Pediatric dosing considerations in ophthalmology--dosage adjustments based on aqueous humor volume ratio.

By simplifying a pharmacokinetic treatment, an equation can be derived which predicts that equal areas under aqueous humor concentration-time profiles can be obtained by administering a dose to infants which is some fraction of the normal adult dose. This fraction is obtained by dividing the aqueous humor volume of the child by that of the adult. This theory has been tested using rabbits as an experimental model. Using literature values for aqueous humor volumes, it was possible to calculate what fraction of a dose of pilocarpine administered to 20-day-old rabbits would result in the same ocular concentrations of drug as in 60-day-old rabbits. When the experiment was performed, agreement between predicted and experimental values was excellent. Although admittedly an oversimplified treatment, these results are the first step in a comprehensive pharmacokinetic model which should result in a more rational approach to ophthalmic drug delivery in infants and children.