ocular drug delivery Flashcards
what are the different layers of the eyes
outer - sclera and cornea
middle- iris, ciliary body and choroid
inner - retina
chambers - anterior and posterior, vitreous cavity
what are the barriers to topical ocular ddel
pre-corneal factors
- solution drainage, blinking, tear film, tear turnover
- induced lacrimation
- mucin in tear film is hydrophobic
anatomical
- layers of cornea, conjunctiva and sclera
what are the barriers to systemic ocular ddel
blood aqueous barrier
blood retinal barrier
why is the blood retinal barrier a barrier to systemic ocular ddel
requires specific targeting systems, limited access requires high oral doses
what considerations need to be made when developing drugs for ocular delivery
osmolarity
pH
surface tension
viscosity
why does osmolarity need to be considered when developing drugs for ocular delivery
determined by concentration of lacrimal fluids - 0.9-1%
hypotonic cause oedema, hypertonic dry the corneal epithelium
why does pH need to be considered when developing drugs for ocular delivery
important in controlling ionisation and corneal permeability (6.9-7.5)
why does surface tension need to be considered when developing drugs for ocular delivery
drops that lower the surface tension of the eye
- destabilise tear film
- disperse lipids into droplets
- solubilised by drug/surfactants in formulation
why does viscosity need to be considered when developing drugs for ocular delivery
to prolong retention in tear film
PVP, PVA, MC, HPMC
blinking force limits viscosity
what are the advantages and disadvantages of using solutions for topical ocular ddel
easy and cheap
rapid onset of action with good dose uniformity
rapidly drained from the eye - proportional to drop size
variations in amount dispensed
why are suspensions used for ocular ddel
administration of soluble aqueous drugs - steroids and to prolong release
why are gels used in ocular ddel
semi-solid with water soluble base - polymers dispersed in liquids
can be activated to undergo phase transition in the eye
what are the 3 routes of systemic/direct ocular ddel
intracameral - anterior chambers
intravitreal
periocular (subconjunctival, retrobulbar and peribulbar)
what are the advantages and disadvantages of intravitreal injection for ocular ddel
Distribution in vitreous is non-uniform – LMW can rapidly distribute, HMW cannot
Best way to deliver but poor compliance
Drug retention requires frequent administration
what are punctual plugs
plugs inserted into tear ducts that release drugs over 1-2m
what are the two types of implant for ocular ddel
- Fluocinolone over 3 yrs – non-bioerodible
- Latanoprost, subconjunctival space, 3m as is bioerodible
what is iontophoresis and how is it used in ocular ddel
- The basic electrical principle that oppositely charged ions attract and same charged ions repel is the central tenet of iontophoresis.
- The ionized substances are driven into the tissue by electrorepulsion at either the anode (for positive drug) or the cathode (for negatively charged drug)
- ocular iontophoresis is capable of delivering substantially higher ocular drug concentrations than traditional topical applications, leading to greater bioavailability and more sustained therapeutic effect and reducing the frequency of dosing
what are drug eluting contact lenses
drug coated on or imprinted on inner side of lenses – provides steady drug release
what are topical ophthalmic drug delivery devices
- device floats on the sclera under eyelid
- 3-90 days of delivery
- Human clinical trials
what is triggerfish
- Contact lens providing constant IOP readings
- Sensor contains strain gauges that measure corneal curvature changes caused by intraocular pressure variations
