Ocular Route Flashcards
Ocular route is..
administration via the eye
what does the pre-corneal tear film do?
lubricates and protects the eye surface
the pre-corneal tear film consists of what layers? (3)
superficial lipid layer
- sterol esters, wax esters and fatty acids to reduce evaporation rate of tears
central aqueous layer
- electrocytes, proteins, biopolymers, urea
inner mucus layer
- allows spread of tear film over the eye surface on blinking
pH of normal tears is…
Diseased..
7.3-7.7
diseases - 5.2 - 9.3
pH of tears upon awakening?
lowest
Who has more acidic tears?
More alkaline?
contact-lens wearers more acidic due to impediment of the efflux of co2
alkaline in case of diseases such as dry eye
Human tear volume..
5-9uL
Maximum amount of fluid that can be held in lower eyelid sack..
25-30uL
Basal tear are secreted at…
1.2 uL per minute
What is blinking?
An important defence mechanism of the eye.
Essential for periodic reforming of the tear film.
Activates a pumping mechanism for the drainage of tears through the lacrimal drainage apparatus.
Blink rate in humans at rest..
17 per minute
Delivery can be via (3)
cornea - main route
periocular
passing the conjunctival and corneal epithelium
intravitreal
directly reach the back of the eye
Barriers to ocular local delivery: (3)
tear system constantly washed the eye
blinking promotes fluid clearence
maximum dose volume 20-30uL
Ophthalmic preparations include… (4)
solutions
simple design, cheap, homogenous dose between 25 to 50 uL
ointments
reduce clearing, may cause blurring. used for poorly soluble drugs, hydrophobic and hydrophilic
gels
semi-solid, water soluble base so more suitable than ointments for water soluble drugs
ion-exchange resins
drug is ionically bound to an ion-exchange resin to form an insoluble complex. released through exchange of drug ions with ions in tear fluids
Formulation considerations
Sterility
must be sterile or infections could lead to vision loss
preservatives must be included in multi-dose containers to inhibit microbial growth e.g. benzalkonium chloride
single dose units developed
Formulation considerations
Tonicity
salt concentration within the lacrimal fluid determines its osmolarity
hypotonic cause oedemaa
hypertonic cause dehydration
= both cause irritation and induce tear production
Formulation considerations
pH
pH range of 3.5 to 9, extreme pH could damage ocular tissue
Formulation considerations
Surface Tension
surfactants included to solubilise or disperse drugs and decrease irritation portenial
lower surface tension can destabilise the tear film and disperse the lipid layer into droplets
Formulation considerations
Viscosity
increasing viscosity of solutions can prolong their residence time thus enhance drug absorption
over the viscosity limit (0.9N) would cause pain / cause blurring.
Eye drops must be:
easy to use
rapid onset of action
close to neutral pH, stable, sterile, particle free
Elimination routes
from aqueous humour into systemic uveoscleral circulation
outflow through trabecular meshwork and Schlemm’s canal
from vitreous humour via diffusion into anterior chamber
via posterior route across blood retinal barrier.
