Add time:08/02/2019         Source:sciencedirect.com

The binding to human serum albumin (HSA) of two drugs which are chemically related to theophylline, 1-methyl-3-pro-pylxanthine (MPX), a new bronchodilator, and 3-propylxanthine (enprofylline), was investigated in vitro using an ultrafiltration method. The binding process involves one class of binding sites, with n = 2 and Kd1 = 0.403 mM and n = 1 and Kd1 = 0.906 mM for MPX and enprofylline, respectively. The binding of both drugs to HSA was shown to be dependent on pH with approximately 20% of MPX and 60% of enprofylline unbound at pH 6.60 and 10% and 40%, respectively, unbound at pH 7.45. Albumin concentration also had a significant effect on the binding of both drugs. Elevation of free fatty acid concentrations in the HSA solution resulted in an increase in the free fraction of both drugs. A study using oleic acid as a representative inhibitor revealed that the inhibitory effect of free fatty acid on MPX binding is due to competition for binding sites. These results suggest that free fatty acid may play a role in the decreased binding of MPX. The findings indicate that factors such as these that affect the protein binding of both drugs could be of importance when using the drugs with asthmatic patients in various disease states. Correspondence: T. Hasegawa, Department of Hospital Pharmacy, Nagoya University School of Medicine, Tsurumai- cho, Showa-ku, Nagoya 466, Japan.

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