Ocular Pharmacokinetics and Availability of Topically Applied Baicalein in Rabbits

Abstract

Purpose: To evaluate the ocular pharmacokinetics and availability of baicalein following topical application. Methods: Hydroxypropyl beta-cyclodextrin (HP-β -CD) was used to formulate an aqueous eye drop to improve aqueous solubility of baicalein. A single dose of either baicalein suspension (1%) (Bai-SP) or baicalein (1%)/HP-β -CD (10%) solution (Bai-CD) was topically applied to rabbits. Aqueous humor and cornea were collected after 5, 10, 20, 30, 45, 60, 90, and 120 min. Baicalein concentrations were determined by high-performance liquid chromatography (HPLC) after extraction. Results: After topically applying Bai-CD, the baicalein concentrations in aqueous humor were significantly increased at 20–120 min except at 90 min compared with those of Bai-SP (p < 0.05). The highest levels of baicalein in aqueous humor (C_max, 4.11 ± 0.75 μ g/ml) were obtained after 30 min application of Bai-CD, 3.6 times greater than that corresponding to the Bai-SP at 20 min. The Bai-CD produced an over 2.1-fold bioavailability (AUC₀₋₁₂₀, area under the concentration time curve between 0 and 120 min) increase in aqueous humor compared to the Bai-SP. Peak baicalein concentration in cornea (56.53 ± 17.02 μ g/g) was achieved within 5 min after topical application of Bai-CD and 4.5 times higher than that of Bai-SP at the same timepoint. The baicalein levels in corneas obtained after application of Bai-CD were all much higher than those obtained by Bai-SP (p < 0.01), whereas the drug levels became undetectable 30 min after topical application of Bai-SP. Conclusion: Bai-CD formulation is superior to Bai-SP for increasing ocular bioavailability.

Keywords:

• aqueous humor
• baicalein
• cornea
• hydroxypropyl beta-cyclodextrin
• ocular pharmacokinetics
• rabbit