Development and validation of a HPLC-UV method for 4-(4-chlorophenyl)-4-hydroxypiperidine (CPHP), a toxic metabolite of haloperidol, in humans: Providing in vivo evidence of CYP3A4-mediated CPHP formation

We developed a high-performance liquid chromatographic procedure for the determination of 4-(4-chlorophenyl)-4-hydroxypiperidine (CPHP), a toxic metabolite of haloperidol, in human. Chromatographic analysis was performed on a reverse-phase C₁₈ column with a mobile phase containing 50 mM potassium phosphate buffer/acetonitrile (75: 25, vol/vol) using UV detection with a wavelength of 220 nm. The limits of detection for CPHP were 1 ng/ml in urine and the assay was linear over the concentration range of 2-500 ng/ml for urine. This analytical method was applied to measure CPHP in human. Nineteen healthy subjects were enrolled and all subjects received a single oral dose of 5 mg haloperidol following a treatment of placebo or itraconazole at 200 mg/day for 10 days in a randomized crossover manner. CPHP was detected in urine samples and average recovered amount of CPHP was 81.31 µg/24 hr in the placebo phase and it was significantly reduced to 30.34 µg/24 hr after itraconazole treatment. The finding provides in vivo evidence that CPHP is an in vivo metabolite of haloperidol in human and its formation is mediated by CYP3A4.