Haloperidol Plasma Level Monitoring in Neuropsychiatric Patients

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Abstract
The available data on haloperidol pharmacokinetics and haloperidol plasma level monitoring in neuropsychiatric patients are reviewed and compared with authors' personal observations. It appears that although haloperidol disposition can be described by linear kinetics in volunteers, this is not the case in patients in whom a 7--10-fold variability in plasma levels is observed for the same dosage together with the possibility of saturation kinetics and/or first pass effect. Anticholinergics may interfere with haloperidol absorption, and significant differences in disposition rate and binding have been observed in children and cirrhotic patients. A clear correlation appears to exist between plasma concentrations and side effects or adverse reactions with threshold levels for extrapyramidal syndromes of 6--9 ng/ml. Threshold levels for therapeutic effects vary with syndromes and age. In Gilles de la Tourette syndrome, active levels are of the order of 1--3 ng/ml, whereas in psychotic syndromes levels of 10--15 ng/ml are requested. In mania, a good therapeutic effect has been observed with plasma levels of 2.5--4.5 ng/ml. In general, children require lower plasma levels for the same therapeutic effects. In chronic unresponsive schizophrenic patients, poor drug bioavailability is not the major factor for the lack of response, and the possibility that these patients constitute a nosological subgroup is suggested. Therapeutic drug monitoring of haloperidol appears justified because (a) no direct relationship exists between daily doses and haloperidol steady-state plasma levels; (b) there is a possibility of saturation kinetics at higher doses; (c) commonly associated drugs or diseases may alter the kinetic profile of the drug; (d) drug disposition is faster in children than in adults; (e) optimal plasma concentration appears to differ in various pathological syndromes and age groups; and (f) side-effects and adverse reactions are clearly related to haloperidol plasma levels.

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