Nitroimidazoles in the canine prostate, vagina, and urethra

Diffusion of metronidazole and tinidazole in canine prostatic secretion was studied and compared to the diffusion of metronidazole into the canine vagina. This particular comparison was made because prostatic secretion represents an acidic environment in contrast to the canine vagina which has a basic pH. Metronidazole reached significantly higher concentrations in the prostatic secretion (PS) than in plasma (P). No differences were found in the concentrations of tinidazole in P and PS. Plasma and prostatic interstitial fluid (PIF) concentrations of both drugs showed no differences either. However, the PS/P and PIF/P ratios of metronidazole were significantly higher than the corresponding ratios of tinidazole. Metronidazole concentrations in the canine vagina and urethra were significantly lower than the plasma concentrations, possibly because of the basic pH environment. These findings suggest a possible advantage in using metronidazole over tinidazole in aerobic and Trichomonas vaginalis prostatitis and vaginitis in acidic environments. However, clinical studies comparing the two drugs should be carried out in order to establish if this is of clinical importance.