Drugs And The Eye

Question 1

Name two examples of lubricants which optometrists prescribe.

Answer 1

Hypromellose and sodium hyaluronate

Question 2

Name two anti-invectives which optometrists prescribe.

Answer 2

Fusidic acid and Chloramphenicol

Question 3

Name two systemic drugs used for allergies.

Answer 3

Antihistamines such as Cetirizine and Loratadine.

Question 4

What is the main type of drug administrated?

Answer 4

Topical

Question 5

What are peri-operative drugs?

Answer 5

Drugs that are used straight after surgery

Question 6

What are some pre-corneal factors of topical drugs ?

Answer 6

Tear turnover rate has great influence as sometimes nasolacrimal drainage can exceed corneal penetration which could lead to a higher risk of systemic toxicity which could also be increased due to larger drop sizes.
Larger drop size doesn’t necessarily mean more drainage due spillage.

Question 7

What is the link between bioavailability and drop size from an eye drop?

Answer 7

Multiple drops or a larger drop size does not mean there is more bioavailability which shown my the plateau in the graph.

Question 8

For glaucoma, beta blockers are administrated. What effect this does this have?

Answer 8

Beta receptors are blocked which reduces aqueous production in the eye.

Question 9

Why should a drug have a combination of both hydrophilic and hydrophobic properties?

Answer 9

Hydrophilic so its able to pass through the stroma.
Hydrophobic so it is able to pass through the epithelium.
This influences the rate of drug penetration.

Question 10

In its ionised form is a drug hydrophilic or hydrophobic?

Answer 10

Hydrophilic

Question 11

When a molecule loses a protein does it become ionised or non-ionised?

Answer 11

Ionised

Question 12

Can an ionised molecule penetrate the epithelium easily?

Answer 12

Yes

Question 13

Describe the process of a molecule penetrating through the ocular surface.

Answer 13

Firstly it loses a protein to become ionised so it can penetrate the epithelium. It then gains a proton to become non-ionised to penetrate the stroma. It then lose a proton to be ionised to penetrate through to decements membrane. Finally it gains a proton to be back to its non-ionised form- can be pH driven

Question 14

After corneal penetration, what happens to the drug and what can affect absorption after?

Answer 14

It goes to the target cells and then is eliminated through the anterior chamber by aqueous turnover and it is also absorbed through the tissues of anterior uvea. Melanin affects absorption (bioavailability) which is why a higher concentration may be required for darker irises.

Question 15

Name some interocular targets.

Answer 15

-Muscranic receptors in the ciliary body
-Carbonic anhydrase inhibitors (Dorzolomide-used for angle open glaucoma)

Question 16

Give an example of a pro drug and how metabolism effects the drug.

Answer 16

An example is a pro drug such as an anti-glaucoma drug. When it has come out the dropper it is inactive and not that effective. As it metabolises by the enzyme esterase it then becomes active.

Question 17

How is an introcular drugs excreted?

Answer 17

-Eliminated by aqueous humour
-Absorbed by uvea tissue

Question 18

Name three factors which effect the systemic drug delivery to the eye.

Answer 18

1) Blood-ocular barriers
2) Plasma protein binding
3) Active transport

Question 19

Why is it difficult for systemic drugs to overcome the blood-aqueous barrier ?

Answer 19

It is limited due to the tight junctions (between capillary endothelial cells and RPE cells) and low permeability of iris blood vessels.

Question 20

How is the blood-aqueous barrier overcome?

Answer 20

Sometimes drug transporters are used.
Not all drugs can do this such as anti-VEGF.

Question 21

What is something a patient can do to maybe increase the absorption of a drug?

Answer 21

Put some pressure on the puncta after it has been administrated to give it a chance to be penetrated before it enters the nasolacrimal system.

Question 22

Are drugs indefinitely stable?

Answer 22

No

Question 23

What is a characteristic that is important in maintaining stability?

Answer 23

The pH of a drug- it retains solubility.

Question 24

Are corticosteroids lippophillic or hydrophilic?

Answer 24

Lippophillic.

Question 25

Once a multi dose bottle is open, what issues can come from this?

Answer 25

Oxidative damage and bacterial contamination.

Question 26

How is a drug sterilised ?

Answer 26

Heating the drug without impacting its stability and force the drug through a sterile filtration

Question 27

Once is a sterilised, what is put into a drug to ensure this is maintained?

Answer 27

Preservatives

Question 28

What group of drugs are preservative free?

Answer 28

Intraocular drugs

Question 29

Name six inactive ingredients which are used in ophthalmic formulations

Answer 29

-Buffers
-Preservatives
-Antioxidants
-Viscous agents
-Tonicity-adjusting agents
-pH adjusting agents

Question 30

What do viscosity agents do to a formulation?

Answer 30

Thicken it

Question 31

Name three antioxidants in drugs.

Answer 31

-EDTA
-Sodium bisulphite
-Sodium metabisulphite

Question 32

Name the function of preservatives

Answer 32

Destroy or inhibit the growth of micro-organisms

Question 33

Name three preservatives

Answer 33

• Benzalkonium chloride (BAK), this is the most common preservative used in ophthalmic drugs
• Phenylmercuric nitrate
  -Polyquad
• Newer less toxic include: Purite, Sofzia

Question 34

Name some properties of BAK (benzalkonium chloride)

Answer 34

• Can affect corneal penetration
• Binds to hydrogel CLs (can be problematic)
• Excellent chemical stability
• Effective against GM+ve and GM-ve organisms

Question 35

True or false: all preservatives are toxic.

Answer 35

True