Olanzapine, 2-methyl-4-(4-methyl-1-piperazinyl)-10H-thieno-
[2,3-b][1,5]benzodiazepine (I)

I

is an atypical antipsychotic drug with a high affinity for serotonin (5HT_2A/2C), dopamine (D_1-4), muscarinic (M_1-5), histamine H₁, and adrenergic α₁ receptors [1- 2]. Olanzapine is indicated for the treatment of patients with schizophrenia and psychosis of a schizoaffective nature.
We have developed a sensitive and selective HPLC method with electrochemical detection to determine the concentration of olanzapine in human plasma. The analysis was carried out on a reversed-phase column (Symmetry C18, 150 x 4.6 mm I.D., 5 μm) using a mixture of 0.06 M ammonium acetate (pH 5.90), acetonitrile and methanol (40:41:37, v/v/v) as the mobile phase. The flow rate was 0.69 mL/min. The detection voltage was + 0.6 V and the cell and column temperature were 36°C. The drug and internal standard (clozapine) were isolated from plasma using liquid-liquid extraction with ethyl acetate. The mean recovery of olanzapine and internal standard were about 90% and 82%, respectively. Ascorbic acid was added to the samples to inhibit degradation of olanzapine during extraction and storage. The lower limit of quantitation for the assay was established at 0.313 ng/mL. Repeatability, intermediate precision and accuracy were satisfactory.
The method for the assay of olanzapine in human plasma is sufficiently sensitive to apply during the pharmacokinetic and bioequivalence studies of this drug.

[1] J. T. Callaghan, R. F. Bergstrom, L. R. Ptak, C. M. Beasley, Clin.Pharmacokinet., 37 (1999) 177.
[2] O. V. Olesen, K. Linnet, Ther.Drug Monit., 21 (1999) 87

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