Application site dependent ocular absorption of timolol.

Area of Science:

• Ophthalmology
• Pharmacokinetics
• Drug Delivery Systems

Background:

• Topical ocular drug delivery faces challenges in achieving uniform drug distribution.
• Timolol is a widely used beta-blocker for glaucoma treatment.
• Controlled-release systems aim to improve ocular drug bioavailability.

Purpose of the Study:

• To investigate the ocular absorption and distribution of timolol from silicone devices in rabbits.
• To compare ocular absorption of timolol administered via eyedrops versus controlled-release devices.
• To evaluate the effect of device placement (inferior vs. superior conjunctival sac) on timolol distribution.

Main Methods:

• Topical ocular administration of 3H-timolol in rabbits using eyedrops and silicone cylindrical devices.
• Devices released timolol at a controlled rate (7.2 micrograms/h).
• Analysis of timolol concentrations in various ocular tissues (cornea, conjunctiva, sclera, iris-ciliary body, aqueous humor) based on application site.

Main Results:

• Timolol distribution was uniform with eyedrop administration.
• Device application resulted in site-dependent, unequal timolol distribution in ocular tissues.
• Superior conjunctival sac placement led to increased corneal and overall ocular absorption compared to inferior placement.
• Low aqueous humor concentrations suggested significant noncorneal absorption from the inferior sac.

Conclusions:

• The application site of controlled-release timolol devices significantly impacts ocular absorption and distribution.
• Superior conjunctival sac placement enhances timolol bioavailability.
• Controlled release does not guarantee uniform distribution within the preocular tear fluid.