidazole. Tinidazole also has activity against some Gram-negative anaerobic bacilli, including Bacteroides spp. Following oral administration of a 2g dose, like metronidazole serum levels peak in about 2 hours but persist for longer. Any clinical significance of the longer plasma half-life (tinidazole 12.5h; metronidazole 7.3h) has yet to be demonstrated. Tinidazole is approximately 20% bound to plasma proteins. Only unchanged drug has been found in the plasma and urine of tinidazole-treated subjects, although metabolites have been detected in animal studies. A single 2g dose of tinidazole has been shown to be effective therapy in vaginal trichomoniasis and in urogenital trichomoniasis in males. Single-dose therapy in general offers advantages in regard to convenience, and in the treatment of a sexually transmissible disease such as trichomoniasis, single-dose therapy facilitates compliance of patient and sexual partner. In comparative studies, tinidazole, in both single-dose and traditional multiple-dose regimens, has been shown to be equivalent and often superior to other antitrichomonal agents, including metronidazole. In intestinal amoebiasis, tinidazole has been evaluated after both once-a-day and multiple daily dose regimens, with the former giving slightly better results. When both metronidazole and tinidazole were administered in multiple daily dose regimens, the two agents yielded similar cure rates; in one study fewer tinidazole-treated patients required a second course. Tinidazole has also been successful in some cases of amoebic liver abscess, but an advantage over metronidazole has not been demonstrated. Results in the treatment of giardiasis, especially with the single-dose regimen, are promising, and in one study, tinidazole proved effective in infections resistant to metronidazole. Even in large doses, tinidazole has been well tolerated, although rarely vomiting may occur and the patient may need to be re-treated with a multiple dose regimen.