To evaluate loss due to adsorption of selected antipsychotic drugs in serum samples collected in blood collection tubes with and without separation gel using real clinical specimens.
Approach:
Sample Collection: Clinical serum specimens (n = 30 per drug) were obtained from paired blood collection tubes with and without separation gel.
Analysis Method: Samples were centrifuged and drug concentrations were measured by LC–MS/MS within 2 hours after centrifugation.
Storage Conditions: Serum aliquots were stored in a monitored refrigerator at 4°C and reanalyzed on Days 2 and 7.
Key Findings:
Clozapine concentrations were significantly lower in separation-gel tubes than in non-gel tubes on Day 0, with a mean relative reduction of 7.86%.
Clozapine remained stable in non-gel tubes with 99.1% on Day 2 and 98.3% on Day 7.
Clozapine in gel tubes decreased to 95.0% on Day 2 and 89.6% on Day 7, with significant loss on Day 7 (p < 0.001).
Aripiprazole showed a lower concentration in gel tubes on Day 0 but no further time-dependent loss in either tube type during storage.
No relevant loss was observed for the remaining antipsychotic drugs and metabolites.
Interpretation:
Most analytes showed no clinically relevant concentration loss during 7 days of refrigerated storage. Clozapine showed a measurable decrease in separation-gel tubes, suggesting an additional gel-associated contribution that may affect therapeutic drug monitoring interpretation.
Limitations:
Findings are specific to the evaluated tube brand, gel formulation, storage condition, and concentration ranges.
The study used a limited number of clinical specimens (n = 30 per drug).
Conclusion:
The study highlights the potential impact of separation gel on the stability of clozapine concentrations, which may influence therapeutic drug monitoring.
