Therapeutic Drug Monitoring (TDM) of Quetiapine in Clinical Practise

Therapeutic Drug Monitoring is a potent tool for optimizing pharmacotherapy in clinical practise. The Department of Clinical Pharmacology in the Hospital for Psychiatry, Psychosomatics and Psychotherapy of the University of Regensburg does not just return the determined drug concentration, but adds a clinical pharmacological comment to give back as much as possible of the information contained in the specimen. We tried to investigate the wide range of the serum levels of quetiapine, as observed in clinical practise and tried to verify insights gained in former studies under clinical conditions.

We acquired the serum levels of quetiapine of n=150 serum samples, collected under clinical every day-conditions. In consideration of gender, age, comedication and dosage we generated a database for statistical calculation.

Mean age was 41±15 years, 28% male, 48% female, in 9% gender was unknown. There was a highly significant positive correlation between dosage and serum levels (r=0,44; p=0,01). The differences of calculated clearances between quetiapine as single substance and prescribed together with carbamazepine was highly significant (p=0,01), whereas prescribed together with other drugs than carbamazepine there was no significant difference (p=0,97). The majority of calculated serum levels was outside the therapeutic reference range (72,7%). The mean total clearance (Clt/F) established was 146±102l/h.

TDM of quetiapine in clinical practise is explicitly recommended by the authors. Using TDM to determine dose related reference ranges in clinical practice supplements existing pharmacokinetic data.