Pharmacokinetics

Question 1

What is pharmacokinetics?

Answer 1

The affect the body has on the drug

Question 2

Why is there limited treatment for ocular diseases?

Answer 2

Due to how well protected it is by ocular blood barrier

Question 3

What are the principles of pharmacokinetics?

Answer 3

1. Absorption
2. Distribution
3. Metabolism
4. Elimination

Question 4

Describe the oral route of drugs

Answer 4

1. metabolised in stomach
2. some absorption and some incomplete absorption by ileum
3. Via portal vein metabolised by liver
4. To heart via hepatic vein
5. systemic circulation
6. Drug distributed to be metabolised or eliminated/excreted

Question 5

Describe the systemic (IV) route

Answer 5

1. Systemic circulation
2. Drug distributed to be metabolised or eliminated/excreted

Question 6

What is the bioavailability of oral route?

Answer 6

Bioavailability= 0.05 to 1

Question 7

What is the bioavailability of intravenous route?

Answer 7

Bioavailability= 1

Question 8

How is topical drug absorbed?

Answer 8

Permeation across the cornea from tear film.
Non corneal durg - permeation across the conjunctiva and sclera into anterior uvea.

Question 9

Which route is best for topical drugs?

Answer 9

The cornea because the receptors are located beneath it

Question 10

How are topical drugs eliminated?

Answer 10

1. Blinking
2. Naso lacrimal route
3. Aqueous humour outflow

Question 11

What is the normal tear volume of the eye?

Answer 11

7-10 microlitres

Question 12

Why can some patients taste the eye drops after they are administered?

Answer 12

Some Pxs taste the eye drops due to nasolacrimal drainage. To avoid this tell them to put pressure on their puncta to avoid the drug going to the nose and to the mouth taste receptors

Question 13

Describe the route of topical drugs

Answer 13

1. absorbed through cornea and then into anterior chamber
2. diffusion into the blood circulation through anterior uvea
3. reaches aqueous humour to be easily distributed to the iris and ciliary body

Question 14

How does darker colour iris affect drug activity?

Answer 14

Drug molecules bind to melanin and create a reservoir, from which the drug is slowly released hence prolonging drug activity.

Question 15

How does drug elimination take place from anterior area?

Answer 15

1. The chamber angle and Schlemm’s canal
2. Blood flow in anterior uvea

Question 16

Why can’t topical drugs be used for the posterior segment?

Answer 16

1. Due to blood retinal barrier, the retinal pigmented epithelium has poor permeability so requires high systemic dose
2. The vitreous humour has high volume and viscosity so is a barrier from the front.

Instead will need to use intravitreous or periocular routes of injection

Question 17

What are the routes of drug adminstration?

Answer 17

1. Topical (For anterior segment)
2. Intraocular (intrvitreal injection)
3. Periocular (Subconjunctival route, Retrobulbar route, peribulbar route, Sub-tenon route)
4. Systemic (Oral and parenteral(routes other than GI tract))

Question 18

What are the advantages and disadvantages of Topical route?

Answer 18

Advantages:
1. Ease of application
2. Non - invasive
3. Drug localisation
4. good efficacy
5. low cost

Disadvantages:
1. Low ocular bioavailablity
2. Nasolacrimal drainage
3. epithelial barriers
4. not effective for posterior segment

Question 19

What are the advantages and disadvantages of intravitreal route?

Answer 19

Advantages:
1. 100% vitreal bioavailability
2. Effective retinal delivery
3. sustains delivery for up to 3 years
4. Bypasses multiple ocular barriers

Disadvantages:
1. Invasive
2. Patient inconvenience

Question 20

What are the advantages and disadvantages of periocular / suprachoroidal route?

Answer 20

Advantages:
1. Delivery to both anterior and posterior segments
2. less invasive than intravitreal

Disadvantages:
1. invasive
2. Clearance by circulation
3. Retinal pigment epithelial barrier for retinal delivery