Determination of olanzapine and N-desmethyl-olanzapine in plasma using a reversed-phase HPLC coupled with coulochemical detection: correlation of olanzapine or N-desmethyl-olanzapine concentration with metabolic parameters

Abstract

Background: Olanzapine (OLZ) is one of the most prescribed atypical antipsychotic drugs but its use is associated with unfavorable metabolic abnormalities. N-desmethyl-olanzapine (DMO), one of the OLZ metabolites by CYP1A2, has been reported to have a normalizing action on metabolic abnormalities, but this remains unclear. Our aim was to explore the correlation between the concentrations of OLZ or DMO with various metabolic parameters in schizophrenic patients.

Methods: The chromatographic analysis was carried out with a solvent delivery system coupled to a Coulochem III coulometric detector to determine OLZ and DMO simultaneously in OLZ-treated patients. The correlation between the concentration of OLZ or DMO and the metabolic parameters was analyzed by the Spearman rank order correlation method (r s).

Principal findings: The established analytical method met proper standards for accuracy and reliability and the lower limitation of quantification for each injection of DMO or OLZ was 0.02 ng. The method was successfully used for the analysis of samples from nonsmoking patients (n = 48) treated with OLZ in the dosage range of 5-20 mg per day. There was no correlation between OLZ concentrations and tested metabolic parameters. DMO concentrations were negatively correlated with glucose (r s = -0.45) and DMO concentrations normalized by doses were also negatively correlated with insulin levels (r s = -0.39); however, there was a marginally positive correlation between DMO and homocysteine levels (r s = +0.38).

Conclusions: The observed negative correlations between levels of DMO and glucose or insulin suggest a metabolic normalization role for DMO regardless of its positive correlation with a known cardiovascular risk factor, homocysteine. Additional studies of the mechanisms underlying DMO's metabolic effects are warranted.

Figure 1. Representative chromatograms.

(A) pure standard of 5 ng/ml N-desmethyl-olanzapine, 5 ng/ml olanzapine and 80 ng/ml clozapine dissolved in mobile phase without extraction; (B) pure standard of 20 ng/ml N-desmethyl-olanzapine, 20 ng/ml olanzapine and 80 ng/ml clozapine dissolved in mobile phase without extraction; (C) blank extracted plasma sample; (D) Extracted plasma sample spiked with 5 ng/ml N-desmethyl-olanzapine, 5 ng/ml olanzapine and 80 ng/ml clozapine; (E) Extracted plasma sample spiked with 20 ng/ml N-desmethyl-olanzapine, 20 ng/ml olanzapine and 80 ng/ml clozapine.

Figure 2. Chromatogram of a SPE extracted serum sample from a patient who received 20 mg of OLZ daily. DMO, N-Desmethyl-olanzapine; OLZ, olanzapine; CLZ, clozapine.