We recommend a therapeutic range of 20 to 40 mcg/L based on the review by Bishara et al. (1). The half-life of the drug is 30 to 60 hours and measurement should occur at the earliest one week after starting therapy. Most patients will achieve therapeutic levels with doses of 10 to 15 mg per day. There are variations of drug levels with sex (women have higher levels for the same dose) age (younger and older patients might have higher concentrations) and smoking (smokers have lower levels).
Olanzapine is an atypical antipsychotic drug helpful in the treatment of schizophrenia, mania and related agitation. It is an effective antipsychotic drug with relatively low risk of upper middle symptoms and hyperprolactinaemia, but has been associated with weight gain and hypoglycaemia. Most patients achieve therapeutic plasma levels with doses of 10-15 mg/d. Olanzapine has a half-live of 30-60 hours and it takes about seven days to achieve steady-state. There is extensive metabolism of olanzapine by the cytochrome P-450 enzyme family (CYP1A2, CYP2D6, CYP3A4. Further metabolism is by the flavin containing monooxygenase and via glucuronidation. Metabolites are clinically not active. There is no universally agreed therapeutic range and the evidence that higher concentrations are associated with a better response is missing. Based on data showing optimal dopamine receptor occupation with plasma concentrations of 20- 40 mg/L (1) we adopt these recommendations rather than the higher suggested therapeutic ranges of the Arbeitsgemeinschaft fur Neuropsychopharmakologie und Pharmakopsychiatrie (AGNP) (2).
1. Bishara et al. Olanzapine: A Systematic Review and Meta-Regression of the Relationships Between Dose, Plasma Concentration, Receptor Occupancy, and Response. J Clin Psychopharmacol 2013;33: 329-335
2. Hiemke C, et al. Consensus Guidelines for Therapeutic Drug Monitoring in Neuropsychopharmacology: Update 2017 [published correction appears in Pharmacopsychiatry. 2018 Jan;51(1-02):e1]. Pharmacopsychiatry. 2018;51(1-02):9–62. doi:10.1055/s-0043-116492