A note on the effect of metronidazole on the Nichols strain of Treponema pallidum in vitro and in vivo.

In addition to its effect on Trichomonas vaginalis, metronidazole has also been found to be active against the organisms causing Vincent's gingivitis. This has raised the question of its possible action on Treponema pallidum, although Scott-Gray and Murrell (1961) found that a short course of 1-8 g. given over 48 hours did not affect a case of primary syphilis, and Yobs, Clark, and Schroeter (1966) found that large doses did not affect the course of syphilis in rabbits infected with the Nichols strain of Trepomena pallidum. Davies (1967), however, has reported that doses of 2 to 4 g. daily caused the disappearance of Treponema pallidum from the lesions of six patients with secondary syphilis with subsequent healing of the lesions; smaller doses were without effect. Davies, McFadzean, and Squires (1964) have reported that the minimum inhibitory concentration of metronidazole for the cultivable Reiter treponeme is 0 02 [±g./ml. These observations prompted the examination of the effect of serum containing metronidazole on the Nichols strain of Treponema pallidum in vitro.