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

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Abstract
Specimens of serum taken from 20 female patients with trichomoniasis under treatment with metronidazole in dosage of 200 mg 3 times a day for 7 days were mixed with suspensions of Nichols strain of T. pallidum and caused immobilization in many cases. Serum metronidazole levels ranged from 0 to 20.5 [mu]g/ml. The concentration of metronidazole producing 50% immobilization of treponemes averaged 5.2 [mu]g/ml. Metronidazole in the above dosage was ineffective in the experimental treatment of a patient with primary syphilis, although the patient''s serum on the 3rd, 5th and 7th days of metronidazole treatment reduced the percentage motility of treponemes in vitro. Patients receiving standard dosage of metronidazole for the treatment of trichomoniasis may develop concentrations of the drug which can affect T. pallidum; therefore sera from patients under treatment with metronidazole should not be submitted for TPI [T. pallidum immobilization] tests, as the presence of the drug may" Invalidate the result. A concomitant syphilitic infection would probably not be masked or aborted by treatment with the standard dosage of the drug.