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13 Cards in this Set
- Front
- Back
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Commonly used LAs
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Oxybuprocaine hydrochloride 0.4%
Proxymetacaine hydrochloride 0.5% Amethocaine 0.5/1% Lignocaine (4%) + fluorescein (0.25%) |
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LA mechanism of action
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Prevent nerve impulse conduction/generation
Affect pain nerves first - smallest nerves Act @ cell membrane to prevent action potentials Reversible |
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LA types
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Synthetic - cocaine
Esters - all others; plasma metabolism Amides - lignocaine; liver metabolism |
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LA chemistry
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Contact w/ more alkaline solution --> non-ionised/lipid soluble form released
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Max effective conc.
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Conc beyond which no further activity increase occurs
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Proxymetacaine
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Most comfortable - toxic effects very rare
Less intrinsic antibacterial action --> scraping use |
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Oxybuprocaine
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Most intrinsic antibacterial action --> no scraping use
Very safe - toxic effects very rare |
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Amethocaine
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Least comfortable/significant irritation
Affected by light |
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Lignocaine
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Contact tonometry use w/ fluorescein
Amide - alternative in ester allergy |
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LA desquamation
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Epithelial cell loss/sloughing
Greater in older Px/dry eyes Measured via cell irrigation |
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LA hypersensitivity reactions
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Local reaction - conjunctival hyperaemia/chemosis, lid oedema, lacrimation
5 - 10 mins post instillation Tx - anti-histamine, cold packs + topical decongestant Delayed reaction possible - 6 to 12 hrs later |
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LA toxic overuse
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Epithelium loss + inhibited epithelial defect healing
Tear film instability + decreased blink rate w/ hypoaesthesia Chronic non-healing epithelial defect --> corneal scarring Tx - LA cessation, atropine, pressure patching + antibiotics |
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LA precautions
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Poor epithelial integrity
CL wear - wait 30 mins before wearing Amethocaine avoided in Px treated with sulphonamides High doses w/ pupil dilation/cycloplegia Pregnancy + lactation - safe to use |
