Comparative effects of two commercially available blood collection tubes on plasma concentrations of drugs.

Two commercially available blood collection systems (Venoject and Vacutainer) were investigated for their effect on the plasma concentrations of a variety of drugs. Vacutainer tubes adversely affected the following drugs: propranolol, penbutolol and quinidine, whereas Venoject tubes had no effect on the plasma concentrations of these drugs. Neither collection system had any effect on the plasma concentrations of the following drugs: acebutolol, the main metabolite of acebutolol (DL-1-(2-acetyl-4-acetamidophenoxy)-2-hydroxy-3-isopropylaminopropane), diazepam, N-demethyldiazepam, digoxin, ethosuximide, salicylic acid, valproic acid, warfarin and carbamazepine.