Major Increase of Quetiapine Steady-State Plasma Concentration Following Co-Administration of Clarithromycin: Confirmation of the Pharmacokinetic Interaction Potential of Quetiapine

The modern, atypical antipsychotic quetiapine is increasingly being used in the treatment of schizophrenia. Here, we report a case of a 32-year-old male patient with schizoaffective disorder who reached a markedly increased plasma concentration of quetiapine upon co-administration of clarithromycin. As a consequence he developed severely impaired consciousness and respiratory depression requiring intensive care surveillance. We provide evidence for a potent inhibition of quetiapine metabolism mediated by clarithromycin leading to a markedly reduced apparent oral clearance and a substantially prolonged terminal elimination half-life. Hence, titration of a quetiapine maintenance dose guided by therapeutic drug monitoring is recommended whenever clarithromycin is co-administered.