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Flashcards in Drugs and the eye Deck (77):
1

list the 3 routes of administration of drugs

- topical
- intra-ocular
- systemic

2

list the 3 forms of topical routes of drug administration and describe each form

- solutions: for drugs which are soluble

- suspensions: for drugs which are not soluble e.g. steroid eye drops, which is a hydrophobic molecule, the suspension is an emulsion i.e. yo shake the bottle and this puts the molecule back into the solution

- ointments: used to increase the duration/content on the ocular surface, but can make vision smeary

3

list the 2 forms of intra-ocular routes of drug administration and describe each form

- injection: e.g. lucentis which treats AMD

- insert: drug is impregnated into insert and then into the vitreous where it is released over time e.g. steroids or antibiotics

4

list the 2 forms of systemic routes for drug administration

- oral
- injection

5

list the 7 pharmacological/therapeutic classes of drug and what the use/formulation of the drug depends on

- anti-invectives
- corticosteroids/anti-inflammatory
- anti-glaucoma
- dry eye
- mydriatics/cycloplegics
- local anaesthetics
- peri-operative

depending on the site of action will determine how to formulate the drug

6

what is drug bioavailability determined by

the unique pharmacokinetic properties of the eye

7

name 3 factors that influence the delivery of topical drugs to the eye

- pre-corneal factors e.g. tear film
- corneal penetration e.g. via cornea
- inside the eye

8

what does a single drop from a conventional dropper bottle exceed

the capacity of the conjunctival sac

9

what has a major influence of the drug on pre-corneal retention time

the tear turn over rate

10

what pre corneal component exceeds corneal penetration, what implication does this have and how can it be reduced

- nasolacrimal drainage
- higher rates of drainage occur with larger drop sizes and this is vulnerable to being systemically absorbed across the nasal mucosa causing systemic toxicity
- putting pressure on puncta after instillation can avoid/reduce systemic absorption

11

what part of the eye is the main route of entry for topical medication

the cornea

12

which form of drugs penetrate the corneal epithelium and endothelium rapidly

lipid soluble drugs

13

what part of the cornea limits the passage of lipophilic formulations of drugs

the hydrophilic stroma

14

what type of drugs contributes to optimal corneal penetration

drugs which possess a combination of hydrophilic and hydrophobic properties
e.g. a weak acid depending on the pH it is in

15

what can influence the rate of drug penetration

ocular morbidity

16

where are the drugs distributed, following corneal penetration/inside the eye

into the aqueous humour

17

what occurs with the drug in the aqueous humour (inside the eye)

drug-target interaction

18

how are drugs eliminated from the anterior chamber (inside the eye)

by a combination of aqueous turnover and absorption across the tissues of the anterior uvea

19

_______ binding can also influence bioavailability inside the eye

melanin binding can also influence bioavailability inside the eye

20

what 2 things are involved in drug-target interaction

- enzymes
- receptors

21

which enzymes are involved with drug-target interaction

carbonic anhydrase inhibitors e.g dorzolomide

22

give 2 example of drugs which bind to receptors during drug-target interaction

- beta blockers e.g. timolol
- muscarinic e.g. cyclopentolate

23

give 5 examples of enzymes that are involved in ocular drug metabolism

- esterases
- monoamine oxidase
- N-acetyltransferase
- oxidoreductase
- catechol-O-methyltransferase

24

where in the eye are drug metabolising enzymes usually found and what happens to the drug as it passes through this structure

in the cornea
as the drug passes through the cornea it is acted upon by these enzymes and transformed chemically through its transit

25

during drug metabolism, some drugs are broken down by ocular tissues during penetration ________________________

limiting their effectiveness

26

what are some pathways during drug metabolism exploited by

exploited by pro-drugs

27

how do pro-drugs exploit some pathways during drug metabolism

where the breakdown product is more efficacious than the parent compound e.g. the anti-glaucoma drug latanoprost is metabolised by esterases on the transit through the cornea

28

how are drugs excreted following corneal penetration and distribution

drugs are eliminated from the aqueous humour, by a combination of aqueous turnover and absorption across the tissues of the anterior uvea

29

what is an additional factor to drug excretion which can influence bioavailability and may predispose to toxicity

drug binding to the pigmented tissues of the iris and ciliary body

30

list 3 factors influencing systemic drug delivery to the eye

- blood-ocular barriers
- plasma protein binding
- active transport

31

how does plasma protein binding influence systemic drug delivery to the eye

as most drugs bind to plasma proteins which are big molecules that can't pass the barriers such as tight junctions at the blood/aqueous barrier or the iris blood vessels which are very tight

32

what does the blood aqueous barrier limit

the free access of systemic drugs to the anterior chamber

33

what are the main components of the blood aqueous barrier

the "tight" ciliary epithelium and low permeability of the iris blood vessels

34

what happens to the blood aqueous barrier when the eye is inflamed

the blood aqueous barrier can break down and increase drug bioavailability

35

what is the blood retinal barrier formed by

tight junctions between capillary endothelial cells and retinal pigment epithelial cells

36

what does the blood retinal barrier limit the passage of and name an exception

all the but the smallest lipid-soluble molecules
(thats why lucentis is injected into the eye)

37

what has been identified at the blood retinal barrier

several drug transporters

38

no drug is __________________

indefinitely stable

39

what should a drug ideally have

a long shelf life

40

what do some certain formulations of drugs require

specific storage conditions e.g. low temperature or absence of light

41

what may a soluble form of drug need and why

a specific pH to retain solubility

42

what can insoluble drugs be prepared as

suspensions

43

what is a drug subject to once opened if packaged as a multi dose bottle

oxidative damage and bacterial contamination

44

name some sterilisation method used on ophthalmic preparations

- heat
- sterile filtration (filters the bacteria out)

45

what are added to multi dose formulations of ophthalmic drugs in order to keep them sterile

preservatives

46

what type of ophthalmic drug is preservative free

intra-ocular products

47

what are excipients

inactive ingredients

48

name 6 excipients (inactive ingredients) used in ophthalmic formulations

- preservatives
- buffers
- antioxidants
- vicious agents
- tonicity-adjusting agents
- pH adjusting agents

49

what is the use for antioxidants in ophthalmic drugs

prevent or delay deterioration/breakdown of the drug by oxygen in the air

50

list 3 examples of antioxidants in ophthalmic drugs

- EDTA
- sodium bisulphite
- sodium metabisulphite

51

what is the use for preservatives in ophthalmic drugs

destroys or inhibits the growth of micro-organisms

52

list 4 examples of preservatives in ophthalmic drugs

- benzalkonium chloride (BAK)
- phenyl mercuric nitrate
- polyquad
- newer less toxic preservatives

53

which preservative is toxic to the ocular surface

benzalkonium chloride (BAK)

54

list 5 examples of the newer less toxic preservatives now available

- purite (stabilised oxychloro complex)
- sofzia (composed of boric acid)
- propylene glycol
- sorbitol chloride
- zinc chloride

55

what type of compound is benzalkonium chloride (BAK)

quaternary ammonium compound

56

benzalkonium chloride (BAK) is the most _________________

widely used preservative

57

which micro organisms is benzalkonium chloride (BAK) effective against

a wide range of GM +ve and GM -ve organisms

58

what concentration is benzalkonium chloride (BAK) available in

0.004 - 0.02%

59

benzalkonium chloride (BAK) has excellent ________ _______

chemical stability

60

benzalkonium chloride (BAK) can affect _____________ _____________

corneal penetration

61

what can benzalkonium chloride (BAK) not be used with and why

contact lenses as it binds to hydrogel lenses

62

list all the 6 things that the increased effect of preservatives has on the eye of people who use eyedrops for life/long term

- stinging or burning
- dry eye sensation
- tearing
- anterior blepharitis
- conjunctival follicles
- superficial punctate keratitis

63

what type of newer ophthalmic preservative is polyquarternium (polyquad)

a polymeric quaternary ammonium antimicrobial preservative

64

where is polyquarternium (polyquad) found

contact lens solutions and several artificial tear formulations

65

what has polyquarternium (polyquad) proven to have

less toxicity on corneal epithelial cells than BAK

66

what type of newer ophthalmic preservative is purite

a microbicide with a broad spectrum of antimicrobial activity

67

what does purite have very low toxicity to

mammalian cells

68

where does the preservative purite preserve the solution in and what happens to it following exposure to light

it preserves the solution in the bottle
but following exposure to light, is dissociates into water, sodium and chloride ions and oxygen

69

what is the use for buffers in ophthalmic drugs

it maintains the ophthalmic products in the pH range 6-8 which is the most comfortable for ophthalmic instillation

70

name two examples of buffers

- boric acid
- potassium bicarbonate

71

what is the use for viscous agents in ophthalmic drugs

increases contact time of the drug with the ocular surface by increasing viscosity of the preparation

72

name 3 examples of vicious agents

- methyl cellulose
- poly vinyl alcohol
- carbomers

73

what is the use for osmolarity adjusting agents

it creates an isotonic solution to improve comfort

74

what is the usual concentration of osmolarity adjusting agents

0.6 - 1.8%

75

name 2 examples of osmolarity adjusting agents

- mannitol
- NaCl

76

what is the use for pH adjusting agents

to create a pH that ensures optimal stability and tolerability

77

name 2 examples of pH adjusting agents

- hydrochloric acid
- sodium hydroxide