Some aspects of the pharmacokinetics of fluorescein in normal and in diabetic subjects.

: A method for measuring the free fraction of fluorescein in plasma by ultrafiltration is tested. The coefficient of variation is 3%. Changes in pH and temperature from in vivo conditions at 37 degrees C to in vitro conditions are slight (less than 6%) and tend to minimize each other. To study the pharmacokinetics of fluorescein, 25 control subjects and 38 insulin-treated diabetics were examined after an intravenous injection of sodium fluorescein, 17 mg/kg body weight. 5, 45 and 120 min later, free fluorescein was significantly lower in the diabetics (5 min: 2.4 +/- 0.5 vs. 2.1 +/- 1.0, 45 min: 0.62 +/- 0.13 vs. 0.52 +/- 0.14, 120 min: 0.27 +/- 0.07 vs. 0.17 +/- 0.07 X 10(-5) g/ml, p less than 0.01 (mean +/- SD)). The renal excretion of fluorescein is reflected in a positive relation between serum creatinine and total plasma fluorescein at 45 and 120 minutes in the group of diabetics (Spearmans rho = 0.52, p = 0.04 and 0.53, p = 0.08, respectively).