How can the bioavailability of timolol be enhanced? A pharmacokinetic pilot study of novel hydrogels

Abstract

• Background: Carbomerbased hydrogels with timolol maleate (T-Gel) were chosen to study the vehicle effect on ocular bioavailability. Pharmacokinetic profiles of T-Gel 0.05% (0.05% timolol), T-Gel 0.025% (0.025% timolol) and commercial timolol ophthalmic solution (TOS 0.1%; 0.1% timolol) were determined and compared. • Methods: A single dose was administered to rabbits' eyes. Timolol was determined by HPLC in aqueous humour, blood samples and washings of the ocular surface (as a measure of residence time). Sampling times were 0.5 h, 1 h and 4 h after instillation. • Results: Concentration versus time curves (AUC) of timolol in aqueous humour demonstrate no significant differences between TOS 0.1% and T-Gel 0.025% (P=0.19), whereas the difference between T-Gel 0.05% and TOS 0.1% is significant (P=0.006); the AUC ratio of T-Gel 0.05%:TOS 0.1%:T-Gel 0.025% was 2.14:1:0.87. Timolol blood levels were highest with TOS 0.1% at every time point. Peak levels occurred after 0.5 h with all test products; the ratio of peak levels (C_max) for T-Gel 0.05%:TOS 0.1%:T-Gel 0.025% was 0.55:1:0.17. Timolol was detected in the washings up to 1 h after instillation of test products; the highest levels were observed after T-Gel 0.05%. • Conclusion: The new vehicle obviously improves the bioavailability of topically applied timolol.