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Pharmaceutics > Ocular Route > Flashcards

Ocular Route Flashcards

1
Q

What are tears produced by?

A

Lacrimal gland

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2
Q

What does the pre-corneal tear film do?

A

Lubricates + protects eye surface

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3
Q

What are the 3 layers in eye?

A

Superficial lipid layer
Central aq layer
Inner mucus layer

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4
Q

What does the superficial lipid layer do?

A

Reduce evaporation rate of tears

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5
Q

What does the inner mucus layer do?

A

Allows spread of tear film over eye surface on blinking

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6
Q

What is the pH of normal tears?

A

7.3-7.7

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7
Q

When is pH of the tears lowest?

A

On awakening

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8
Q

What can pH of tears vary from + why?

A

5.2-9.3 depending on age + disease

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9
Q

What are buffer capacity of tears determined by?

A

Bicarbonate ions
Proteins
Mucins

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10
Q

Why are tears more acidic in contact-lens wearers?

A

Impediment influx of CO2

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11
Q

When are tears more alkaline in case of disease?

A

Dry eye
Severe ocular rosacea
Lacrimal stenosis

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12
Q

What is the normal tear vol?

A

5.9 micro L

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13
Q

What is the max fluid vol in lower eyelid sack?

A

25-30 micro L

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14
Q

What is the rate of basal tear secretion?

A

1.2 micro L/min

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15
Q

What happens when eye drops are administrated?

A

Tear vol increases

= rapid reflex blinking

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16
Q

What is blinking?

A

Defence mechanism of eye

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17
Q

Why is brisk blinking reflex important?

A

Fast enough to proceed high-speed foreign bodies approaching eye

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18
Q

What does blinking activate?

A

Pumping mechanism for drainage of tears through lacrimal drainage apparatus

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19
Q

What is the blink rate?

A

17 per min

1 blink every 3.5s

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20
Q

What are the different ocular delivery routes?

A

Cornea
Periocular
Intravitreal

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21
Q

Describe cornea route

A

Main route for topically administered drugs to reach aq humour

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22
Q

Describe periocular route

A

By pass conjunctival + corneal epithelium

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23
Q

Describe intravitreal route

A

Directly reach back of eye

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24
Q

What are the barriers to ocular delivery?

A

Lachrymal (tear) system constantly washes eye
Blinking promotes fluid clearance
Max dose vol = 20-30 micro L

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25
Q

How long will effective clearance take to clear eye drops?

A

4-23 minutes

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26
Q

What are the elimination routes?

A

Aq humour into systemic uveoscleral circulation
Outflow through trabecular meshwork + Schlemm’s canal
Vitreous humour via diffusion into anterior chamber
Posterior route across blood retinal barrier

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27
Q

What must topical ocular preparations be?

A 
Isotonic 
Close to neutral pH
Stable
Sterile
Particle free
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28
Q

If a topical ocular preparation is multi-dose what must it contain?

A

Preservative

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29
Q

What are the advantages of topical ocular preparations?

A

Easy for patient to use on their own
Rapid onset of action
Avoid hepatic metabolism

30
Q

What must all ophthalmic preparations be?

A

Sterile

31
Q

Why must they be sterile?

A

Ocular infections = vision loss

32
Q

When can preservatives not be used?

A

Intraocular products

33
Q

Which preservative is often used?

A

Benzalkonium chloride

34
Q

Why have single dose units been developed?

A

To avoid the use of preservatives whilst maintaining product stability

35
Q

What is problem with single dose units?

A

High manufacturing + packaging costs

36
Q

What determines osmolarity?

A

Salt conc within lacrimal fluid

37
Q

What do dry eye patients have?

A

Hypertonic lacrimal fluid

38
Q

What do hypotonic solutions cause?

A

Oedema

39
Q

What do hypertonic solutions cause?

A

Dehydration

40
Q

What do hypotonic + hypertonic solutions both cause?

A

Irritation + induce tear production

= clears any applied solution

41
Q

What ocular solution is tolerated well?

A

Osmotic pressure equal to 0.6-2% NaCl

42
Q

What may be added to achieve isotonic solution?

A

Tonicity agents

43
Q

What is the buffer capacity of lacrimal fluid?

A

Low

44
Q

What is an acceptable pH for solution?

A

3.5 - 9

45
Q

What happens if an agent is unstable at neutral pH?

A

Formulated at pH 4.5 as compromise

46
Q

What are commonly used buffers?

A

Borate + phosphate

47
Q

What is the lacrimal fluid tension?

A

43.6-46.6 mN/m at 37 degrees

48
Q

What can happen if a solution has a lower surface tension?

A

Destabilise tear film + disperse lipid layer into droplets

= affect evaporation = irritation

49
Q

Why are surfactants included?

A

Solubilise or disperse drugs

50
Q 
What happens to irritation potential down surfactant list?
Cationic
Anionic
Zwitterionic 
Non-ionic
A

Decrease

51
Q

What happens when you increase viscosity of solutions?

A

Prolong residence time = enhance drug absorption

52
Q

What are examples of H2O-soluble polymers?

A

Hydroxypropylmethylcellulose
Polyvinyl alcohol
Polyethylene glycol

53
Q

What happens if over viscosity limit?

A

Cause pain

54
Q

What happens if very viscous solution?

A

Blurring

May block puncti + lacrimal canals

55
Q

What are most ophthalmic preparations?

A

Solutions

56
Q

What is design of solution?

A

Eye drop bottle = cheap to manufacture

57
Q

Why are solutions homogenous?

A

Better dose uniformity

58
Q

What is typical dose vol for solutions?

A

25-50 micro L

59
Q

What is problem with solutions?

A

Cleared by drainage

60
Q

What do ointments do?

A

Reduce clearance from eye

61
Q

What are release profiles of ointments?

A

2-4 hrs

62
Q

What can ointments be used for?

A

Poorly soluble drugs

63
Q

What bases are used for the ointments?

A

Hydrophobic - paraffins

Hydrophilic - PEG

64
Q

What are ointments used for?

A

Antibiotics
Antifungals
Steroids

65
Q

What is problem with ointments?

A

May cause blurring

66
Q

Describe gels

A

Semi-solid, H2O-soluble bases
More suitable than ointments for H2O-soluble drugs
Use polymers dispersed in liquid

67
Q

What polymers do gels use?

A

OVA

Poloxamer

68
Q

Describe ion-exchange resin

A

Drug ionically bound to an ion-exchange resin to form insoluble complex

69
Q

How is drug released in ion-exchange resin?

A

Drug released from complex through exchange of drug ions in tear fluid

70
Q

What factor in ion-exchange resin control rate of dug release?

A

Resin particle size

71
Q

What are formulations?

A

Solutions
Ointments
Gels
Ion-exchange resin

Pharmaceutics (21 decks)

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