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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
How long will effective clearance take to clear eye drops?
4-23 minutes
26
What are the elimination routes?
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
27
What must topical ocular preparations be?
``` Isotonic Close to neutral pH Stable Sterile Particle free ```
28
If a topical ocular preparation is multi-dose what must it contain?
Preservative
29
What are the advantages of topical ocular preparations?
Easy for patient to use on their own Rapid onset of action Avoid hepatic metabolism
30
What must all ophthalmic preparations be?
Sterile
31
Why must they be sterile?
Ocular infections = vision loss
32
When can preservatives not be used?
Intraocular products
33
Which preservative is often used?
Benzalkonium chloride
34
Why have single dose units been developed?
To avoid the use of preservatives whilst maintaining product stability
35
What is problem with single dose units?
High manufacturing + packaging costs
36
What determines osmolarity?
Salt conc within lacrimal fluid
37
What do dry eye patients have?
Hypertonic lacrimal fluid
38
What do hypotonic solutions cause?
Oedema
39
What do hypertonic solutions cause?
Dehydration
40
What do hypotonic + hypertonic solutions both cause?
Irritation + induce tear production | = clears any applied solution
41
What ocular solution is tolerated well?
Osmotic pressure equal to 0.6-2% NaCl
42
What may be added to achieve isotonic solution?
Tonicity agents
43
What is the buffer capacity of lacrimal fluid?
Low
44
What is an acceptable pH for solution?
3.5 - 9
45
What happens if an agent is unstable at neutral pH?
Formulated at pH 4.5 as compromise
46
What are commonly used buffers?
Borate + phosphate
47
What is the lacrimal fluid tension?
43.6-46.6 mN/m at 37 degrees
48
What can happen if a solution has a lower surface tension?
Destabilise tear film + disperse lipid layer into droplets | = affect evaporation = irritation
49
Why are surfactants included?
Solubilise or disperse drugs
50
``` What happens to irritation potential down surfactant list? Cationic Anionic Zwitterionic Non-ionic ```
Decrease
51
What happens when you increase viscosity of solutions?
Prolong residence time = enhance drug absorption
52
What are examples of H2O-soluble polymers?
Hydroxypropylmethylcellulose Polyvinyl alcohol Polyethylene glycol
53
What happens if over viscosity limit?
Cause pain
54
What happens if very viscous solution?
Blurring | May block puncti + lacrimal canals
55
What are most ophthalmic preparations?
Solutions
56
What is design of solution?
Eye drop bottle = cheap to manufacture
57
Why are solutions homogenous?
Better dose uniformity
58
What is typical dose vol for solutions?
25-50 micro L
59
What is problem with solutions?
Cleared by drainage
60
What do ointments do?
Reduce clearance from eye
61
What are release profiles of ointments?
2-4 hrs
62
What can ointments be used for?
Poorly soluble drugs
63
What bases are used for the ointments?
Hydrophobic - paraffins | Hydrophilic - PEG
64
What are ointments used for?
Antibiotics Antifungals Steroids
65
What is problem with ointments?
May cause blurring
66
Describe gels
Semi-solid, H2O-soluble bases More suitable than ointments for H2O-soluble drugs Use polymers dispersed in liquid
67
What polymers do gels use?
OVA | Poloxamer
68
Describe ion-exchange resin
Drug ionically bound to an ion-exchange resin to form insoluble complex
69
How is drug released in ion-exchange resin?
Drug released from complex through exchange of drug ions in tear fluid
70
What factor in ion-exchange resin control rate of dug release?
Resin particle size
71
What are formulations?
Solutions Ointments Gels Ion-exchange resin

Pharmaceutics (21 decks)

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