Identification of 2-hydroxymethyl-olanzapine as a novel degradation product of olanzapine

Olanzapine (OLZ) is amongst the most commonly prescribed antipsychotic drugs and is associated with substantial instability. The aim of this study was to investigate the instability of OLZ and to identify the degradants formed from its breakdown. Three experiments were conducted to monitor the degradation of OLZ and the formation of degradants in blood (1), water (2), and post-extraction at 4 °C (3). All three sample sets were analysed in duplicate and repeated in the absence (A) and presence (B) of 0.25% ascorbic acid. One degradant was identified in sample sets 2A and 3A with m/z 329 and confirmed as 2-hydroxymethyl-OLZ (2-OH-OLZ) using LC-MS techniques. The addition of 0.25% ascorbic acid slowed the degradation of OLZ down in all three experiments and inhibited the formation of 2-OH-OLZ in sample sets 2A and 3A. To investigate the influence of oxygen on the degradation of OLZ and the formation of 2-OH-OLZ in water, an additional experiment (4) was conducted. Sample sets were prepared containing different vortexing or sonication steps in order to alter the oxygen content in the samples. Statistical analysis confirmed that degradation increased significantly following vortexing for 1 min while sonication did not affect the rate of degradation of OLZ further suggesting the involvement of oxygen in the degradative processes. 2-OH-OLZ was only identified as a degradant of OLZ in aqueous solutions. It also degrades over time but its product is currently unknown and is under investigation.