Stability of therapeutic drug measurement in specimens collected in VACUTAINER plastic blood-collection tubes

Recently Becton-Dickinson marketed a plastic serum-separator tube that uses the same serum-separator gel as the glass tubes. We studied the stability of therapeutic drugs stored in plastic tubes by comparing it with the stability of drugs stored in glass serum-separator tubes and plain red-top glass tubes. We observed no absorption of caffeine, primidone, N-acetylprocainamide, procainamide, theophylline, tobramycin, ethosuximide, acetaminophen, amikacin, valproic acid, methotrexate, salicylate, and cyclosporine in either plastic or glass serum-separator tubes. On the other hand, concentrations of lidocaine, quinidine, phenobarbital, and phenytoin were reduced after storing in both plastic and glass serum-separator tubes, especially with prolonged storage and small sample volume. The reduction in concentrations were due to slow absorption of those drugs by serum-separator gel.