Serum concentrations of fluvoxamine and clinical effects. A prospective open clinical trial

This pilot study examined prospectively blood serum concentrations of fluvoxamine, side effects and therapeutic response after a fixed dosage of 100 mg fluvoxamine/day for 14 days. Twenty male and female patients who met the DSM-IV criteria of a major depression received 50 mg fluvoxamine b.i.d. for two weeks. On days 7 and 14 side effects and therapeutic response were registered and serum concentrations of fluvoxamine were determined. A Receiver Operating Characteristic (ROC) curve was constructed to determine a possible relationship between serum concentrations and clinical effects. The serum concentrations of fluvoxamine were highly variable, even when dosages were corrected for body weight, ranging between 23 to 227 microg/l. No relationship between serum concentrations and side effects was detectable. On the other hand, ROC analysis, conducted on day 14, revealed a significant upper concentration threshold of 85 microg/l (p < 0.01) with no responder above this threshold. The results of this pilot study should be regarded as a hint at the possible therapeutic benefits of lower fluvoxamine serum concentrations by means of lower fluvoxamine dosages. Furthermore, this indicates for the first time that therapeutic drug monitoring might be useful for patients under antidepressant therapy with fluvoxamine.