Theophylline protein binding.

The binding of theophylline to human serum albumin and human plasma has been studied by equilibrium dialysis at 22 degrees C, pH 7.4. The binding data were analyzed according to the Scatchard model. The values of binding parameters obtained for human serum albumin (N1 = 1.8, K1 = 2.6 x 10(3) l/mol; N2 = 6.0, K2 = 7 x 10(2) l/mol) were quite similar to those obtained for human plasma (N1 = 1.8, K1 = 2.7 x 10(3) l/mol; N2 = 5.0, K2 = 8.6 x 10(2) l/mol). It is suggested that theophylline interacts with the albumin fraction in human plasma proteins. The percentage of theophylline protein binding was determined in serum from patients with asthmatic diseases and from healthy volunteers. pH of serum samples was adjusted to 7.4 just before dialysis. The mean of theophylline binding in patients was slightly but significantly higher (37.5 +/- 0.4%) than those found for healthy volunteers (35.5 +/- 0.3%). The intersubject variability of theophylline binding was relatively small in both groups due to the standardization of experimental conditions.