Absence of age effect on plasma haloperidol neuroleptic levels in psychiatric patients

Plasma neuroleptic levels in 41 patients (21 men, 20 women, aged 18 to 74) on haloperidol therapy were examined in relation to their age by means of radioreceptor assay. There was no significant difference among three age groups (below 45 years, 46 to 60 years, over 60 years) in the ratio of the plasma neuroleptic level to daily dose (nM/mg/kg), but a significant difference in the plasma neuroleptic level was found between the average values in parkinsonian (19.1 +/- 8.5 nM, M +/- SD) and nonparkinsonian (5.5 +/- 3.0 nM, M +/- SD) patients. There was, however, no significant difference in the incidence of parkinsonian symptoms between the young (below 60 years) and the old (over 60 years) age groups. These results suggest that in contrast to the previously reported study with chlorpromazine, the plasma neuroleptic level of haloperidol is not altered with aging and that parkinsonian symptoms induced by haloperidol occur simply in a plasma-neuroleptic-level-dependent manner.