Do evacuated blood collection tubes interfere with therapeutic drug monitoring?

The influence of various brands of evacuated blood collection systems (the old type, red stoppered Vacutainer; the new type, blue stoppered Vacutainer; Monoject and Venoject) on therapeutic drug monitoring was investigated. No interferences were found in the assay of ethosuximide, phenobarbital, phenytoin, valproic acid, digitoxin, digoxin, procainamide, gentamicin and theophylline. Using Monoject and old type Vacutainer tubes, lower levels were found in the disopyramide assay: 91.3 +/- 4.6% (p less than 0.05) and 91.7 +/- 7.0% (not significant) respectively, and in the quinidine assay: 82.8 +/- 6.7% (p less than 0.02) and 83.9 +/- 4.4% (p less than 0.001) respectively as compared with glass tubes. In the carbamazepine assay a decrease was found in the Monoject tubes only: 93.7 +/- 1.7% (p less than 0.01). The stoppers of Monoject tubes and the old type Vacutainer tubes contained the plasticizer tris-(2-butoxyethyl)phosphate (TBEP), which has been shown to be a potent inhibitor of the binding of several drugs to alpha 1-acid glycoprotein. Using the new type Vacutainer and the Venoject, no interferences were found.