Serum protein binding of sulfisoxazole and diazepam in patients with chronic obstructive pulmonary disease.

Binding of two acidic drugs, sulfisoxazole and diazepam, to serum proteins has been investigated in patients with chronic obstructive pulmonary disease and in a control group of healthy volunteers. Marked increases in the free fraction of both drugs in serum were detected in patients (14.5 +/- 0.8% versus 6.1 +/- 0.3% in the case of sulfisoxazole, and 5.8 +/- 0.5% versus 3.2 +/- 0.0% in the case of diazepam). Decreased serum albumin concentration appeared to play a role in the defective binding of sulfisoxazole, although when this factor was corrected, some correlation between serum binding of sulfisoxazole and PaO2 values was detected. Other factors have to be considered to explain the decreased binding of diazepam in the serum of patients with chronic obstructive pulmonary disease.