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 the daily dose and plasma trough concentrations. The correlation was stronger when considering the combined concentrations of HL and RHL in hair. Additionally, hair sectioning allowed for the reconstruction of dosage history in patients with recent dosage changes, based on the distribution of the drugs along the hair length, assuming a growth rate of 1-1.5 cm/month.