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Pharmaceutics 2 Winter Final > 3 - Ocular > Flashcards

3 - Ocular Flashcards

1
Q

What is the benefit to microparticles in ocular products?

A

Encapsulate the drug and provide sustained release for prolonged times at target site

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2
Q

What is the benefit of chitosan for ocular preparations?

A
  • Is a polycation, so binds to mucin (polyanion) via ionic interaction between primary amino groups (chitosan) and sialic and sulphonic acid substructures of glycosylated chains of mucins
  • Hydroxyl and amino groups of chitosan may interact w/ mucin via H bonds
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3
Q

What does successful drug tx of various eye diseases depend on?

A
  • Intrinsic activity of drug
  • Ability of drug to cross biological barriers
  • Maintenance of drug in lachrymal fluid for an extended period of time
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4
Q

Why is the eye difficult to study?

A

Isolated, highly protected organ

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5
Q

What are the 3 primary modes of drug delivery to the eye?

A
  • Topical application to surface
  • Administration to eye for absorption into eye
  • Direct injection into eye (only done by trained professionals)
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6
Q

Are eye products for systemic absorption common? What do they depend on?

A
  • No

- Depends on lachrymal drainage and subsequent systemic absorption

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7
Q

What are the objectives of ocular drug delivery?

A
  • Retain drug formulations on the site of action for an extended period of time
  • Achieve maximal local therapeutic outcomes while minimizing systemic effects
  • Reduce drug irritability or any other adverse effects to their minimal levels
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8
Q

What are the physiological barriers of the eye?

A
  • Tear turnover
  • Naso-lachrymal drainage
  • Blinking
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9
Q

What are the anatomical barriers of the eye?

A
  • Static barriers which limit drug entry to anterior chamber (corneal epithelium, stroma, and blood-aqueous barrier)
  • Dynamic barriers which are involved w/ drug clearance (conjunctival blood and lymph flow, tear drainage)
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10
Q

What is mucin? What is its function?

A
  • Gel-like structure
  • Protective role into the eye
  • Permeation barrier which restricts ocular drug absorption
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11
Q

Why is only a small portion of topically instilled eye preparations absorbed?

A
  • Precorneal loss
  • Physiological and anatomical constraints
  • Also solution drainage, lacrimation, tear turnover, tear dilution, and conjunctival absorption
  • Low permeability of corneal epithelial membrane
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12
Q

What must be achieved for ocular permeability?

A

Balance of lipophilicity and hydrophilicity

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13
Q

What is the volume of precorneal fluid?

A

7-10 uL

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14
Q

What are the factors that influence drainage rate?

A
  • Instilled volume (higher volume = faster drainage)
  • Viscosity (increasing extends residence time in conjunctival sac)
  • pH (instillation of acidic or alkaline solution results in tear secretion and loss of drug, so adjusted to 7-7.7)
  • Tonicity (should be isotonic
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15
Q

Which drugs affect tear production and what is the effect?

A
  • Epinephrine induces tear production

- Local anesthetics (ex: tetracaine) suppress it

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16
Q

What percent of tear fluid is protein? What is the effect of drug binding to tear proteins?

A
  • 0.7% protein

- Drug binding results in reduction of total free rug available for action at target site

17
Q

What are the layers of the cornea?

A
  • Epithelial layer (lipophilic drugs penetrate through transcellular diffusion; paracellular diffusion limited to MW less than 100)
  • Bowman’s layer
  • Stroma (hydrophilic, so hydrophilic molecules traverse easily and lipophilic molecules have difficulty)
  • Descemet’s membrane
  • Endothelial layer (innermost; relatively porous allowing hydrophilic and lipophilic molecules through)
18
Q

Where does melanin binding occur in the eye? Which drugs have high binding capacity for melanin? How does this affect release rate?

A
  • Iris and ciliary body
  • Ephedrine and timolol
  • Only a small portion of bound drug is released at a very slow rate
19
Q

Where are enzymes found in the eye?

A

Ocular tissues (cornea, lens, iris-ciliary body, retina)

20
Q

Most of the dose forms for the eye are useful for _____

A

Delivering drug to anterior portion of eye which includes cornea, anterior chamber, iris, and lens

21
Q

What makes it difficult to treat ocular tissues through systemic administration?

A

Blood-eye barrier (BEB), similar to BBB

22
Q

What happens to drug that isn’t lost to lacrimal drainage?

A

Permeates mucous membranes of conjunctiva and is lost to systemic absorption before it can enter inner ocular tissues

23
Q

Usually ____ of the applied dose is available to the posterior portion of the eye for absorption

A

Less than 5%

24
Q

How can absorption occur across the cornea?

A

Transcellular and paracellular pathways

25
Q

Can polar hydrophilic drugs permeate the cornea?

A

Not well b/c of tight junctions between cells

26
Q

Can lipophilic drugs permeate the cornea?

A
  • Can pass through epithelial membrane

- Underlying stroma is hydrophilic and a major barrier to permeation

27
Q

What can be done to enhance ocular absorption? What are drawbacks to these methods?

A
  • Increase drug concentration to decrease volume instilled so less stimulation of lacrimal glands and less tear washout; drawback is solubility of the drug and problems w/ hypertonicity
  • Pro-drugs to enhance absorption by increasing lipophilicity of molecule
  • Bioadhesives and absorption enhancers
  • Cyclodextrins
  • Absorption promoters
28
Q

What do bioadhesives do?

A

Form weak bonds w/ conjunctival membrane or mucin layer of tear film to prolong contact time

29
Q

What do cyclodextrins do for ocular products?

A
  • Allow higher drug concentration at cornea
  • Confer greater stability to many drugs
  • Decrease local irritation
  • Have affinity for membranes
30
Q

What are examples of absorption promoters for ocular products?

A
  • Bile salts, surfactants, and chelating agents

- Benzalkonium chloride (common preservative) also enhances absorption through regulating tight junctions

31
Q

How do absorption promoters work?

A
  • Fluidizing phospholipid bilayer

- Opening tight junctions between cells by binding calcium

32
Q

What does the Lacrisert insert do? What is its benefit?

A
  • Stabilizes and thickens precorneal tear film and prolongs tear film breakup time in px w/ dry eye states
  • Usually reduces sx resulting from dry eye syndromes

Pharmaceutics 2 Winter Final (9 decks)

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