Plasma quetiapine in relation to prescribed dose and other factors: data from a therapeutic drug monitoring service, 2000–2011

摘要

Suggested predose plasma quetiapine target ranges for effective therapy in schizophrenia lie between 50 and 500 μg/l. We aimed to examine data from a quetiapine therapeutic drug monitoring (TDM) service to assess the plasma quetiapine concentrations attained at specified doses in clinical practice. We studied TDM data from patients given immediate-release quetiapine in the period 2000–2011. There were 946 samples from 487 patients (257 males, age at time of first sample, median [range] 34 [14–87] years, and 230 females, age at time of first sample, median [range] 38 [10–92] years). The plasma quetiapine concentration was t = 3.6, df = 446, p versus females (641 [600–1240] and 548 [600–943] mg/day, respectively), although there was no difference in median dose (600 mg/day) or in the mean (95% CI) plasma quetiapine concentrations attained. Smoking habit had no discernible effect on plasma quetiapine concentration. There was a poor relationship between dose and plasma quetiapine concentration in this study, as found by others. This is probably because of the short plasma half-life of the drug, at least in part. Nevertheless, quetiapine TDM can help assess adherence and measurement of quetiapine metabolites, notably N-desalkylquetiapine, as well as quetiapine itself may enhance the value of quetiapine TDM in future.