Photo-isomerization of fluvoxamine in aqueous solutions.

The hydrolysis and photolysis of fluvoxamine, a selective serotonin reuptake inhibitor, in aqueous buffer solutions (pH 5, 7, and 9), in synthetic humic water, and lake waters were investigated in the dark and in a growth chamber outfitted with fluorescent lamps simulating the UV output of sunlight at 25 degrees C. No significant hydrolytic degradation/isomerization was observed for 30 days in all aqueous solutions. However, fluvoxamine was moderately isomerized to its (Z)-isomer by simulated sunlight. The photo-isomerization occurred in two stages. The photo-isomerization occurred rapidly within the first 7 days and slowly thereafter with a rate constant of 0.12-0.19 day(-1) for the first stage and 0.04-0.05 day(-1) for the second stage. Photosensitized rate constants in synthetic humic water and in lake waters were approximately 6-7 times faster than that in pH 9 buffer with the rate constants of 1.15-1.34 day(-1) in the first stage. The (Z)-isomer of fluvoxamine was the only product detected in all aqueous solutions and was identified using LC-ESI-MS.