Opthalmics Flashcards
What is the conjunctiva and corneal surfaces lubricated by?
- they are lubricated by a thin film of liquid (pre corneal tear film) secreted by the lacrimal glands
What are the additional components of tears?
0.7% protein, electrolytes and lysozyme
Why are tears necessary to the eye?
tears are necessary for the nutrition of the cornea, protection against bacterial infections, removal of cellular debris and foreign matter and the formation of a continuos film over the cornea to product a clear optical surface
What are the 3 layers of the pre corneal tear film?
1) Superficial oily layer
- consists of wax and cholesterol esters and it functions to slow evaporation
2) Middle aqueous layer - contains nutrients and lysozyme
3) adsorbed mucous layer- contains mucin and is involved in adhesion of the aqueous layer to the cornea which keeps the cornea wettable
What is the average tear volume?
7 microliters
What happens to most of the eyedrop when it is placed in the eye?
Goes through the lacrimal drainage system and systemic absorption of the components may occur through the membranes of the nasolacrimal duct
What can be done if systemic absorption of eyedrops is not desirable?
use a smaller drop size
What volume do normal dropper tips dispense?
provide about 25 micrometers but specialized tips can provide about 10 microliters
Topical ophthalmics must be manufactured as a _____
sterile product
What are the dose forms generally used in the eye?
Solutions, suspensions, gels, ointments, emulsions and some solid products
Describe ophthalmic solutions?
- drugs dissolved in an isotonic medium containing an antimicrobial preservative
- can be buffered but all products must be sterile
- administration via blunt dropper or a plastic container with a dropper tip
Describe ophthalmic gels?
contain a viscosity increasing agent in addition to the components used in a solution
- usually packaged in ophthalmic ointment tubes
Describe ophthalmic suspensions
- contain a suspending and sometimes dispersing agents
- suspended drug particles in the sub micron size range for ocular comfort, bioavailability and dispersibility
- most of the suspending agents are cellulose derivatives, high molecular weight polymers or surfactants
- care must be taken with surfactants to avoid irritation and disruption of the pre corneal tear film
Describe ophthalmic ointments
- contain micronized drug dispersed in a petrolatum or other non-aqueous base
- they are packaged in lined metal tubes or plastic-foil laminated tubes
Are there many or few preservatives available to those wanting to put a preservative in an ophthalmic product?
few
What is benzalkonium chloride commonly used with as a preservative?
- used in combination with EDTA to giver better activity against pseudomonas species
What are some of the benefits of benzalkonium chloride?
fast acting with good stability and wide spectrum of activity
- stable over wide pH and temperature ranges
- surfactant properties aid in corneal penetration of the drug
What is the usual concentration of benzalkonium chloride?
- usual concentration is 0.01% and should never exceed 0.02% as this will cause ocular discomfort
What does thimerosal have in it?
Mercury
When is thimerosal usually used?
when incompatibilities preclude the use of benzalkonium chloride
Is thimerosal fast acting or slow acting?
slow acting and may cause sensitization and toxicity
What is the usual concentration of thimerosal for ophthalmics?
0.01%
___ and ___ esters are used in combination and are most often used in ointments
methyl and propyl
What is the usual concentration of methyl and propyl esters?
methyl: 0.03-0.1%
propyl: 0.01-0.02%
pH of a solution with affect the chemical ___, ____ and _____
stability, solubility and ocular comfort
What are the 2 reasons that ocular comfort is important when selecting a buffer?
import for compliance and if the product is irritating the tearing that is associated will result in a decreased contact time
Buffer concentration should not exceed what value?
100 mM
What is the function viscosity increasing agents? What is commonly used?
- increase contact time, reduce drainage rate and enhance bioavailability
- methylcellulose derivatives, crabbers and polyvinyl alcohol are all commonly used
What do we want to tonicity of the ophthalmic product to be? Why do we want this?
- we want the product to be isotonic to avoid ocular discomfort (this can lead to poor compliance and washout)
What is generally used as a tonicity adjuster?
sodium chloride (sometimes glycerol or sugar is added)
What is the most common antioxidant in ophthalmic products? What other ones are used?
- sodium bisulfite
- other antioxidants used are acetylcysteine, ascorbic acid and sodium thiosulfate
Non ionic surfactants are the only type suitable for ophthalmic products- true or false
True
What is the general concentration range for surfactants?
0.1%
What is the most common base for ointments?
white petrolatum with mineral oil
sometimes liquid petrolatum/polyethylene combinations have been used
What are ophthalmic ointments typically preserved with?
they are typically preserved with parabens - those containing broad spectrum antibiotics do not require antimicrobial agents if the product meets an appropriate microbial challenge test
The USP preservative effectiveness test is not required for what products?
for anhydrous non-aqueous vehicles
List the antibacterial preservatives
benzalkonium chloride benzethonium chloride chlorobutanol phenylmercuric acetate phenylmercurinic nitrate thimerosal
List the antioxidants
sodium bisulfite
sodium metabisulfite
thiourea
ethylenediaminetetraacetic acid
List the wetting/clarifying agents
- polysorbate 80
- polysorbate 20
List the viscosity agents
- polvinyl alcohol
- polyvinylpyrrolidone
- methylcellulose
- hydroxypropyl methylcellulose
- hydroxyethylcellulose
