Ophthalmic Pharmaceutics Flashcards
What type of opthalmic drugs are used to treat glaucoma?
Beta blockers, Carbonic anhydrase inhibitors, and prostaglandins.
How do pharmacokinetic properties of the eye differ from other organs?
1) Anatomical isolaton 2) Secluded access from systemic circulation -blood-retinal barrier -blood-aqueous barrier
How can ophtalmic medications be absorbed systemically?
Drug is absorbed from the nasal mucosa (following nasolacrimal drainage) and avoids first pass metabolism by liver.
How do opthalmic drug concentrations go down?
- As you go deeper into layers (Tears > cornea > aqueous humor)
- Tears dilute drug
- Hydrophilic so doesn’t stay in tissues very well.
What are factors that are important for opthalmic drug delivery?
- Amount of fluid that eye can hold
- Corneal structure
- Sclera and conjunctiva drug delivery
How much fluid can the eye hold?
- 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
Explain the corneal structure.
- Cornea has no blood vessels
- Corneal layers
- Epithelium: hydrophobic
- Stroma: hydrophilic
- Endothelium: hydrophobic
- Multiple layers so hard to penetrate
How can you penetrate the cornea?
By making drugs with both hydrophobic and hydrophilic properties.
Explain the conjunctiva and sclera.
- Conjunctiva
- Vascularized
- Epithelial tissue
- Sclera
- Collagenous
- Porous matrix
What are some other factors affecting bioavailability?
- 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
Even more other factors affecting bioavailability?
- 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
What are some sterility requirements?
- Autoclave
- Bacterial filters
- Preservatives (benzalkonium chloride)
What are isotonicity requirements?
- Eye is isotonic with 0.9% saline.
- Hypertonic solutions: draws water to site of topical application
- The eye is forgiving 0.6 to 2%
What are the pH or buffering requirements?
- pH of the eye is 7.4
- increased comfort
- increased solubility
- increased stability
- increase bioavailability
- maximize perservative efficiency
- increases tear flow
What are the viscosity requirements?
- Increased viscosity = increased contact time
- Viscosity decreases with increase in temperature
What are the particle requirements?
- 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
Why would we used alternative opthalmic dosage forms?
- Reduce need for frequent dosing
- Better facilitate drug absorption
- To deliver drugs with limited solubility
- To improve patient adherence
- To treat severe infections
What are alternatives to opthalmic solutions?
- Opthalmic gel
- Opthalmic ointments
- Solid inserts
- Contacts
- Surgical implants
What are the differences between solutions, gel-forming solutions, and suspensions?
What type of drugs are most likely to penetrate the cornea surface?
Lipophilic drugs
Can opthalmic ointments be heat sterilized?
No. But can add antibacterial agent.
What is Ocusert?
- pilocarpine
- controlled rate over 1 week
- placed inside the lower lid
What is lacrisert?
- A methylcellulose insert that dissolves inside the eye
- Treatment of dry eye
- Once daily use
