Fluorescein in human plasma in vivo.
In connection with corpus vitreum fluorophotometric examinations fluorescein was injected iv and fluorescein in the blood stream was studied with respect to protein binding and elimination kinetics. It was shown by ultrafiltration that in blood obtained during the examination most of the fluorescein was protein bound, and only a minor fraction (10-20%) was free in the water phase. While the free fraction was approximately constant over a wide concentration range when studied in vitro the free fraction increased by a factor of about 2 during a 2 h examination period in vivo. The curve describing the elimination of fluorescein from blood showed a polyexponential decline course. The area under this curve showed only a small variation for the same normal person examined 3 times over a period of 6 months. The area under the bolus has a magnitude, which is 30-40% of that under the rest of the curve.