Section 8 - Ophthalmics Flashcards
What is an ophthalmic product?
Sterile dosage form free from foreign particles suitably compounded and packaged for instillation into the eye
Which dosage forms can ophthalmic products be?
Solutions, suspensions, ointments, emulsions, and some solid
What is the conjunctiva?
Membrane covering outer surface of the white portion of the eye and inner surface of eyelids
Which gland secretes tear film?
Lacrimal glands
What are tears made up of?
0.7% protein, electrolytes, and lysozyme
What is the purpose of tears?
- Nutrition of cornea
- Protection against bacterial infections
- Removal of cellular debris and foreign matter
- Formation of a continuous film over the cornea to produce a clear optical surface
How long does it take for tears to evaporate?
15-30 seconds
What are the 3 layers of the precorneal tear film and what is the function of each?
1) Superficial oily layer - consists of wax and cholesterol esters and slows evaporation
2) Middle aqueous layer - contains nutrients and lysozyme (thickest layer)
3) Adsorbed mucus layer - contains mucin and involved in adhesion of aqueous layer to cornea which keeps cornea wettable
What is the average tear volume?
7 uL
What occurs when tear volume is increased by instillation of an eyedrop?
Rapid reflex blinking restores volume back to normal
When an eyedrop is instilled, where does most of it go?
Through lacrimal drainage system and systemic absorption may occur through the membranes of the nasolacrimal duct
What can be done if nasolacrimal absorption is undesirable?
Use a smaller drop size
What volume do normal dropper tips provide?
25 uL
What makes topical ophthalmics different from topical skin products?
Topical ophthalmics must be manufactured as a sterile product and steps taken to ensure sterility
What is the drug dissolved in in an ophthalmic solution?
Isotonic medium containing antimicrobial preservative
When would an antimicrobial preservative not be needed in a ophthalmic solution?
If unit dose packaging is used
What do gel ophthalmics contain?
Viscosity-increasing agent in addition to the components used in a solution
How are gel ophthalmics usually packaged?
In ophthalmic ointment tubes
What do ophthalmic suspensions usually contain?
A suspending, and sometimes dispersing agents
What size of drug particles are best for ophthalmic suspensions?
Submicron size range
Most suspending agents used in ophthalmic suspensions are ____ derivatives, ___ molecular weight polymers or _____
- Cellulose
- High
- Surfactants
Care must be taken w/ surfactants to avoid ..?
Irritation and disruption of the precorneal tear film
What do ophthalmic ointments contain?
Micronized drug dispersed in a petrolatum or other non-aqueous base
How are ophthalmic ointments packaged?
In lined metal tubes or plastic-foil laminated tubes
Which antimicrobial preservatives are effective against Pseudomonas species?
Benzalkonium chloride in combination w/ EDTA
What are advantages to benzalkonium chloride?
- Fast acting
- Good stability and wide spectrum of activity
- Stable over wide pH and temp ranges
What is the usual concentration of benzalkonium chloride? What should the concentration never exceed?
- Usual = 0.01%
- Never exceed 0.02% b/c will cause ocular discomfort
When is thimerosal used as an antimicrobial preservative?
When incompatibilities preclude the use of benzalkonium chloride
What is a disadvantage to thimerosal?
Slow acting and may cause sensitization and/or toxicity
What is the usual concentration of thimerosal for ophthalmics?
0.01%
Which parabens are used as ophthalmic preservatives and in what dosage form?
- Usually methyl and propyl esters used in combination
- Most often used in ointments
What is a disadvantage to parabens?
May cause burning sensation to eye
What are the usual concentrations of parabens used in ophthalmics?
- Methyl = 0.03-0.1%
- Propyl = 0.01-0.02%
What happens if a product is irritating to the eye?
Tearing will result and contact time will be reduced
What is the ideal buffer capacity for an ophthalmic product?
Adequate to maintain product, but low enough that when the product is instilled pH will rapidly adjust to 7.4
Generally, buffer concentration for ophthalmics should not exceed ____
100 mM
What is the function of viscosity increasing agents?
Increase contact time, reduce drainage rate, or enhance bioavailability
Which viscosity increasing agents are commonly used in ophthalmic products?
- Methylcellulose derivatives (hydroxypropylmethylcellulose, hydroxyethylcellulose, methylcellulose)
- Carbomers
- Polyvinyl alcohol
Why do you want an ophthalmic product to be isotonic?
To avoid ocular discomfort
What is the most common tonicity adjusting agent used in ophthalmic products?
Sodium chloride
When is sodium chloride not used as a tonicity adjuster and what would replace it?
- Glycerol or sugar
- Used when an ionizable tonicity adjuster will disrupt dispersive action of surfactants in the product
What is the most common antioxidant used in ophthalmic products?
Sodium bisulfite
Can pH be lowered in an ophthalmic product to prevent oxidation?
No b/c of the sensitive nature of eye tissues
What does surfactant selection depend on?
Potential to irritate the eye, damage cell membranes or disrupt precorneal tear film
Which surfactants are the only type suitable for ophthalmic products?
Non-ionic surfactants
What concentration of surfactant should be used for ophthalmic products?
As low as possible, but usually around 0.1%
What is the most common ointment base for ophthalmic products?
White petrolatum w/ mineral oil
____ drug particles must be used for ophthalmic ointments
Ultra-fine
How are ophthalmic ointments usually preserved?
- W/ parabens
- Products w/ broad spectrum antibiotics do not require antimicrobial agents if the product meets an appropriate microbial challenge test
For which products is the USP preservative effectiveness test not required for?
Products made w/ anhydrous non-aqueous vehicles
