Interaction between fluvoxamine and cotinine or caffeine.

We examined the relationships between plasma fluvoxamine concentrations and plasma levels of cotinine and caffeine, respectively, under steady-state conditions in 30 patients who met DSM-IV criteria for a major depressive disorder and who were being treated with fluvoxamine. The daily dosages of fluvoxamine ranged from 50 to 200 mg (mean +/- SD 108 +/- 42 mg). Eleven patients were smokers and the remaining 19 were nonsmokers. The plasma fluvoxamine concentrations were significantly higher in nonsmokers (0.92 +/- 0.40 ng/ml/mg) than in smokers (0.56 +/- 0.28 ng/ml/mg); in addition, a trend towards negative correlations was observed between the plasma fluvoxamine concentrations and the plasma cotinine levels, although it was not significant. Significant positive correlations were found between the plasma fluvoxamine concentrations and the plasma caffeine levels. These findings are compatible with those in earlier reports that cytochrome P450 1A2 plays a major role in fluvoxamine metabolism.