Ophthalmic Pharmaceutics Flashcards

1
Q

What type of opthalmic drugs are used to treat glaucoma?

A

Beta blockers, Carbonic anhydrase inhibitors, and prostaglandins.

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2
Q

How do pharmacokinetic properties of the eye differ from other organs?

A

1) Anatomical isolaton 2) Secluded access from systemic circulation -blood-retinal barrier -blood-aqueous barrier

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3
Q

How can ophtalmic medications be absorbed systemically?

A

Drug is absorbed from the nasal mucosa (following nasolacrimal drainage) and avoids first pass metabolism by liver.

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4
Q

How do opthalmic drug concentrations go down?

A
  • As you go deeper into layers (Tears > cornea > aqueous humor)
  • Tears dilute drug
  • Hydrophilic so doesn’t stay in tissues very well.
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5
Q

What are factors that are important for opthalmic drug delivery?

A
  • Amount of fluid that eye can hold
  • Corneal structure
  • Sclera and conjunctiva drug delivery
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6
Q

How much fluid can the eye hold?

A
  • Tear volume: 7-8 microliters
  • Unblinking eye: 30 microliters
  • Blinking eye: 10 microliters
  • Optimal drug volume: 20 microliters
  • 1 ggt to of opthalmic drug: 50 microliters
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7
Q

Explain the corneal structure.

A
  • Cornea has no blood vessels
  • Corneal layers
    • Epithelium: hydrophobic
    • Stroma: hydrophilic
    • Endothelium: hydrophobic
  • Multiple layers so hard to penetrate
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8
Q

How can you penetrate the cornea?

A

By making drugs with both hydrophobic and hydrophilic properties.

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9
Q

Explain the conjunctiva and sclera.

A
  • Conjunctiva
    • Vascularized
    • Epithelial tissue
  • Sclera
    • Collagenous
    • Porous matrix
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10
Q

What are some other factors affecting bioavailability?

A
  • Drop volume
    • Smaller, concentrated drops result in greater delivery
  • Lacrimal drainage (rapid drug loss tears)
    • Gels, ointments, and suspensions increase contact time
  • Punctual occlusion
    • decreased lacrimal drainage
  • Tears contain proteins
    • protein binding decreases bioavailability
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11
Q

Even more other factors affecting bioavailability?

A
  • Surfactant
    • increased surfactant = increased bioavailability
  • Concentration
    • increased concentration = increased drug flux
  • Viscosity
    • increased viscosity = increased contact time
  • pH
    • nonionized = increased epithelium absorption
    • ionized = increased stroma absorption
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12
Q

What are some sterility requirements?

A
  • Autoclave
  • Bacterial filters
  • Preservatives (benzalkonium chloride)
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13
Q

What are isotonicity requirements?

A
  • Eye is isotonic with 0.9% saline.
  • Hypertonic solutions: draws water to site of topical application
  • The eye is forgiving 0.6 to 2%
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14
Q

What are the pH or buffering requirements?

A
  • pH of the eye is 7.4
  • increased comfort
  • increased solubility
  • increased stability
  • increase bioavailability
  • maximize perservative efficiency
  • increases tear flow
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15
Q

What are the viscosity requirements?

A
  • Increased viscosity = increased contact time
  • Viscosity decreases with increase in temperature
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16
Q

What are the particle requirements?

A
  • Particle must be small enough to not cause irritation
  • Medication must not interact with perservative or buffering agents, which can create precipitation
  • Suspensions must redistribute medication with gentle shaking
17
Q

Why would we used alternative opthalmic dosage forms?

A
  • Reduce need for frequent dosing
  • Better facilitate drug absorption
  • To deliver drugs with limited solubility
  • To improve patient adherence
  • To treat severe infections
18
Q

What are alternatives to opthalmic solutions?

A
  • Opthalmic gel
  • Opthalmic ointments
  • Solid inserts
  • Contacts
  • Surgical implants
19
Q

What are the differences between solutions, gel-forming solutions, and suspensions?

A
20
Q

What type of drugs are most likely to penetrate the cornea surface?

A

Lipophilic drugs

21
Q

Can opthalmic ointments be heat sterilized?

A

No. But can add antibacterial agent.

22
Q

What is Ocusert?

A
  • pilocarpine
  • controlled rate over 1 week
  • placed inside the lower lid
23
Q

What is lacrisert?

A
  • A methylcellulose insert that dissolves inside the eye
  • Treatment of dry eye
  • Once daily use
24
Q
A