Probenecid inhibition of the outward transport of fluorescein across the human blood-retina barrier

Acta Ophthalmol (Copenh). 1994 Dec;72(6):663-7. doi: 10.1111/j.1755-3768.1994.tb04676.x.


The effect of probenecid on the outward transport of fluorescein from vitreous to blood was studied in 13 insulin-dependent diabetic patients with background retinopathy in a randomised double-masked placebo controlled cross-over study. Fluorescein and fluorescein glucuronide was separated in the vitreous and in plasma by differential spectrofluorometry. The data for fluorescein were analysed using a simplified mathematical model of the eye. The inward permeability was estimated from data obtained 1 h after injection and the outward transport from data obtained 7 h after injection. During placebo treatment the mean inward permeability was 3.75 x 10(-7) cm/sec and the mean outward permeability was 2.25 x 10(-5) cm/sec. During probenecid treatment the mean inward permeability was 3.34 x 10(-7) cm/sec and the mean outward permeability was 1.44 x 10(-5) cm/sec. Thus, we found no significant change in inward permeability (p = 0.5879), whereas a significant decrease of 36% was found in the outward permeability of fluorescein (p = 0.0171). The demonstration that the outward permeability, which is more than 100-fold higher than the inward permeability in the healthy eye, is significantly decreased by probenecid, demonstrates that active transport is involved in movement of fluorescein across the blood-retina barrier from the vitreous to the plasma.

Publication types

  • Clinical Trial
  • Randomized Controlled Trial
  • Research Support, Non-U.S. Gov't

MeSH terms

  • Adult
  • Biological Transport, Active / drug effects
  • Blood / metabolism
  • Blood-Retinal Barrier / drug effects*
  • Capillary Permeability / drug effects
  • Cross-Over Studies
  • Diabetes Mellitus, Type 1 / complications
  • Diabetes Mellitus, Type 1 / metabolism
  • Diabetic Retinopathy / complications
  • Diabetic Retinopathy / metabolism
  • Double-Blind Method
  • Fluorescein
  • Fluoresceins / metabolism*
  • Humans
  • Male
  • Middle Aged
  • Probenecid / pharmacology*
  • Vitreous Body / metabolism


  • Fluoresceins
  • Probenecid
  • Fluorescein