Factors influencing the protein binding of a new phosphodiesterase V inhibitor, DA-8159, using an equilibrium dialysis technique

Various factors influencing the protein binding of DA-8159 to 4% human seru m albumin (HSA) were evaluated using an equilibrium dialysis technique at a n initial DA-8159 concentration of 5 mug/mL. It took approximately 8 h incu bation to reach an equilibrium between 4% HSA and an isotonic phosphate buf fer of pH 7.4 containing 3% of dextran ('the buffer') using a Spectra/Por 2 membrane (mol. wt. cut-off: 12000-14000) in a water bath shaker kept at 37 degreesC and at a rate of 50 oscillations per min. The extent of binding w as dependent on DA-8159 concentrations, HSA concentrations, incubation temp erature, buffer pH, and alpha-1-acid glycoprotein (AAG) concentrations. The binding of DA-8159 in heparinized human plasma (93.9%) was significantly h igher than in rats (81.4%), rabbits (80.4%), and dogs (82.2%), and this cou ld be due to differences in AAG concentrations in plasma. Copyright (C) 200 0 John Wiley & Sons, Ltd.