Evaluation Of Ocular Pharmacokinetics For Three Formulations Of Pilocarpine Using The Rabbit Eye Model With RP-HPLC

[Objective]Pilocarpine is one of the most important drug to manage the primary angle-closure glaucoma (PACG). One percent pilocarpine solution has been commonly used every 15 minetes. The major disadvantage of the conventional formulation is low bioavailability, Short precorneal residence time due to the tear turn over, rapid nasolacrimal drainage of the instilled drug from the tear fluid and absorption of the drug through the lipophilic corneal barrier. Liposomes are synthetic biologicmembranelike vesicles. They can promote the absorption andlocalization of the liposome-encapsulated drugs and act as a "depot" releasing their content slowly. In this study, the ocular pharmacokinetics of three formulations of pilocarpine in the aqueous humor of rabbit eyes were investigated with the method of RP-HPLC.[Methods]The RP-HPLC method was established on a column of ODS-C18 with the mobile phase consisting of 0.5% of triethylamine (TEA) of phosphate solutions (10 mmol l-1, pH2.5) and acetonitrile (98:2 v/v). The detection wavelength was 215 nm. Total 90 rabbits were enrolled to divided into 30 groups, each consisting of 3 animals(6 eyes). Every 10 groups received 50 μL of 1% generic pilocarpine, 1% liposome pilocarpine and 4% gel pilocarpine, respectively. The aqueous humor was withdrawn at 5,10, 30, 40, 60, 90, 120, 180, 240 and 360 min after instillation. Pilocarpine was extracted from aqueous humor with dichloromethane. The drug was analyzed by reversed phase high pressure liquid chromatography (RP-HPLC).[Results]The linear calibration curve was obtained in the concentration range of 0.1~20 μg · mL-1. The average recovery was 68.10% ± 1.9%. The pilocarpine Liposome and Gel have higher aqueous humor concentrationthan generic pilocarpine at any time points measured (P=0.000~0.04). The AUC of liposome and gel of were 2.8 times higher than that of generic. Measurable amounts of 1% liposome were still observed 360 min after administration, while 4% pilocarpine gel group was zero and 1% pilocarpine solution group could not be measured at 180 min posterior to dropping.[Conclusion]Our study demonstrated that pilocarpine liposome significantly increases ocular bioavailability. It suggests that pilocarpine liposome could prolong the drug activity, decrease frequence of administration and reduce toxicity.