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SoM 2 sim > Opthalmic Drug Administration > Flashcards

Opthalmic Drug Administration Flashcards

1
Q

Label the following diagram.

A
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2
Q

Describe the outer layer of the eye.

A
  • segment of two spheres: cornea and sclera
  • transparent cornea forward 1/6 of eye
    • in front of iris and pupil
    • innervated densely with sensory nerves
    • refracts and transmits light to lens and retina
    • protects against infection and damage
  • sclera 5/6, tough fibrous tissues
    • protects eye from internal and external forces (intraocular pressure of the eye)
    • maintains shape
    • dense connective tissue = white of eye
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3
Q

Describe the conjuctiva.

A
  • thin, transparent mucous membrane
  • covers visible part of eyelid - sclera
  • optic nerve emerges from sclera
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4
Q

What are the surfaces of the cornea and conjunctiva covered by?

A
  • film of tears produced by lacrimal gland
    • lubricates eye surface
    • protection from chemicals, microbes, airborne solid particles
  • 3 layers
  • mucuous layer
    • interacts with epithelial cells of cornea
    • each blink = spread of tear film
  • aqueous layer
    • electrolytes, proteins, glycoproteins, biopolymers, glucose, urea
  • superficial lipid layer
    • sterol esters, wax esters and fatty acids
  • dynamic equilbirium in pre corneal tear film (production, evaporation and drainage)
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5
Q

What are the three chambers of the eyes?

A
  • anterior
    • between cornea and iris
  • posterior
  • between iris and lens
  • vitreous cavity
    • 80% of eye
    • transparent, colourless and gelatinous mass
    • between lens and retina at back
    • 98% water - 2% collagen fibrils, hyaluronic acid, protein, inorganic salts, glucose

aqueous humour fills anterior and posterior chambers - clear, colourless and watery fluid

aqueous humour leaves anterior chamber via conventional and unconventional pathways

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6
Q

What happens if the aqueous humour cannot leave anterior chamber?

A

eg if exit blocked

fluid accumulates = increased pressure = glaucoma and damage to optic nerve

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7
Q

What are the main routes of ocular drug delivery?

A
  • cornea
    • topically administered drugs reach aqueous humour
  • blood retinal barrier (BRB)
    • restricts entry of drugs from systemic circulation into posterior segment of eye
    • retinal pigment eipthelium (RPE) - outer
      • solutes and nutrients from choroid to sub-retinal space
    • retinal capillary endothelium (RCE) - inner
      • junctions between cells mediate highly selective diffusion of molecules from blood to retina
      • retinal homeostasis
  • intravitreal delivery
    • inj into back of the eye (vitreous chamber)
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8
Q

What are the barried to ocular delivery?

A
  • aqueous humour into systemic uveoscleral cicrulation
  • aqueous humour outflow through trabecular meshwork and Schlemm’s canal
    • channel in eye that collects aqueous humour from anterior chamber and delivers into bloodstream via anterior ciliary veins
  • vitreous humour - diffusion into anterior chamber
  • posterior route across BRB
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9
Q

Discuss the osmolality of the eyes.

A
  • determine by conc of salt in lacrimal fluids
  • inorganic ions in tears: Na, K, Ca, Cl, HCO3- - control osmotic pressure of intra/extracellular fluids
  • healthy non dry eyes - 303mmol/kg at daytime
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10
Q

What is dry eye syndrome?

A

tear film hyper osmolality

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11
Q

What are the complications of hypotonic ophthalmic solutions?

A

corneal eipthelium more permeable = water flows into cornea = oedema

irritating to eye, increased production rate of tears

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12
Q

Describe the method of adjusting tonicity.

A
  1. identify reference solution and associated tonicity parameter
  2. determine contribution of drugs and additives to total tonicity
  3. determine amount of NaCl needed by subtracting contribution of actual solution from reference solution
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13
Q

Describe the pH of tears.

A
  • neutral
  • controlled by CO2, HCO3 and proteins, acidic tear prealbumin
  • buffer capacity is low but significant
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14
Q

What happens if an acidic or basic solution instilled in eye?

A
  • cannot be neutralised by tears
  • reflex tears generated to dilute the administered drop and eliminate it
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15
Q

What are the different types of tears?

A
  • basal tears
    • constant tears, protect cornea
  • emotional tears
  • reflex tears
    • irritation from foreign particles
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16
Q

Describe the ph of opthalmic formulations?

A
  • eye can tolerate topical formulation of pH 3.5-7
  • preferred: closest to 6.9-7.5
  • reduce discomport and associated increased lacrimation
  • important for drug ionisation (solubility/permeability) and product stability
17
Q

How can you maintain the pH of a opthalmic preparation at 4-5?

A

use of weak acidic buffer

eg acetic acid/ sodium acetete buffer or

citric acid/sodium citrate buffer

borate and phosphate buffers

18
Q

Why are viscosity enhancers used in opthalmic preparations?

A
  • prolong drug retention in pre-corneal tear film
  • enhance drug absorption
  • reduced drainage rate
  • thickness of precorneal tear film increased
  • drag water
  • stabilise aqueous layer as they spread over the corneal surface on blinking
  • increased volume act as a reservoir of drug
19
Q

What are examples of viscosity enhancing polymers used in opthalmic preparations?

A
  • water solublepolymers
  • poly(vinyl) alcohol
  • poly(vinylpyrrolidone)
  • cellulose derivatives
    • methylcellulose
    • hydroxypropyl methylcellulose
    • carboxymethyl cellulose (0.2-2.5%)
    • poly(ethylene) glycol 0.2-1%
20
Q

What is the surface tension of a healthy eye?

A

43.6-46.6 mN m-1

21
Q

What happens if a solution with lower surface tension of lacrimal fluid is adminstered to the eye?

A
  • destabilises tear film
  • disperses lipid layer into droplets that are solubilised by the drug or surfactant in formulation
  • in a healthy eye, oily film reduces rate of evapoation of underlying aqeuous layer
    • once lost, dry spots formed = painful and irritant
22
Q

What is the role of surfactants in opthalmic preparations?

A

solubilise or disperse drugs

23
Q

What is the best type of surfactant to use in opthalmic preparations?

A

non-ionic

cationic binds to cell surface membrane (-) = toxic

eg polysorbate 20, polyoxyl 40 stearate

24
Q

What are the downsides of using a non-ionic surfactant in opthalmic formulations?

A
  • remove mucus layer
  • disrupt tight junctional complexes of cornea
  • interact with polymeric substances (viscosity enchancers) in the preparation
  • reduce the efficacy of preservatives

conc of surfctant important

  • drug solubility
  • safety and patient tolerance
  • high conc = foaming upon manufacturing and shaking
25
Q

What are sterility requirements of opthalmic preparations?

A
  • must be sterile at time of filling and closing in sealed container
  • terminal sterilisation preferred
  • if filtration: pore size is 0.22mcm
  • raw materials should be sterile, whenever possible or should meet low bioburden control limit
  • containers must be labelled with duration of use once opened
26
Q

What are requirements of preservatives in opthalmic preparations?

A
  • included in multi dose containers
  • destroy and inhibit microorganisms growth
  • not to be used for intraocular administration = causes irritation
  • broad spectrum anti-microbial activity (against gram +/- bacteria)
  • exhibit compatability and stability with all ingredients
  • harmless to ocular tissue
27
Q

What are examples of preservatives used in opthalmic preparations?

A
  • benzalkonium chloride
    • 0.004-0.02%
    • quaternary ammonium salt
    • repeated admin. = epithelial toxicity
  • phenylmercuric nitrate
    • organomercury compound
    • powerful antiseptic and antifungal
    • low conc

no preservatives in single dose units

28
Q

What are labelling requirements of opthalmic preparations for hospital use?

A
  1. volume of contents - should not exceed 10mL
  2. official name of preparation
  3. conc of API (%w/v)
  4. name and conc of preservatives
  5. directions
  6. “sterile until opened”
  7. “to be used for one eye of one patient only” if patient named, what eye?
  8. “use with care to avoid contamination during use”
  9. “to be discarded _ after first opening” (one week for hospital, at end of day for outpatient department use)
  10. storage requirement
  11. expiry date
  12. batch and product license number
  13. POM or P
  14. name of patient (hospital ward)
  15. date of issue
  16. “for external use only”
  17. “keep out of reach of children”
  18. name and address of supplier
29
Q

What are labelling requirements of opthalmic preparations for hospital use?

A
  1. official name of preparation
  2. conc of API when monograph allows variable conc
  3. directions
  4. “sterile until opened”
  5. “use with care to avoid contamination during use”
  6. “to be discarded one month after first opening container”
  7. storage requirements
  8. name of patient
  9. date of dispensing
  10. “keep out of reach of children”
  11. “for external use only”
  12. name and address of supplier
30
Q

Describe the eye drop containers used.

A
  • glass bottles
    • amber coloured, vertically ribbed
    • neutral glass or soda glass
    • fitted with phenolic plastic screw cap (neutral glass dropper tube fitted with natural or synthetic rubber teat)
    • or complete dropper clsure may be sterilised - supplied separately
  • suitable plastic containers
31
Q

Describe the limitations to the use of rubber teats for opthalmic prep.

A
  • may be incompatabile with benzoalkonium chloride
  • storage limited to 3 months
  • slightly permeable to water vapour
  • gradual loss of water for prep occurs
  • complete dropper assembly should be supplied seperately
    • before issue for use, dropper asssembly should be echanged with plain phenolid cap with silicone rubber linear
  • readily breakable seals
32
Q

How do you consel patients on eye drops?

A
  • if 2 eye drops, wait 5-10 between
  • eye drops before ointment
  • wash hands before
  • keep in a cool dry place away from heat
  • dont let tip touch eye
  • close eyes after administration

SoM 2 sim (21 decks)

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