CH 17 -- Special Solutions (pt 1) Flashcards
drugs are applied to the eye for….
the LOCALIZED effect of the medication on either the surface of the eye or its interior
name the dosage forms of opthalmic drug delivery
-aqueous solutions
-suspensions
-ointments
-inserts
what is the first choice of dosage form for the eyes?
aqueous solutions (aka drops)
for a medicine dropper, 1mL = __drops
20 drops
what are SIX disadvantages of ophthalmic solutions
-loss of instilled medication
-removal by the naso-lacrimal system
-short retention time on the eye surface
-frequent administration
-therefore: patient inconvenience and noncompliance
-low bioavailability
1 disadvantage of ophthalamic solutions:
“loss of medication using regular eye droppers”
Explain this.
for a regular eye dropper, 1mL = 20drops.
therefore, 1 drop=50 microliters
our blinking eyes can only hold 10 microliters. Therefore, 40 microliters are being wasted. This is an 80% loss
our normal tear volume is ___ microliters.
if not, you have ___ syndrome
7 microliters
dry eye syndrome
eyes that are NOT blinking can hold up to ___ microliters.
but when blinked, it can only retain ___ microliters
non blinking eye can hold up to 30 microliters
but when blinked, it can only retain about 10 microliters
our tears are produced where?
the lacrimal gland
a problem with ophthalmic solutions:
Removal by the naso-lacrimal system.
explain this further
when reflex tearing causes volume greater than 7-10 microliters, the drug undergoes superficial adsorption through the conjunctiva. this causes a rapid removal by peripheral blood vessels and eventually goes to the GI tract.
this causes a potential SYSTEMIC EFFECT. we don;t want this. the purpose of ophthalmic delivery is for local effects either on the surface or interior of the eye. this can cause side effect
what is a method to avoid systemic absorption of the active ingredient(s) that results from the drainage of the drug through the nasolacrimal duct and then swallowed?
by applying gentle pressure to the lacrimal sac for 3-5mins after administration
why is there such a short retention time of ophthalmic solutions on the eye?
because the eye surface is very small, and we blink and cry when something is applied to the eye.
due to this, eyedrops require frequent administration which is another disadvantage
ophthalmic solutions have low bioavailability. give an example and explain why this isn’t a huge problem and therapeutic effects can still exist
pilocarpine ophthalmic solution has <1% bioavailability
however, therapeutic effects still exist because we only want local effects. the drops are being applied right at the receptor site
name 2 methods to enhance bioavailability of ophthalmic solutions
greater drug concentration (most ophthalamic solutions have a HIGH concentration)
OR
increase corneal contact time (5 diff dosage forms) one example: mucoadhesive polymers, adsorbable gelatin sponge
how do you calculate the effective “dose” of ophthalmic solution actually applied?
-strength of dose administered
-volume administered
-retention time of the drug on the surface of the eye
-frequency of administration
when considering the “volume administered” in calculating the effective dose of an ophthalmic solution, what should you keep in mind?
each drop is 50 microliters BUT the eye can only hold 10microliters. 40 microliter loss (80%)
name 7 pharmaceutical requirements in the preparing of solutions and suspensions for ophthalmic use
-sterility and preservation
-isotonicity value
-buffering
-viscosity and thickening agents
-OCULAR bioavailabiliy
-additional considerations
-packaging
which 2 dosage forms MUST be sterile
parenteral and ophthalmic
the greater the retention time, the ___ the absorption
better
name 2 methods for sterilization
autoclaving and membrane filtration
WHY is preservation needed for ophthalmic products?
the packaging is “multiple dose” meaning that the patient will be using it many times after it has been opened
syrup preservative is mainly used against ____ while ophthalmic preservative is mainly to combat ____
syrup – mainly fungi
ophthalmic – mainly bacteria
paraben group preservatives are against ___ and NOT ___
against FUNGI and NOT bacteria
for preservative for ophthalamic solutions, when would you want to use the ionized form of a preservative and when would you want to use the unionized form?
ionized — longer duration
unionized – more effective (can cross cell membrane)
name all 6 preservatives for ophthalmic products and whether they are ionized or unionized
benzalkonium chloride – ionized
benzethonium chloride – ionized
chlorobutanol – unionized
phenylmercuric acetate - unionized
phenylmercuric nitrite – unionized
thimerosal – ionized
what is the name of the bacteria that CANNOT be in the eyes or it will cause loss of vision and is not destroyed by the aforementioned 6 preservatives
Pseudomonas aeruginosa
are parabens used as a preservative in ophthalmic preparations? explain
NO. paraben groups are for FUNGI and not bacteria
isotonicity related to ophthalmic preparations is important to ensure ____
comfort when the solution/suspension is applied to the eye
name 2 osmolarity-adjusting agents
NaCl (0.7-1.5%)
mannitol
which does the eye tolerate better — hypotonic solutions are hypertonic solutions
hypertonic. this is so because the discomfort is only TEMPORARY – our tears will dilute the hypertonic solution which will bring it lower.
body fluids, INCLUDING BLOOD AND TEARS, have an osmotic pressure corresponding to that of a ___% solution of sodium chloride
0.9%
when are eye solutions said to be isotonic
when OUR osmotic pressure is the same as the SOLUTION APPLIED
when the particles are UNCHARGED (as with sucrose), osmotic pressure depends solely on….
the number of molecules present
When the particle is an ELECTROLYTE (as in sodium chloride), the number of particles that it contributes to the solution will depend on…..
the concentration of the molecules present and ALSO the degree of ionization
