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Variables Associated With High Olanzapine Dosing in a State Hospital
Background: Olanzapine has a U.S. Food and Drug Administration-approved dosing range of 10 to 20 mg/day but is often used at doses exceeding this range. Olanzapine is largely metabolized by cytochrome P450 (CYP) 1A2. Smoking, which induces CYP1A2, is expected to increase clearance of olanzapine by 40%; however, dosage adjustment in smokers is not currently recommended. Additionally, female gender is expected to reduce clearance by 30%. Many institutions target high-dose olanzapine prescribers in an effort to reduce unnecessary drug costs. However, factors such as smoking or gender may necessitate increased doses.
Method: A retrospective review of all patients receiving olanzapine during an inpatient stay at a state psychiatric hospital in Kentucky during 2001 was conducted. Demographic information and smoking status were collected for all patients. Olanzapine doses of > 20 mg/day were considered high doses.
Results: Nine percent (48/522) of olanzapine patients were prescribed high doses. The percentages were similar in women and men (10% vs. 9%, p = .69) and in smokers and nonsmokers (9% vs. 9%, p = .82). Moreover, the mean maximum olanzapine dose was also similar in men and women (15.4 +/- 7.2 vs. 14.9 +/- 7.3 mg/day, p = .51). The odds of receiving a high dose of olanzapine were increased 2.1 for patients with a schizophrenia spectrum diagnosis (DSM-IV schizophrenia or other psychotic disorder). The odds of receiving a high dose of olanzapine were increased with each incremental increase in length of stay (intermediate length of stay [8-60 days], OR = 5.6; long-term length of stay [> 60 days], OR = 12.0, relative to acute length of stay [< 8 days]).
Conclusions: Neither gender nor smoking status was associated with receiving a high dose of olanzapine. The association of increased length of stay with high dose suggests that treatment resistance may be an important factor in receiving high daily doses of olanzapine.