Ocular Drug Delivery Flashcards
List 8 common ocular diseases
Blepharitis
Conjunctivitis
Uveitis
Dry-eye syndrome
Cataract
Diabetic retinopathy
Age-related macular degeneration
Glaucoma
What are the 2 sections of the eye?
Posterior
Anterior
What is the number one ocular delivery route?
Eye drops
What are the problems with eye drops?
Less that 5% of drug is absorbed
Poor patient compliance
What is an intravitreal Injection?
Injection directly into the vitreous humour
What are intravitreal injections used to treat?
Posterior segment eye diseases
Why do intravitreal drug injections not reach the retina?
Because of the inner limiting membrane
Separates the retina from the vitreous humour
What is a periocular injection?
Injection to the outer surface of the eye
List the types of periocular injections?
Peribulbar
Retrobulbar
Subtenon
Subconjunctival
What happens following periocular injection?
Drug diffuses across the sclera
Why do periocular injections have low bioavailability?
Due to :
Diffusion through sclera
Systemic clearance
Loss of drug before reaching target tissue
What type of ocular injections can be used to get drug to the retina?
Periocular injections
List some molecules that can be delivered by periocular injection
Corticosteroids
Immunoglobulins
DNA
Antisense oligonucleotides
What are the 5 main routes of ocular drug delivery?
Topical
Parenteral
Oral administration
Intravitreal
Periocular
What are the challenges with topical ocular drug delivery?
Poor uptake
Tear dilution
Short-acting
What are the challenges with parenteral ocular drug delivery?
Blood-aqueous barrier
Blood-retinal barrier
What are the challenges with oral ocular drug delivery?
Limited access to target ocular tissue with oral route
High doses would be required (side effects)
What are the challenges with periocular and intravitreal ocular drug delivery?
Poor patient compliance
Have to be given by specialist
However these are used to over come issues with topical/systemic dosing
What tissues are barriers to ocular drug delivery? (6)
Cornea
Sclera
Tear film
Conjunctiva
Vitreous humour
Blood-retinal barrier
How does the cornea act as a barrier to drug delivery?
Provides mechanical and chemical barrier
Negatively charged
Drug properties affect permeation rate through the cornea
How does the sclera act as a barrier to drug delivery?
Has a thick matrix of mucoploysaccarides and collagen
Drugs have to diffuse through holes in the matrix
How does the tear film act as a barrier to drug delivery?
The tear film acts to remove material from the surface of the eye
This would interrupt drug delivery
How does the conjunctiva act as a barrier to drug delivery
Tight junctions in conjunctival epithelium
Main barrier for drug penetration across the conjunctiva
How does the vitreous humour act as a barrier to drug delivery?
Gel structure - water,collagen & hyaluronate
Viscous
Delays the diffusion of drugs across vitreous humour
How does the blood-retinal barrier act as a barrier to drug delivery?
BRB restricts entry of drugs from the choroid to the retina
Name 3 non-biodegradable implants
Ocusert
Prosert
Vitrasert
Name 3 biodegradable implants
Lacrisert
Ozurdex
Sclera plugs
What are the advantages of ocular drug delivery? (Implants)
- Deliver constant therapeutic levels at site of action
- Bypass the blood brain barrier
- Release rates are below toxic levels
- High drug concentrations without systemic side effects
What type of implants are used to treat anterior-segment diseases?
Subconjunctival, intrascleral & transcleral
What type of implants are used to treat posterior-segment diseases?
Intravitreal, suprachoroidal, intrascleral & transcleral
What is Ocusert?
Membrane-controlled reservoir system for the treatment of glaucoma
What is the active agent in Ocusert?
Pilocarpine
Describe the design of Ocusert (PPQ)
Membrane Permeation-Controlled Drug delivery
Drug reservoir encapsulated in a rate controlling polymeric membrane
Describe the operation of Ocusert (PPQ)
Water penetrates the system and dissolves the drug
This will form a saturated soloiution
Saturated solution maintains constant release
Movement of drug is driven by diffusion
Follows zero order kinetics
Describe the Pilo-20 ocular therapeutic system
Release rate of 20ug/hour
For 7 days
5mg of pilocarpine in reservoir
List the advantages of Ocusert
More efficient use of pilocarpine
Reduces the number of instillations required
Higher drug concentration obtain than with eye drops
List the disadvantages of non-biodegrade implants
Retinal detachment
Vitreous haemorrhage
Requires retina specialist for administration
Requires antimicrobial eye drops after insertion
What is Ozurdex?
Biodegradable vitreous implant
Used to treat macular Edema
What is the active ingredient in Ozurdex and how long is it released for?
Dexamethsone
6 months
