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Pharmacology II > Ocular pharmacology and therapeutics > Flashcards

Ocular pharmacology and therapeutics Flashcards

1
Q

What is the major driving force for a drug moving through the anatomy of the eye?

A

Passive diffusion; concentration dependent

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2
Q

How long will a drug remain on the cornea/in the tear film?

A

Just a few minutes

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3
Q

About what is the standard lacrimal flow/production per minute?

A

15%/minute or 1ul/min

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4
Q

What is the normal lacrimal volume? What is it expanded to at most?

A

7ul; 25-30ul

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5
Q

How big is the average drop size?

A

40-75ul

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6
Q

Describe the drainage pathways for lacrimal outflow

A

80% to nasolacrimal drainage
Some to conjunctival vessels (Inflammation increases this)
Blinking pumping out tears

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7
Q

What effect does punctal occlusion have on tear drainage?

A

Slows it, allows for much greater corneal absorption of a drug

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8
Q

How does increasing protein concentration in the tears affect drug absorption?

A

Decreases it due to increasing protein binding of the drug

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9
Q

How is corneal contact time related to drug absorption and tear turnover?

A

Longer corneal contact, more drug absorption. Longer corneal contact generally decreased tear turnover

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10
Q

How does dry eye affect drug absorption?

A

Lower tear layers, less tear volume, less turnover –> more corneal contact time
Unless dry eye is causing increased lacrimation

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11
Q

How does CL wear affect drug absorption?

A

If comfortable then really no effect, if not then can cause lower contact time. Can put a drop and secure with a CL in place

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12
Q

How do local anaesthetics affect drug absorption?

A

Tend to damage epithelium and remove it, allowing for better drug absorption

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13
Q

What is the major barrier to drug absorption in the eye?

A

Corneal epithelium

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14
Q

What effect does age have on drug absorption?

A

Variable. Older may have droopy eyelids and slower turnover time with great corneal contact time.

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15
Q

What effect does punctal occlusion have on drug absorption?

A

Increases it

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16
Q

With a weak acid in pH below its pKa, it will be ionized or nonionized?

A

Nonionized - Too many protons to give up charge

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17
Q

With a weak acid in pH above its pKa, it will be ionized or nonionized?

A

Ionized - Giving up proton due to solution being deficient

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18
Q

With a weak base in pH below its pKa, will it be ionized or nonionized?

A

Ionized - Many protons, will have its own

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19
Q

With a weak base in pH above its pKa, will it be ionized or nonionized?

A

Non-ionized - Not enough protons

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20
Q

To be water soluble a molecule must be ionized or nonionized?

A

Ionized

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21
Q

To be lipid soluble a molecule must be ionized or nonionized?

A

Nonionized

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22
Q

If an acid is in solution that is 1pH above its pKa then what ratio of ionized to nonionized form will be present?

A

9:1 ionized to nonionized

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23
Q

If an acid is in solution that is 2pH above its pKa then what ratio of ionized to nonionized form will be present?

A

99:1 ionized to nonionized

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24
Q

If you disrupt the corneal epithelium, what happens to drug absorption?

A

Increases

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25
Q

What can you apply to disrupt the epithelium?

A

Benzalkonium chloride

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26
Q

What condition can increase drug absorption on the cornea?

A

Inflammation, diffuse keratitis better than a localized ulcer

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27
Q

How can an inflammed conjunctiva affect drug absorption?

A

Can increase absorption, but if it’s located away from the cornea then less drug absorption as it ends up in the systemic absorption not corneal

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28
Q

What are the advantages for a solution based administration?

A

Easy to do
Rapid absorption
Homogeneous
VA unaffected

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29
Q

What are the disadvantages for a solution based administration?

A

Shortest contact time

Accuracy of administration

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30
Q

What are the advantages of a suspension based administration?

A

Longer contact time

31
Q

What are the disadvantages of a suspension based administration?

A

Bioavailability
Non-homogeneous (Must remix)
Foreign body sensation

32
Q

Why would you use an ointment administration?

A

Deliver a very lipid soluble drug without irritation that a suspension can cause

33
Q

What are some advantages of an ointment administration?

A

Longest contact time
Increased stability
Less risk of contamination

34
Q

What are some disadvantages of an ointment administration?

A

Affects VA
Bioavailability
Higher risk of allergy
Harder to administer

35
Q

Increasing the viscosity of a solution has what effect on drug contact time?

A

Increases it; use methylcellulose or polyvinyl alcohol

36
Q

What effects can viscosity have on a drop?

A

Ups absorption time, contact time but also blinking

Makes the drop size too large, so can decrease volume and increase compensation to match

37
Q

What’s washout?

A

When a drug is administered and then another drop of drug or something else is put in shortly after, will remove the initial drug

38
Q

Which to put in first, an ointment or a drop?

A

Drop most likely as the ointment can increase the lipid layer which makes it harder to absorb

39
Q

Describe the preservative benzalkonium chloride

A

Used in most drops, can disrupt epithelium that helps absorption but is bad overall to the eye

40
Q

Describe the discontonued preservative thimerosal

A

Caused allergic like reactions at a high rate (not an actual allergy though)

41
Q

What does a preservative actually do?

A

Does not ‘keep’ the drop working, rather it is antibacterial to prevent contamination

42
Q

A drug that is hypertonic may be better for treating what?

A

Corneal edema, suck up the eye

43
Q

Describe the effects pH and temperature can have on a drug

A

pH can either stabilized or destabilize the drug, if nonionized tend to be less stable (most drops we use are weak bases)
Higher the temperature, less stable a drug is generally speaking

44
Q

Describe the reservoir technique

A

Placing a thick gel on lids/lashes so drug can soak in through the lids and lashes into the eye

45
Q

Name the lid scrubs we tend to use

A

Pilopine H.S. (gel)
Timoptic-XE
“Gelrite”

46
Q

What problem can happen from lid scrubs?

A

Toxicities due to high drug concentrations

47
Q

Describe a cotten pledget

A

Cotton soaked drug, can cause a teardrop dilation

48
Q

What is a teardrop dilation?

A

Seen with a cotten pledget soaked in a mydriatic and the inferior iris will dilate before the superior, a partial dilation

49
Q

Describe a Lacrisert

A

A chunk of hydroxypropylcellulose with drug in lower cul-de-sac for very long absorption, doesn’t always dissolve

50
Q

What is the Ocusert?

A

Very sophisticated drug delivery system for a few weeks, but very expensive. But it was very close to the ideal

51
Q

What determines the steady state of a drug?

A

Dose, frequency and half-life

52
Q

Changing the frequency of administration has what effect on steady state?

A

Stabilizes it, less fluctuations

53
Q

Changing the concentration of a drug dose has what effect on steady state?

A

Affects peak concentrations

54
Q

What concerns can happen with systemic medications versus topical?

A

Absorption from GI, first pass effect, drug stability
Increased risk of toxicities
But good for chronic management

55
Q

What are the periocular injection sites?

A

Subconjunctival
Subtenon
Retrobulbar

56
Q

What are the intraocular injection sites?

A

Intracameral

Intravitreal

57
Q

Which are the most permeable blood vessels?

A

Uveal; damage due to inflammation causes drug drainage

58
Q

What is the single best way to prevent toxicities in patients?

A

Good patient selection

59
Q

What kinds of factors must be considered in patient selection?

A

Existing medications
Allergies
Systemic conditions

60
Q

What tests are affected by drugs like topical mydriatics?

A 
VA and Refraction
Pupil evaluation
Amplitude of accommodation
Binocularity
Slit Lamp/Tear FIlm
Blood Pressure
Tonometry
Anterior Chamber (phenylephrine can cause pigment dispersion)
61
Q

What are the two kinds of adverse reactions to drugs?

A

Toxic and allergic

62
Q

Describe toxic reactions

A

Predictable extensions of the pharmacologic effects. Can be severe but infrequent

63
Q

Describe allergic reactions

A

Unpredictable and unlikely. Related to previous exposure and can be anaphylactic (immediate) and possibly become systemic

64
Q

What are the kinds of toxicities?

A

Drug toxicity - Direct toxic effect of the drug
Allergic - Acquired after repeated exposure
Idiosyncratic - Genetic predispostion
Hyperreactivity
Tolerance and drug/drug interactions
Placebo Effect

65
Q

An anaphylactic reaction is a

A

Immediate toxic reaction; emergency and can be signaled with urtricia and pruritis (hives and itching)

66
Q

What kind of anaphylactic reactions can occur with the lungs?

A 
Laryngeal edema
Bronchospasm
Air hunger
Tachycardia
Wheezing
67
Q

What kind of anaphylactic reactions can occur with the circulation?

A

Hypotension

Collapse due to no flow to brain (Syncope)

68
Q

How do you manage anaphylactic reactions?

A

EPINEPHRINE INJECTION with supplemental oxygen

69
Q

What is cardiopulmonary arrest?

A

The biggest emergency possible from an anaphylactic reaction

70
Q

What are some factors that can increase toxicities?

A

Drug concentration
Sometimes route of administration (systemic/injection tend to have higher risk)
Systemic disease
Previous history of allergies or idiosyncratic reactions

71
Q

What can you try to do to lower toxicity risk?

A

Keep drugs from kids
An ointment tends to have less effects
A lower dose for the shortest time possible (Lower still in kids)
Inflamed conjuctiva requires gentle administration
Use drug only as directed
Light irises tend to absorb drug easier
Topical LA’s will increase drug absorption
Enivornmental conditions
Punctal occlusion

72
Q

1% drug concentration is what mg/ml?

A

10mg/ml

73
Q

About how many drops are in an eye drop bottle?

A

20 drops

74
Q

If a bottle is 1% concentration and about how much drug is in each drop?

A

0.5mg/ml (1% is 10mg/ml, divide by 20 drops in a bottle)

Pharmacology II (10 decks)

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