Factors Affecting the Penetration of Antibiotics into the Aqueous Humour

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Abstract
The blood-aqueous barrier has (a) a sieve-like property, allowing substances to enter the aqueous via the intercellular spaces in the iris; this is the route for water-soluble ions, and the limiting factor is molecular size; and (b) a lipoid property, by which lipoid-soluble substances enter the aqueous across the cell membranes; this can occur across all barriers bounding the aqueous. Penicillin exists in plasma principally in a strongly water-soluble ionic form and it therefore penetrates the blood aqueous barrier slowly. Chloramphenicol, which is more soluble in fat solvents, penetrates the barrier rapidly. Plasma proteins do not penetrate the normal blood-aqueous barrier, hence any antibiotic bound to plasma protein cannot pass into the aqueous.