Studies on the pharmacokinetics of fluorescein and its dilaurate ester under the conditions of the fluorescein dilaurate test.

Some aspects of the pharmacokinetics of fluorescein have been studied under the conditions of the fluorescein dilaurate test (Pancreolauryl-Test) in healthy volunteers. Dependence of fluorescein excretion on urine volume was investigated in a retrospective study in 370 patients. For intravenously administered fluorescein mean Cmax was 10.9 micrograms/ml with a mean elimination half-life of 286 min. For orally administered fluorescein sodium mean Cmax was 3.5 micrograms/ml with a tmax of 120 min and a t 1/2 of 267 min. Bioavailability of fluorescein by oral administration was 99%. By contrast, fluorescein from fluorescein dilaurate showed a 56% bioavailability under the conditions of the test with a Cmax of 1.8 micrograms/ml, a tmax of 270 min and a tt 1/2 of 246 min. Following enteral absorption of fluorescein hepatic extraction and enterohepatic circulation via the bile occurs, but although the concentrations of fluorescein in the bile may exceed those in the urine the absolute amount is likely to be small. In spite of the enterohepatic circulation fluorescein cleared from the urine within 24 h indicating that no delay between Part 1 and Part 2 of the test seems necessary. However, an adequate urine flow must be maintained throughout the test since a renal clearance/urine flow relationship exists, with fluorescein excretion being increased with increasing urine volume.