Stability of therapeutic drugs in serum collected in vacutainer serum separator tubes containing a new gel (SST II).

The stability of therapeutic drugs in sera collected in Becton-Dickinson Vacutainer serum separator SST tubes has been well studied. Although most therapeutic drugs are stable, certain drugs such as phenytoin, carbamazepine, and phenobarbital decrease in concentrations over a long storage time. To circumvent this problem, Becton-Dickinson devised a new gel formulation. The authors studied the stability of 14 commonly monitored drugs in sera when stored on the new gel of the SST II tubes and compared the concentrations of drugs in sera stored in plain tubes (no gel), those stored in the old SST tubes, and those stored in the SST II tubes containing a new serum separator gel. The concentrations of most drugs studied did not decline even after 24 hours of storage in SST II tubes. After storage for 7 days in SST II tubes, the concentration of carbamazepine declined by 10% and that of phenytoin decreased by 4%. This is a significant improvement over the existing tube, where concentrations of several drugs declined with prolonged storage. The authors conclude that new SST II tubes are effective in collecting blood for therapeutic drug monitoring.