Pizotifen increases 5-HIAA urinary excretion in male healthy volunteers.

A single dose of 0.5 mg pizotifen or a placebo was administered to 10 healthy male volunteers in a double blind cross-over trial. 5-hydroxyindoleacetic acid (5-HIAA) and homovanillic acid (HVA) in hourly urine samples were determined by liquid chromatography with amperometric detection. The 5-HIAA levels were strongly correlated with the HVA levels in control samples (r = 0.95, p less than 0.001). Pizotifen produced a significant increase in the urinary 5-HIAA/HVA ratio over the 3 hours following absorption of the drug (+0.21, +0.18, +0.19, p less than 0.05). The increase demonstrates an interaction between pizotifen and 5-HT metabolism, which may be involved in its antimigraine effect.