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Pharmaceutics > Routes of Administration (Ocular) > Flashcards

Routes of Administration (Ocular) Flashcards

1
Q

What does the outer layer of the eye consist of?

A
  • Sclera
  • Cornea
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2
Q

What is the sclera?

A
  • Around most of eye
  • Tough, fibrous tissue
  • Protects eye and maintains shape
  • Front of sclera (white of the eye) covered by the conjunctiva (thin transparent mucous membrane) and lacrimal tears
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3
Q

What is the Cornea?

A
  • In front of iris and pupil
  • Has extensive sensory nerves
  • The surface is covered by tears from the lacrimal gland
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4
Q

What are the chambers of the eye?

A
  • 3 chambers: Anterior, posterior and vitreous
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5
Q

What is the anterior and posterior chambers?

A
  • Both in anterior segment (front of eye)
  • Filled with aqueous humour: colourless, with electrolytes, growth factors
  • If drainage from the eye is blocked, fluid and pressure accumulates leading to glaucoma
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6
Q

What is the vitreous chamber?

A
  • Contains vitreous humour (80% of the volume contains 98% hydrogel, 2% collagen fibrils and hyaluronic acid
  • Proteins, inorganic salts are present pH 7.5
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7
Q

What is the lacrimal gland?

A
  • The pre corneal tear film lubricates and protects the eye surface
  • It comprises 3 layers: Superficial lipid layer, Central aqueous layer (electrolytes, proteins), inner mucus layer
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8
Q

What is the pH of the tear film?

A
  • Normal tears : pH = 7.3-7.7
  • pH = lowest on awakening
  • Buffer capacity of the tears is determined by bicarbonate ions, proteins
  • Tears are more acidic in contact lens wearers. Alkaline in diseases
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9
Q

What is the blinking reflux?

A
  • Eye drops are administered, tear volume increased - this causes rapid blinking reflex. Essential for periodic reforming of tear film
  • Stop high speed foreign bodies approaching eye.
  • Blinking also activates a pumping mechanism for the draining of tears through the lacrimal drainage
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10
Q

What are the different drug delivery routes for ocular?

A

Delivery via
- Topical Cornea: main route –> reach aqueous humor (front0
- Periocular delivery –> By pass the conjunctival and corneal
- Intravitreal delivery –> Directly reach the back of the eye

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11
Q

What are the barriers to ocular delivery?

A
  • The lacrimal (tear) system continually washes eyes
  • Blinking causes fluid clearance
  • Maximum dose volume 20-30ul
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12
Q

What are the elimination routes of the ocular drug delivery?

A
  • Elimination from aqueous humor into systemic uveoscleral circulation
  • Outflow through trabecular meshwork and schlemm’s canal
  • Eliminate from vitreous humor via diffusion into anterior chamber
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13
Q

What do topical preparations need to be?

A
  • Isotonic
  • Close to neutral pH
  • Stable
  • Sterile
  • Particle free
  • Contain preservatives
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14
Q

What are some advantages of ocular route?

A
  • Easy for patient to administer on their own
  • Provides rapid onset of action
  • Avoid hepatic metabolism
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15
Q

Why does ocular preparations need to be sterile?

A
  • Ocular infections can lead to vision less
  • Preservatives must be included in multi dose containers (prevent going off) - inhibit microbial growth
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16
Q

Why does ocular preparations need to be isotonic?

A
  • Salt concentrations within the lacrimal fluid determines its osmolarity
  • Dry eye = hypertonic lacrimal fluid (dehydration)
  • Hypotonic causes oedema
  • Both cause eye irritation
17
Q

Why does ocular preparations need to have suitable pH?

A
  • pH of normal tears is close to neutral
  • Buffer capacity of lacrimal fluid is low. Extreme pH could damage
  • Can affect aqueous solubility and membrane permeability
18
Q

Why does ocular preparations need to consider surface tensions?

A
  • Ophthalmic solution with a lower surface tension can destabilise the tear film and disperse the lipid layer into droplets - can lead to evaporation and lead to irritation
19
Q

Why does ocular preparations need to consider viscosity?

A
  • Increasing the viscosity can prolong their residence time thus enhance drug absorption
  • Water soluble polymers used include: methylcellulose, polyethene glycol
  • Too high: higher force required for blinking
20
Q

What are the different types of opthalmic preparations?

A
  • Solutions: Simple designs/ bottle. Better dose uniformity. More rapidly cleared by drainage
  • Ointments: Reduce clearance from eyes. Used for poorly soluble drugs. Both hydrophilic and hydrophobic bases. Cause blurring
  • Gels: More better for water soluble drugs than ointments. Uses polymers
  • Ion exchange resins: Drug is ionically bound to an ion exchange resin –> forms an insoluble complex. Drug released from complex with exchange of drug ions with ions in tear fluids
21
Q

What are the different eye treatments?

A
  • Ocular Implants: Made from biodegradable/non- biodegradable polymers
  • Biodegradable intravitreal implant : treatment in posterior segment
  • Intracameral Implant: Reduce pressure in eye
  • Intravitreal Injections: Injecting into vitreous cavity

Pharmaceutics (12 decks)

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