Brain Pharmacokinetics and Tissue Distribution In Vivo of Fluvoxamine and Fluoxetine by Fluorine Magnetic Resonance Spectroscopy

Abstract

This investigation of fluvoxamine and fluoxetine-norfluoxetine distributions in vivo at steady-state and of quantitative kinetics in brain and plasma after drug therapy interruption was performed by fluorine nuclear magnetic resonance spectroscopy (19F MRS), spectroscopic imaging (MRSI), and plasma HPLC on 12 subjects treated for depression. MRSI suggests a homogeneous distribution of 19F MRS visible fluvoxamine mainly in brain. Fluvoxamine steady-state brain concentrations (12 ± 5 μM; n = 13) and brain-to-plasma concentration ratios (10 ± 2; n = 12) were similar to those of combined fluoxetine-norfluoxetine (CF-norfluoxetine) (13 ± 6 μM; n = 4 and 10 ± 6; n = 4). Fluvoxamine brain elimination half-life (79 ± 24 hours; n = 4) was significantly shorter than that of CF-norfluoxetine (382 ± 48 hours; n = 2). Fluvoxamine brain-to-plasma-half-life-ratio was 2.2 ± 0.3 (n = 4), contrarily to CF-norfluoxetine (1.0 ± 0.3; n = 2). This study shows that quantitative pharmacokinetics in target organs by 19F MRS in vivo should prove useful for understanding and investigating outcome of treatment modifications and side effects.