Lecture 5 - Ocular drug delivery

Question 1

List the barriers in ocular drug delivery.

Answer 1

Poor permeability of the cornea
Tear reflex
Blinking
Nasolacrimal drainage
Non-corneal absorption

Question 2

Why is the corneal barrier not easy to penetrate?

Answer 2

There are two tissue layers that affect permeability. The corneal epithelium which is a hydrophobic layer and the stroma is a hydrophilic layer.

Question 3

Why are prodrug used for ocular drug delivery?

Answer 3

The prodrug gives better absorption. For example latanoprost is used as a prodrug which is hydrolysed by esterases in the cornea.

Question 4

Give examples of substances that will improve precorneal retention.

Answer 4

Viscous systems (polyvinyl alcohol, hydroxyethylcellulose)
Mucoadhesives (Carbopols, carbomer)
Phase transition systems(in situ gelling systems)
Change in pH(cellulose acetate phlatate and carbomer)
Change in temperature (phuronic)

Question 5

List the problems with medicated contact lens.

Answer 5

Burst release profiles

Poor loading capacity for many drugs

Question 6

Give examples how to improve the medicated contact lens?

Answer 6

Multilayered contact lens ( zero order kinetic release profiles and can last a month)
Drug-loaded nanoparticles within the lens

Question 7

What is an ocular inserts?

Answer 7

It consist of a central reservoir of the drug enclosed between 2 semi permeable membrane. Ocusert is one example, used to deliver pilocarpine for glaucoma. Ocusert is used for 12h because the insert will swell and fragment.

Question 8

List the different ways of intraocular drug delivery

Answer 8

Intravitreal injection
Liposomes
Microparticles and nanoparticles
Intraocular devices
Iontophoresis