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312 Eye/ENT/Dental/Pain > L3: Ocular delivery systems > Flashcards

L3: Ocular delivery systems Flashcards

1
Q

What are SIX routes of ocular administration?

A

Topical (99% of all drugs)
Intracameral (into anterior chamber, usually only after cataract surgery)
Intravitreal
Periocular (not into eye)
Suprachoroidal
Systemic (only 1% enters eye, so not very direct)

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2
Q

What are THREE transport barriers in the eye?

A

Tear film

Cornea

Blood-retina barrier

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3
Q

What are THREE drug characteristics to consider in absorption?

A

logP

pKa

Molecular weight

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4
Q

What are FOUR advantages of topical ocular delivery?

REDS

A

Rapid onset of action

Ease of application

Direct application to target site

Smaller drug dose required

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5
Q

What are FIVE disadvantages of topical ocular delivery?

A

Contamination of drops
Preservative may be needed –> may be added but can causes irritation eg. benzalkonium chloride
Limited penetration
Fast elimination
Systemic absorption –> side effects. Not effective for choroidal/back of eye infections

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6
Q

What is the cornea transport barrier?

A

Only small & lipophilic drugs can pass

Epithelium, stroma, endothelium
Lipophilic, hydrophilic, lipophilic

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7
Q

What are ocular solutions?

A

Homogeneous mixture composed of only one phase

Solute dissolved in solvent

eg. BBs, PGAs, AAs, CAIs, some antibiotics

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8
Q

What are THREE advantages of ocular solutions?

A

Good stability

Easy to prepare

Low cost

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9
Q

What are THREE disadvantages of ocular solutions?

A

Fast drainage –> does not last long on eye surface

Low drug permeability –> no concentration gradient since drop does not last long on eye surface

Low drug bioavailability –> due to corneal barrier

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10
Q

What are ocular suspensions?

A

Heterogeneous mixture composed of two phases

Solid phase dispersed through liquid base

eg. steroids

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11
Q

What are TWO advantages of ocular suspensions?

A

Longer retention time –> higher drug bioavailability

Reduced drainage –> drug remains in eye for longer

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12
Q

What are THREE disadvantages of ocular suspensions?

A

Sterilisation may cause physical instability

Particle size not <5 –> foreign body sensation –> reflex tearing

Particle aggregation/sedimentation –> must be shaken before use

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13
Q

What are ocular ointments?

A

Semisolid preparation intended for external application

Drug in hydrocarbon base (no water)

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14
Q

What are THREE advantages of ocular ointments?

A

High viscosity –> reduced drainage –> more likely absorbed

No stinging upon application –> eye drops stinging usually due to differences in pH

Oily base

  • No dilution by tears
  • No preservative required to prevent microbial growth
  • Suitable for moisture sensitive drugs
  • Lubrication
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15
Q

What are TWO disadvantages of ocular ointments?

A

Blurred vision –> application only at night

Greasy –> discomfort/irritation –> reflex tearing

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16
Q

What are ocular emulsions?

A

Heterogeneous mixture of two immiscible phases

Contains water, oil, surfactants/preservative –> caution irritation

17
Q

What are TWO advantages of ocular emulsions?

A

Suitable for oil-soluble drugs

Lubrication

18
Q

What are THREE disadvantages of ocular emulsions?

A

Surfactant –> irritation, local toxicity

Low stability –> flocculation leading to cracking, therefore dose not reliable

High cost

19
Q

What are FIVE formulation considerations?

POVIB

A

Physicochemical drug properties

  • Concentration
  • Lipophilicity
  • pH
  • Molecular weight
  • pKa

Osmotic pressure within 310-350 mOsm/kg

Viscosity –> allows drop to remain in eye longer for concentration gradient

Instillation volume –> eye max. 30 microlitres

Buffer capacity & pH –> best between pH7 - 7.7

20
Q

How does drug activation work? (metabolism)

A

eg. Prostaglandin analogues
Ester prodrugs –> more lipophilic –> crosses corneal epithelium more readily –> activation by esterases into active drug molecule

21
Q

How are drugs eliminated from the eye?

A

Nasolacrimal drainage –> also plug inner corner of eye to avoid systemic absorption & side effects

22
Q

How to administer eye drops that improves ocular bioavailability

A

Shake bottle before use (suspensions)

Apply one drop at a time, close eyes & block nasolacrimal duct

Wait 5 mins before next drop –> avoid washout effect for higher absorption

23
Q

What delivery systems improve ocular bioavailability?

A

Corneal penetration enhancers, prodrugs –> improve absorption

Viscosity enhancers, lubricating agents –> prolong concentration gradient

24
Q

In situ gelling of novel eye drops can be induced by…

A

Higher temperature in eye

Ions in tear fluid

pH of tear fluid

25
Q

The principle behind ocular iontophoresis is…

A

“like repels like”

Electrorepulsion “pushes” drug into tissue

312 Eye/ENT/Dental/Pain (9 decks)

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