Olanzapine; Postinjection Syndrome; Pharmacokinetics in View.

Olanzapine is a second-generation antipsychotic that is frequently administered intramuscularly as a slow-release depot and maintenance treatment for schizophrenia. Therapeutic values range from 20 to 80 mcg/L and levels >100 mcg/L are considered toxic. Postinjection delirium/sedation syndrome (PDSS) is a rare but serious adverse effect after the injection of olanzapine depot formulations. The authors present a case study in which a 64-year-old patient presented to the emergency room 30 minutes after an intramuscular injection of olanzapine with signs of possible postinjection syndrome. The patient presented with hypertension, tachycardia, delirium, and was suspected to have PDSS. On admission, his serum olanzapine levels had reached 390 mcg/L, and blood samples were collected on days 0, 1, 3, and 12. The timing of his presentation at the emergency room made it possible to track the pharmacokinetics of olanzapine in detail. On the basis of therapeutic drug monitoring, a prolonged olanzapine half-life of 7 days was calculated. Symptoms such as agitation and hypertension improved after approximately 39 hours, and the patient had made a full recovery after 72 hours. This case study can serve as a reference for healthcare providers that will aid in the recognition and treatment of PDSS and contribute to a better understanding of the clinical problems associated with PDSS. In addition, it emphasizes how therapeutic drug monitoring may be of added value with respect to determining when medication can be safely resumed.