The Measurement of Haloperidol and Reduced Haloperidol in Hair as an Index of Dosage History

The study developed a method to measure haloperidol (HL) and its metabolite, reduced haloperidol (RHL), in human scalp hair to assess dosage history. Hair samples from 59 patients on fixed HL doses for over 4 months showed significant correlations between hair concentrations of HL and RHL and both daily dose and plasma trough concentrations. The correlation was stronger when combining both substances' hair concentrations. Additionally, hair sectioning allowed for deducing individual dosage histories based on drug distribution along the hair, assuming a growth rate of 1-1.5 cm/month.