A simple, sensitive and accurate method for the determination of tiquizium ion, a quaternary ammonium ion, in the human serum and urine is described. The method is based on the extraction of biological fluids with chloroform under alkaline conditions and on reversed-phase high-performance liquid chromatography. Quantitation is possible down to 0.2 ng/ml of tiquizium ion using 2 ml of serum and down to 2 ng/ml using 2 ml of urine. Serum levels and urinary excretion data are obtained with this method for twelve healthy volunteers who had received a 5 mg, 10 mg and 20 mg of oral dose of tiquizium bromide.
