Binding of aprindine and moxaprindine to human serum, ?1-acid glycoprotein and serum of healthy and diseased humans

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Abstract
Summary A comparison was made between the binding of the anti-arrhythmic agents aprindine and moxaprindine to human serum, to human serum albumin (HSA), to α1-acid glycoprotein (α1-AGP) and to a mixture of HSA and α1-AGP. In serum from healthy volunteers (n=4) the binding of aprindine-HCl 5 µg/ml (13.8 µM) was 93.8% (SD±1.0), and that of moxaprindine-HCl 5 µg/ml (12.8 µM) was 94.1% (SD±1.1). Their binding to the mixture of α1-AGP and albumin approximated their binding to serum. For α1-AGP, the binding was similar for both compounds, whereas for HSA the binding of aprindine was more pronounced than that of moxaprindine: for both products the affinity coefficient for binding to α1-AGP was about 100 times greater than that for binding to albumin. In serum from rheumatoid patients and from patients with renal failure a small but significant increase in binding of aprindine and moxaprindine was observed, approximately 1%. Increased and decreased binding was seen in serum from cirrhotic patients; for example, for aprindine the range in cirrhosis was 96.7%–79.8%, and the range in controls was 95.0%–92.4%. Free drug fraction and α1-AGP concentration were inversely correlated. The results show that α1-AGP plays an important role in the binding of aprindine and moxaprindine, and that alteration in the binding of the two compounds in disease states to a large extent can be explained by changes in serum α1-AGP concentration.