Olanzapine

General Information

Olanzapine (Zyprexa, Lilly) is an atypical antipsychotic agent with structural similarities to clozapine. It has high affinity for dopamine D1, D2, D4, 5HT2A, 5HT2C, 5HT3, a1-adrenergic, histamine H1 and five subtypes of muscarinic receptors and has been shown to improve both the positive and negative symptoms of schizophrenia. Dose-related side effects associated with olanzapine may include somnolence, weight gain, dizziness, peripheral oedema, and postural hypotension. Oral olanzapine is well absorbed. Olanzapine is extensively metabolised and distributed throughout the body, although the principal metabolites are thought to lack pharmacological activity. No metabolites accumulate in plasma on chronic dosage. Dosage is normally 5-20 mg/d (BNF recommended limit), but some patients are given up to 60 mg/d.

Mean plasma olanzapine half-lives are longer in elderly patients (65 y or more) (51.8 hr) as compared to adults (33.8 hr) and in females (36.7 hr) as compared to males (32.3 hr).

Olanzapine assay can be useful to:

• Assess adherence
• Assess adequacy of dosage
• Investigate suspected acute poisoning