Doses, serum concentrations and diagnoses of Norwegian quetiapine users 2001-2019 in a therapeutic drug monitoring material.

Over the past decade, increasing off-label use of quetiapine has been reported worldwide from various sources. We wanted to investigate how this is reflected in therapeutic drug monitoring (TDM) data. Requisitions for serum concentration measurements of quetiapine from a TDM service in Central Norway during 2001-2019 were obtained and analysed for age, gender, trends in quetiapine doses, serum concentrations and indicators of diagnoses.

Distribution of quetiapine between serum and whole blood in therapeutic drug-monitoring specimens.

Quetiapine use is on the rise, leading to a corresponding increase in acute intoxications, some of which have fatal outcomes. When assessing whole-blood quetiapine concentrations during forensic autopsies, interpretations are primarily based on toxicity data from studies of serum concentrations. To our knowledge, there are only two previous studies that have attempted to establish the ratio between whole blood and serum quetiapine concentrations with limited populations and high variability of results.