Drug interference in the Bradford and 2,2'-bicinchoninic acid protein assays

The interference of a range of drugs and related substances has been investigated in the Bradford Coomassie brilliant blue (CBB) protein dye-binding assay and the 2,2'-bicinchoninic acid (BCA) protein assays. Chlorpromazine was the only substance to interfere in the CBB assay but the interference was slight. In contrast, the BCA reagent interacted strongly with chlorpromazine, the penicillins, vitamin C, and paracetamol and the mode of interference varied with the test substance. The chlorpromazine produced turbidity and an atypical color. The penicillins show a slow but normal color response while vitamin C and paracetamol gave an immediate and intense response.