Protein binding of disopyramide–-displacement by mono -N-dealkyldisopyramide and variation with source of α-1-acid glycoprotein

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Abstract
The binding of disopyramide to human serum proteins and human α-l-acid glycoprotein (AAG) was determined over a wide drug concentration range. Addition of 3.7 times 10−5 mol litre−1 mono- N-dealkyldisopyramide caused a 20–100% increase in disopyramide free fraction. The disopyramide free fraction in AAG solutions prepared from various commercially available sources of α-l-acid glycoprotein varied up to 2.5 fold at corresponding disopyramide concentrations. Pronounced differences in the calculated binding constants (affinity and capacity) were observed among the commercially available AAG preparations. These findings suggest that binding studies should be performed in appropriately harvested human serum or plasma to avoid possible artifacts associated with the use of commercial preparations of α-l-acid glycoprotein for binding studies.