Wk 13 - Ocular Anesthetics Flashcards
Ester-linked Local Anesthetics
Most topical anesthetics.
Locally metabolized by esterase enzymes:
• Shorter duration of action
Categories: 1) PABA • Tetracaine • Benoxinate 2) MABA • Proparacaine 3) Cocaine
Amide-linked Local Anesthetics
Most injectable anesthetics
Metabolized only in the liver:
• Longer duration of action
Examples:
Lidocaine
Ocular Anesthetic MOA
Sodium channel blockers / Inhibit nocireceptor signal transduction
1. Non-ionized, lipid soluble drug crosses membrane of sensory neuron axon
2. Drug is ionized inside cell
3. Drug blocks Na+ channels to prevent Na+ influx
4. Neuron is unable to depolarize and send sensory signal
5*. If ester-linked, local cellular enzymes break down the drug over time
Ocular Anesthetic Duration of Action
Duration of action is proportional to the time length of drug contact with nerve.
Contact time is affected by:
1) Drug structure
• Amide-linked removed less quickly than ester-linked
2) Concentration of solution
• Higher concentration has longer contact time
3) Rate of removal from site
• Slower rate of removal has longer contact time
Cocaine
Topical Anesthetic
-Prototype anesthetic drug, but not commercially available due to potential for abuse (schedule II drug)
o Must be compounded at a pharmacy
Cornea effects o Onset: 2% sol produces anesthesia in 5-10 min o Duration • Complete anesthesia for 20 min • Incomplete anesthesia for 1-2 hours Conjunctiva effects o Duration: 15-20 min o Includes vasoconstriction due to sympathomimetic effects
MOA
1) Blocks neuronal reuptake of norepinephrine to prolong sympathetic effects
- > Mydriasis and vasoconstriction
2) Blocks neuronal Na+ channels
- > Anesthesia
Adverse effects of topical Cocaine
1) Corneal damage
• Loosened epithelium
• Grey corneal pitting and irregularities
2) Systemic absorption via mucous membranes
• CNS stimulation
• Elevation of blood pressure
• Avoid in HTN patients
Clinical uses of topical Cocaine
1) Debridement of corneal ulcers
• Produces anesthesia and loosens epithelium so that it is easier to remove
2) Diagnosis of Horner’s syndrome
• Fails to dilate the pupil if disease is present
Pontocaine (0.5% tetracaine sol)
Onset: 10-20 sec
Duration: 10-20 min
Less comfortable than benoxinate or proparacaine
Side effects
• SPEE/SPK
• Rare allergic reactions
Contraindication: topical sulfonamide therapy
• Interferes with sulfa drug action
TetraVisc Forte (high viscosity 0.5% tetracaine sol)
Preparations
• Multi-dose 5 mL bottle
• Unit dose 0.6 mL bottles
Efficacy: similar to Akten (lidocaine 3.5%)
Higher viscosity than standard tetracaine sol
• Increased contact time
Clinical use
• Apply to conjunctival or lid for surgical procedures
• Improves pain levels in post-op patients
Benoxinate: Fluress (0.4% benoxinate + 0.25% NaFl)
Benoxinate is only commercially available topically with NaFl
• Bactericidal properties prevent bacterial growth in NaFl sol
Onset, duration, and intensity equal to tetracaine
Clinical use: Goldmann tonometry
Side Effects
• SPEE with epithelial desquamation
• Rare allergic reaction
Proparacaine 0.5% sol (Alcaine, Ophthaine, Ophthetic)
Most comfortable of the topical ocular anesthetics
Clinical use: General ophthalmic anesthesia
Onset, duration, and intensity similar to tetracaine
Side effects (rare) • Mild stromal edema • SPEE and epithelial stippling • Conjunctival hyperemia and chemosis • Lid edema
Fluorocaine (0.5% proparacaine + 0.25% NaFl sol)
Clinical use: Goldmann tonometry
o Less commonly used than Fluress
Akten (PF 3.5% lidocaine gel drop)
Increased duration of effect
• Viscous gel formula
• Amide-linked
Clinical use: Ocular surface anesthesia during ophthalmologic procedures
Apply 2 drops to ocular surface in area of planned procedure
o Onset: 20-60 sec
o Duration 5-30 min
Lidoderm (5% lidocaine patch)
Apply to intact skin for treatment of post-herpetic neuralgia
EMLA cream or patch (2.5% lidocaine and 2.5% prilocaine)
o Treats post-herpetic neuralgia
o Pre-op treatment for removing benign skin lesions
Choosing a topical ophthalmic anesthetic
All have similar
o Onset (15-30 sec)
o Duration of maximum effect (15-20 min)
o Duration of incomplete effect (45-60 min)
• So choose the drop that is most comfortable and has the fewest side effects for your patient
• If patient has a hypersensitivity reaction to one drug, switch to a different class
-Ex. Patient reacts to tetracaine, which is a PABA drug, switch to proparacaine, since it is MABA
Topical Anesthetic Adverse Effects
Topical drops have fewer side effects than injectable anesthetics but are More likely to have local side effects than systemic
1) Local irritation
o Mild burning and redness that quickly resolve
• Rare hypersensitivity
• Systemic effects
2) Nervousness, tremors, convulsions, depressed CNS (reduced breathing, loss of consciousness)
o No reported cases of serious systemic reactions to a topical anesthetic
3) Induced corneal syndrome
o Occurs within 6 days to 6 weeks of prolonged topical anesthetic use
• Never Rx a patient a topical anesthetic or allow a patient to self-administer one
o Usually patients with medical, paramedical, or welding backgrounds
o Drugs inhibit healing of cornea and produce loss of epithelium
o Corneal stromal ring
• DDx: acanthamoeba
o Conj hyperemia
o Treatment
• Discontinue anesthetic use
• 1% atropine bid for pain
• Apply pressure patch with analgesic and prophylactic antibiotic if epithelial damage warrants
Topical Anesthetic Precautions
o Limit dosage and concentration of drug and frequency of use
o Administer to seated or recumbent patient in case of fainting
o Depress puncta and use sparingly with conjunctival hyperemia to limit systemic absorption
o Increase duration of effect by using soaked cotton swab or pledget for greater contact time
Use of Topical Anesthetic for RGP Fitting
Studies show that using a topical anesthetic while fitting an RGP
o Does not cause more epithelial damage than saline
o Reduces time needed to obtain and analyze NaFl pattern
o Allows for more patient comfort
Injectable Anesthetics
Lidocaine
Indications • Tissue infiltration o Benign lid lesion excision o Chalazion excision o Laser photocoagulation to treat trichiasis o Argon laser punctoplasty • Facial nerve block • Retrobulbar nerve block
Added epinephrine
• Causes vasoconstriction to:
o Prolong duration of anesthesia
o Decrease systemic absorption
o Decrease bleeding
• Concentration: 1:50,000 to 1:200,000
o 1:100,000 is most common
• Avoid use in nerve blocks due to side effects
• Avoid contact with fingers/nose due to vasoconstriction
• Side effects: tachycardia, hypertension, headaches
Lidocaine (Xylocaine)
Be most familiar with this local injectable
• Onset: 4-6 min
• Duration: 40-60 min, 120 with epinephrine
