Mechanism of Action
Fluorescein sodium responds to electromagnetic radiation and light between the wavelengths of 465 to 490 nm and fluoresces, i.e., emits light at wavelengths of 520 to 530 nm. Thus, the hydrocarbon is excited by blue light and emits light that appears yellowish green. Following intravenous injection of fluorescein sodium in an aqueous solution, the unbound fraction of the fluorescein can be excited with a blue light flash from a fundus camera as it circulates through the ocular vasculature, and the yellowish green fluorescence of the dye is captured by the camera. In the fundus, the fluorescence of the dye demarcates the retinal and/or choroidal vasculature under observation, distinguishing it from adjacent areas/structures.
Within 7 to 14 seconds after IV administration into the antecubital vein, fluorescein usually appears in the central retinal artery of the eye. Within a few minutes of IV administration of fluorescein sodium, a yellowish discoloration of the skin occurs, which begins to fade 6 to 12 hours after dosing. Various estimates of volume of distribution indicate that fluorescein distributes into interstitial space (0.5 L/kg).
Fluorescein is metabolized to fluorescein monoglucuronide. After IV administration of fluorescein sodium (14 mg/kg) to 7 healthy subjects, approximately 80% of fluorescein in plasma was converted to glucuronide conjugate after a period of 1 hour post dose.
Fluorescein and its metabolite are mainly eliminated via renal excretion. After IV administration, the urine remains slightly fluorescent for 24 to 36 hours. A renal clearance of 1.75 mL/min/kg and a hepatic clearance (due to conjugation) of 1.50 mL/min/kg have been estimated. The systemic clearance of fluorescein was essentially complete by 48 to 72 hours after administration of 500 mg fluorescein.
Carcinogenesis, Mutagenesis, Impairment of Fertility
There have been no long-term studies done using fluorescein in animals to evaluate carcinogenic potential.