Fluorescein glucuronide

The dominant path of distribution and elimination in the vitreous depends on a molecule s physicochemical properties and its substrate affinity. Lipophilic compounds, such as fluorescein (250) or dexamethasone (251), and compounds subject to active transport mechanisms, tend to be eliminated via the retina (Fig. 16). On the other hand, hydrophilic substances, such as fluorescein glucuronide, and compounds with poor retinal permeability, such as fluorescein dextran, tend to exit the vitreous anteriorly through the hyaloid membrane into the posterior chamber and subsequently into the anterior chamber, where they are subject to elimination pathways for aqueous humor (250). In general, shorter vitreal half-lives are associated with elimination through the retina, with its high surface area, whereas longer half-lives are indicative of elimination through the hyaloid membrane. 

Volume and location of an intravitreal injection can impact the patterns of ocular distribution and elimination. Friedrich et al. demonstrated a substantial effect of both on vitreal distribution and elimination of fluorescein and fluorescein glucuronide (252), with evaluation of four extreme positions and two injection volumes, 15 or 100 pL. The mean drug concentration remaining in the vitreous 24 hours postdose varied up to 3.8-fold with injection position, and increasing injection volume reduced this effect. 

Figure 9 The pancreolauryl test allows an indirect assessing of exocrine pancreatic function. Orally administered fluorescein dilaurate is hydrolyzed by carboxylester lipase (identical to cholesterol esterase) liberating lauric acid and free, water-soluble fluorescein. The latter is readily absorbed in the small intestine, partly conjugated in the liver, and excreted in urine mainly as fluorescein glucuronide. By measuring the concentration of fluorescein in the urine over a period of, for instance, 10 hours, the total quantity of this dye is determined. (From Ref. 52.)...

The anterior route has been found to be the primary elimination pathway for small, hydrophilic compounds such as gentamicin (74), fluorescein glucuronide... 

Larsen M. Ocular fluorometry methodological improvements and clinical studies—with special reference to the blood-retina barrier permeability to fluorescein and fluorescein glucuronide. Acta Ophthalmol Suppl 1993 211 1-52. 

Orally administered fluorescein is readily absorbed in the small intestine. By contrast fluorescein coupled to dilaurate cannot be absorbed unless the composite molecule is cleaved intra-duodenally by the pancreatic cholesterol esterase to form lauric acid and (absorbable) fluorescein. After its absorption, fluorescein is partly glucuronidated in the liver and then excreted in urine, predominantly as fluorescein diglucuronide. Thus, in pancreatic-insufficient... 

Koyano S, Araie M, Eguchi S. Movement of fluorescein and its glucuronide across retinal pigment epithelium-choroid. Invest Ophthalmol Vis Sci 1993 34 531-538. 

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