Week 1.05 Drug Formation & Delivery Flashcards
To pass drug into eye:
- Mostly through the cornea
- Less than 20% via conjunctiva and sclera
- Cornea is a fat-water-fat sandwich
- Epithelium is lipophilic (fat soluble able to pass easily)
- Stroma is hydrophilic (water soluble able to pass)
- Endothelium is lipophilic
- Need to get through into anterior chamber so that it can affect receptors within iris of ciliary body
So, drug needs to be both fat and water soluble
What percentage of eye drop will reach the anterior chamber
~1%
Why is topical anaesthetic put in before cyclo
It increases the permeability of the cornea
More drug gets into site of action
Can use less drug to get same effect
What are some drug delivery systems
Multi dose dropper bottles
Single minums
Tubes
Impregnated strips
Periocular injection
Direct ocular injection - intracameral (anterior chamber), intravitreal
What does the pH of the drug need to be
Drugs need to be close to pH of tear fluid
~7.35. Ph of solutions used in eye normally 6 to 8
Are eyedrops hyper or hypotonic
Tend to be hypertonic
- higher ion conc
- outflow of fluid from the cornea
- corneal deturgescence
Hypotonic
- lower ion conc
Influx of fluid into cornea
Corneal oedema
What does the packaging of drugs need
Drug
Conc
Batch number
Date of manufacture
Exp date
High viscosity vs low
Low viscosity (aqueous solution)
- short term retention
- short term drug effect
- higher risk of systemic absorption (nasolacrimal)
- good vision
High viscosity (ointments)
- long term retention in eye
- long term drug effect
- Lower risk of systemic absorption (nano-lacrimal)
- poor vision
What’s the point of preservative
Defend the preparation from microbial contamination once the package has been opened
Benzalkonium chloride
Disrupts bacterial cell membranes
Minims
Single use
Approx 12 drops
Preservative free
Supplied in boxes of 20 applicators
Sterilised by autoclaving at 115 for 30 mins
