Beta-cyclodextrins enhance bioavailability of pilocarpine

Area of Science:

• Ophthalmology
• Pharmaceutics
• Drug Delivery

Background:

• Cyclodextrins are known to improve drug solubility and absorption for oral and parenteral routes.
• Their potential in enhancing ocular drug delivery remains largely unexplored.

Purpose of the Study:

• To evaluate the efficacy of hydroxypropyl-beta-cyclodextrins in improving ophthalmic drug bioavailability.
• To assess the impact of cyclodextrins on the miotic effect of pilocarpine in rabbits.

Main Methods:

• Topical administration of pilocarpine solutions with and without 5% cyclodextrin to New Zealand White rabbits.
• Measurement of pupil diameter changes to determine dose-response.
• Electrophysiology, scanning electron microscopy, and viscosity measurements to assess corneal effects and formulation properties.

Main Results:

• Pilocarpine with cyclodextrin showed a dose-related miotic effect, with a significantly left-shifted dose-response curve (ED50 reduced from 64 to 19 micrograms).
• A 1:1 molar ratio of pilocarpine to cyclodextrin maximized bioavailability.
• Cyclodextrin did not negatively affect corneal epithelium integrity, ion transport, or barrier function.
• Increased bioavailability was not attributable to changes in solution viscosity.

Conclusions:

• Hydroxypropyl-beta-cyclodextrins significantly enhance the ocular bioavailability of pilocarpine via topical administration.
• The enhancement mechanism does not involve corneal damage or increased vehicle viscosity.
• Cyclodextrins represent a promising excipient for improving ophthalmic drug delivery.