Ocular pharmacokinetics and availability of topically applied baicalein in rabbits

To evaluate the ocular pharmacokinetics and availability of baicalein following topical application.

Hydroxypropyl beta-cyclodextrin (HP-beta -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-beta-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.

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 (Cmax, 4.11 +/- 0.75 microg/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 (AUC(0-120), 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 microg/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.

Bai-CD formulation is superior to Bai-SP for increasing ocular bioavailability.