Light-dark variations in ocular timolol concentrations following topical solution instillation in the pigmented rabbit.

The objective of this study was to determine whether ocular absorption of topically applied timolol in the pigmented rabbit varied with the time of drop instillation. Twenty-five microliters of a 0.65% timolol maleate solution were instilled in the pigmented rabbit eye at 0600, 0900, 1200, 1500, 1800, 2100, 2400, or 0300 hr. Timolol concentrations in the conjunctiva, sclera, corneal epithelium, corneal stroma, aqueous humor, and iris-ciliary body at 15 and 30 min post-dosing were monitored using reversed phase HPLC. Ocular timolol concentrations were higher when the drug was administered during the light period (0900-1800 hr) than when it was administered during the dark period (1800-0600 hr). There exist, therefore, light-dark variations in the ocular absorption of topically applied timolol.