Detergent penetration into young and adult rabbit eyes: comparative pharmacokinetics

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Abstract
The ocular penetration and pharmacokinetics of two anionic (sodium lauryl sulfate [12-carbon chain] and an ethoxylated alkyl sulfate [18-carbon chain]) and one cationic (benzalkonium chloride) surfactant are compared with those of other ophthalmic drugs. Where possible, these comparisons are made between albino and pigmented and young and adult rabbits. There are significant differences between young and adult rabbits, both in terms of the mass of detergent entering the various tissue and fluid compartments of the eye and in the pharmacokinetics of surfactants in the two age groups. The differences between the C-18 and C-12 chain anionic detergents is pronounced, with the C-18 compound being retained for longer times. Young animals amass greater quantities of detergents per unit tissue weight. The cationic detergent does not enter the ocular fluids or internal tissues, being confined to the conjunctiva and cornea. Both anionic and cationic detergents show a very slow turnover once within the ocular tissues, while most ophthalmic drugs are lost from ocular fluids and tissues within a-relatively short time (i.e., less than 8 hr). Both anionic and cationic detergents are avidly retained by the cornea, in particular the epithelium, which acts as a reservoir for further diffusion of material to other sites.