Pharmacokinetics of neuroleptic drugs and the utility of plasma level monitoring.

Variability in response to antipsychotic drug treatment may be caused by variable patient compliance, interactions with other drugs, pharmacokinetic variations and variations in concentration-response relationships at the receptor level. Pharmacokinetic variations may in some cases be compensated by individual dosage adjustments based on plasma drug level measurements. The interpatient variability in response to a certain time-course of drug concentrations at the receptor site could hitherto only be assessed by clinical judgement. New methods for in vivo assessment of receptor occupancy hold promise for possible measurement of parameters accounting for at least part of the interindividual variation in drug response at the receptor level. Monitoring of fluphenazine, perphenazine, thiothixene and sulpiride plasma levels by specific chemical assay methods seems to offer some guidance to individualization of drug doses. Definite therapeutic plasma level ranges have not been established for chlorpromazine and haloperidol. However, monitoring plasma levels of chlorpromazine or haloperidol might be of value when drug-induced toxicity is suspected, and as a means of controlling patient compliance.