ophthalmic formulations Flashcards
what eye formulations can you get?
- eye drops/solutions
- eye ointments
- eye lotions
- sub-conjunctival injection; corticosteroids
what are the layers of the eye?
- outer layer
- segment of 2 spheres
- cornea; provides forward 1/6th
- sclera
what is the sclera?
tough fibrous tissue which protects the eye from the internal/external forces and maintains its shape alongside the intraocular pressure of eye
- > is back 5/6th of the globe
- > forms ‘white’ of the eye
what is the cornea made up of?
- innervated densely with sensory nerves
- refracts and transmits light to lens and retina
- protects eye against infection and structural damage to deeper parts
what does the conjuctiva do?
it is thin, transparent mucous membrane
covers the visible part of the sclera
- optic nerve emerges from sclera
what gland gives us tears?
the lacrimal gland
what do tears do for the eye?
lubricates the eye surface and protects it from chemical, microbes, airborne solid particles
what are the layers of the eye?
mucous layer; interacts with epithelial cells of cornea
aqueous layer; electrolytes, proteins, glycoproteins
superficial lipid layer; sterol esters, fatty acids and wax esters
what are the three chambers of the eye?
- anterior cavity
- posterior cavity
- vitreous cavity = 80% volume of the eye
where is the anterior and posterior chamber?
anterior; space between cornea and iris
posterior; space between iris and lens of your eye
what is the main routes for ocular drug delivery?
- cornea; drugs reach aqueous humour
- Blood retinal barrier; RPE-outerB and ECE-innerB
- > restricts drug entry from systemic circulation into posterior part of eye - intravitreal delivery route; directly reach back of eye
what are the drug elimination routes?
- elimination from aqueous humour into systemic uveoscleral circulation
- aqueous humour outflow through trabecular meshwork and schlemm’s canal
- from vitreous humour via diffusion into anterior chamber
- via posterior route across BRB
how efficient are hypotonic ophthalmic solutions for drug delivery?
- the corneal epithelium is more permeable so water can flow into the cornea; can lead to oedema
- it can be irritating to the eye and cause production of tears; not delivering anything
what are the methods of adjusting tonicity?
- freezing-point depression method
- sodium chloride equivalent method
- isotonic solution V-value method
what happens when acid/basic solutions are instilled in the eye?
- cannot be neutralised by tears
- so reflex tears are generated to dilute the administered drop and eliminate it
why is pH of formulation important?
important for drug ionisation and drug stability
- pH dependant hydrolytic degradation can occur
- maintains stability at 4-5 using weak buffer which allows lacrimal fluid to restore its normal pH
drug ionisation decreases solubility and so decreases permeability across corneal epithelium
main buffers used in ophthalmic preparations?
borate and phosphate buffers
how can viscosity be controlled in these preparations?
- viscosity enhancing polymers
- pro-long drug retention
- enhance drug absorption
- reduced drainage rate
- enhancers can drag water and stabilise aqueous layer
- increased volume= reservoir of drug
what are some viscosity-enhancing polymers?
- water soluble polymer
- polyvinyl alcohol
- cellulose derivatives
how should you consider Surface Tension with preparations?
solution should have lower ST than lacrimal fluid
- too high can destabilise the tear film
- disperses lipid layer into droplets that are solubilised by the drug or surfactant in formulation
what can be added for solubility of drug?
surfactant
can add non-ionic surfactants
-> can remove mucus layer and disrupt tight junctional cornea complexes :(
the conc. is important for drug solubility and safety and patient tolerance
what are the sterility requirements of the formulation?
the preparations must be sterile at time of filing and closing
- terminal sterilisation in final container preferred
- filtration under aseptic conditions is an option
- filter pore size of 0.22micrometres
- raw materials should be sterile
why are preservatives added?
- destroy and inhibit microorganisms growth
- should have broad spectrum anti-microbial activity
- exhibit stability and compatibility
- only for multi dose
- single dose units dont need preservatives
Labelling requirements for hospital ophthalmic preparations?
- volume of contents
- official name
- conc. of API
- name and conc of any added antimicrobial agent
- direction for use
- ‘sterile until opened’
- ‘use with care to avoid contamination during use’
- ’ to be discarded …days after first opening’
- storage requirement
- expiry date
- batch and product licence number
- POM or P
- patient name
- date of issue
- ‘for external use only’
- keep out of reach of children
- name and address of supplier
