Stability of Clozapine Stored in Oral Suspension Vehicles at Room Temperature: RESULTS
Accelerated Degradation and Assay Validation
At room temperature, a 0.5 mg/mL solution of clozapine in water to which 100 pL of 1% sodium hypochlorite had been added degraded rapidly, such that only 7.9% of the original concentration remained after 5 min. In samples to which smaller amounts of sodium hypochlorite were added, a greater percentage of the initial concentration remained after 5 min. In the degraded samples, several potential degradation products eluted before 4 min and at 6.4 min. None of the degradation products interfered with clozapine quantification (Figure 1). At room temperature, a 0.5 mg/mL solution of clozapine in water to which no sodium hypochlorite was added did not degrade, and no degradation products were observed after 24 h of storage. Given the degradation of clozapine in the presence of sodium hydrochloride and the chromato- graphic separation of the degradation products from clozapine, it was concluded that this analytical method was suitable for indicating stability.
Figure 1. Representative chromatograms of clozapine in methanol (panel A) and during the accelerated degradation study (panel B). For the degradation study, 25 pL of 1% sodium hypochlorite was added to 1 mL of a 0.5 mg/mL clozapine solution (panel B); the sample for analysis was obtained when 50% of the initial clozapine remained. Several potential degradation products eluted before 4 min and at 6.4 min; each of the largest peaks is marked with an arrow and an asterisk. A third chromatogram (panel C) shows degradation of clozapine when 75 pL of 1 % sodium hypochlorite was added to 1 mL of a 0.5 mg/mL clozapine solution. None of the degradation products interfered with clozapine quantification, and none were positively identified.
Analysis of standard curves and quality control samples during validation indicated that the clozapine concentration was measured accurately. Mean results for duplicate determinations of standards and quality control samples over the validation period indicated deviation of less than 3% from the expected concentration. Inter-day variation in the slope (as measured by CV) averaged 5.1%. Intra-day analytical reproducibility (as measured by CV) averaged less than 1% for each of the standards and quality control samples, indicating that differences of 10% or more could be confidently detected with acceptable error rates on duplicate analysis. During the study period, intra-day CV averaged 1.7% for samples and 1.4% for standards. Absolute deviation averaged less than 3.3% for all standards and quality control samples.