Summary.Aripiprazole is a novel atypical antipsychotic drug used in the treatment of schizophrenia. The sensitive and reproducible ion pair RPLC method was developed and validated for determination of aripiprazole and its nine impurities, which are significantly different in polarity. The separation was performed on Phenomenex Luna ® C18 column (5.0 μm particle size, 250 × 4.6 mm id) using a gradient mobile phase A (phosphate buffer pH 3.0) and mobile phase B (acetonitrile) at the working temperature of 25°C. The buffer was 1.11 g KH 2 PO 4 with 1.2 g sodium pentanesulfonate/L of the solution, adjusted to pH 3.0 with orthophosphoric acid. The flow rate was 1.0 mL/min. The detection was carried out at 215 nm using a diode array detector. The developed method was validated according to the International Conference on Harmonization (ICH) guidelines for specificity, limit of detection, limit of quantification, linearity, precision and robustness. The proposed method is convenient and reliable for the purity control in both raw materials and dosage forms.

The development of an RP-HPLC method for the separation of aripiprazole and its nine impurities was performed with the use of partial least squares regression, response surface plot methodology, and chromatographic response function. The HPLC retention times and computed molecular parameters of the aripiprazole and its nine impurities were further used for the quantitative structure-retention relationship (QSRR) study. The QSRR model, R(2):0.899, Q(2):0.832, root mean square error of estimation: 4.761, root mean square error of prediction: 6.614, was developed. Very good agreement between the predicted and observed retention times (t(R)) for three additional aripiprazole impurities (TC1-TC3) indicated the high prediction potential of the QSRR model for tR evaluation of other aripiprazole impurities and metabolites. The developed HPLC method is the first reported method for the efficient separation of aripiprazole and its nine impurities, which could be used for the analysis of an additional three aripiprazole impurities (TC1-TC3).

Stress stability testing represents an important part of the drug development process. It is used as an important tool for the identification of degradation products and degradation pathways, as well as for the assessment of changes in physical form of drug molecules. The impact of excipients on the stability of olanzapine confirms that levels of impurities and degradants are limiting parameters and are therefore used for stability evaluation. The major degradation product of olanzapine was identified as 2-methyl-5,10-dihydro-4H-thieno[2,3-b][1,5]benzodiazepine-4-one (III). The structure of III was determined by using LC-MS, IR and NMR. Compatibility and stress stability results demonstrated that tablet formulations of olanzapine are sensitive to temperature and moisture. In samples protected from moisture, the increase in concentration of III was shown to be highly temperature dependent and the degradation followed zero-order kinetics. In addition, studies of olanzapine with excipients and in formulated tablets revealed polymorphic phase changes in some samples, influenced by a combination of stress temperature and humidity conditions. Polymorphic transitions were monitored using x-ray powder diffraction (XRPD) analysis and exhibited no correlation between the phase change (appearance of a new polymorph) and the degradation process.