Degradation and metabolism of indocyanine green: high-pressure liquid chromatographic analysis.

Degradation of indocyanine green solution by exposure to light was studied by high-pressure liquid chromatography. Indocyanine green in an aqueous medium exposed to light changed rapidly into an unknown product. The plasma clearance rate and the biliary excretion rate of the unknown product were much slower than those of indocyanine green. Spectrophotometric scan revealed that the unknown product had almost the same absorption spectrum as indocyanine green. Therefore, if degraded indocyanine green solution were to be used in a liver function test, the clearance of indocyanine green assayed by spectrophotometry would apparently be much lower than that of undegraded indocyanine green. According to fast atom bombardment mass spectrometry, the molecular weight of the unknown product was 723, whereas that of indocyanine green was 775. The analysis of rat bile after injection of indocyanine green by high-pressure liquid chromatography revealed that about 1% of the administered indocyanine green was metabolized in the rat liver.