B-303 Stability of Antipsychotic Drugs in Patient Serum and Plasma Clinical Samples

Abstract

Abstract Background Therapeutic drug monitoring (TDM) of antipsychotic blood levels is strongly recommended (clozapine and olanzapine) and recommended (risperidone, aripiprazole, and quetiapine) by ASCP/AGNP Consensus Statement. For effective TDM, it is paramount to understand both the stability of the antipsychotic drugs in serum and plasma, as well as any differences in levels due to sample matrix to ensure robust concentration determinations. While clozapine levels are considered equivalent in serum and plasma, we included in our study four additional antipsychotics. Methods Whole blood samples from ten patients taking clozapine, risperidone, aripiprazole, olanzapine, or quetiapine were collected in one red top tube and in one purple top tube according to an IRB-approved protocol. Samples were then processed within 2 hours of collection to obtain matched serum and K2EDTA plasma samples from each of the patients. CE marked immunoassays for the measurement of clozapine (also FDA cleared), total risperidone/paliperidone, total aripiprazole, olanzapine, and quetiapine were used to quantitate drug concentrations. Stability of the samples was assessed at 4°C, ambient room temperature (ART), and frozen at -80°C, with respect to their Day 0 concentration by measurement of six replicates at each timepoint using the immunoassays. Results Comparison of Day 0 values between serum and plasma for the same patient showed ±9% bias between sample matrices for all drugs, except olanzapine which showed differences up to ±15%. Average bias between serum and plasma was ≤-5% (olanzapine: -9%). All drugs were stable (±15% deviation from Day 0; olanzapine up to ±23%) in serum and in plasma for 7 days at both 4°C and ART and for up to 8 months frozen. Conclusions This study demonstrated that (1) the antipsychotic drugs clozapine, risperidone, aripiprazole, olanzapine, and quetiapine have sufficient stability in both serum and plasma for effective TDM and (2) for TDM, serum or plasma may be used.