anaesthetics

• Anaesthesia

  Induces insensitivity to pain
• Analgesics

  Usually provide a more general vs. a localised effect
• Topical

  To be applied to a surface in the body (e.g. skin or mucous membranes, including those of the eye)
• Local

  To have a localized effect, best achieved by injection
• General

  Inhaled or injected anaesthetics administered by an anaesthetist as part of preparation for major surgery
• Topical (when used in BNF) means skin
• Eye (when used in BNF) means eye
• Mechanism of local anaesthetics

  1. Nerves serving the senses are affected first (pain)

  2. Next affected are nerves transmitting touch and temperature

  3. Pressure is affected last

  4. Local anaesthetics work by reversibly blocking transmission along sensory nerves

  5. By blocking sodium channels involved in pain impulse transmission
• Mechanism of topical ocular local anaesthetics

  1. Usually produce anaesthesia within 1 minute

  2. Anaesthesia lasts 15-30mins
• Classes of local topical ocular anaesthetics

  • Esters
  • Amides
• Ester class

  • Oxybuprocaine
  • Tetracaine
  • Proxymetacaine
• Allergies seem to be class specific
• General information about local topical ocular anaesthetics

  • PoM, use only
  • Low concentrations (0.1, 0.125%) sufficient to carry out optometric procedures
  • Concentrations used in products (0.4, 0.5%) are excessive - anaesthesia deeper than needed
  • Recovery proportional to concentration
  • Vehicle and preservative have minimal effect on performance of local anaesthetic
• Order of stinging on installation (least to most)

  • Proxymetacaine
  • Oxybuprocaine
  • Lidocaine
  • Tetracaine
• Proxymetacaine

  • Proparacaine in USA - same product but different name
  • White/off white powder
  • Soluble in water 1:30
  • Synthetic - something made
  • Ester
• Timing of proxymetacaine

  1. 1 drop 0.5% = lasts 15min

  2. Onset 6-20secs (average 13sec)
• Proxymetacaine products (BNF)

  • Minims proxymetacaine 0.5% eye drops
  • 0.5ml unit dose
  • PoM
  • Active ingredients: Proxymetacaine hydrochloride 5 mg per 1 ml unit dose
  • 20 in a box
  • NHS indicative price £12.12
• Proxymetacaine (BNF; Optometrist's formulary)

  • Indications: local anaesthetic
  • Dose: For adult and children (1month and over) apply as required; 1-2 drops sufficient
  • Contra-indications: Hypersensitivity to proxymetacaine or other ester-type anaesthetics, Avoid in preterm neonates
  • Cautions: Use cautiously and sparingly in patients with known allergy, cardiac disease, hyperthyroidism
  • Protect the eye from foreign bodies and rubbing during the period of anaesthesia (up to 30 minutes)
  • Ideally the patient should not leave the practice until corneal sensation has returned
  • Pregnancy and lactation: No well-controlled clinical trials, do not use unless considered essential
  • Ocular side effects: transient stinging, transient blurring, punctate keratitis, conjunctival hyperaemia, pupillary dilatation or cycloplegic effects rarely
  • General side effects: none reported
• Proxymetacaine storage

  • Kept somewhere dark
  • Once opened 2-8deg (i.e. keep refrigerated)
  • If kept at room temperature: Store at <25deg for up to 1month
• Proxymetacaine properties

  • Least stingy
  • Less intrinsic antibacterial action than other topical anaesthetics
  • Useful for use in patients before taking swabs
• Oxybuprocaine

  • White crystals or white powder
  • Very soluble in water
  • Synthetic
  • Ester
  • Once known as benoxinate
• Timing of oxybuprocaine

  1. Superficial FB or tonometry: 1 drop, produces anaesthesia in 60s, lasts 10-15min

  2. Remove corneal FB or inclusion of a meibomian cyst: 3 drops over 4-5mins, do procedure after a further wait of 5mins, sensitivity normal in about 1hour after 3 drops
• Oxybuprocaine products (BNF; Optometrists Formulary)

  • Minims oxybuprocaine hydrochloride 0.4% eye drops
  • 0.5ml unit dose
  • PoM
  • Active ingredients: oxybuprocaine hydrochloride 4 mg per 1 ml unit dose
  • 20 in a box
  • NHS indicative price £10.56
• Oxybuprocaine (BNF; Optometrists Formulary)

  • Indications: local anaesthetic
  • Dose: For adult and children >1month apply as required
  • Contra-indications: Hypersensitivity to oxybuprocaine or other ester-type anaesthetics, Avoid in preterm neonates
  • Cautions: Eye should be protected from foreign bodies and rubbing during the period of anaesthesia (up to 30 minutes), Ideally the patient should not leave the practice until corneal sensation has returned
  • Pregnancy and lactation: No well-controlled clinical trials, should not be used unless considered essential
  • Ocular side effects: transient stinging, transient blurring, punctate keratitis, Hypersensitivity reactions may occur rarely: allergic conjunctivitis, peri-orbital oedema
  • General side effects: None reported
• Oxybuprocaine storage

  • Store <25deg (does not need refrigeration)
  • Keep in a dark place (if degrades, can change to a pale brown colour)
• Oxybuprocaine properties

  • Less irritation and stinging than tetracaine but more than proxymetacaine
  • Bactericidal properties
• Tetracaine

  • White crystalline powder
  • Soluble in 1 in 7.5 water
  • Ester
  • Once known as amethocaine
• Timing of tetracaine

  1. Initial stinging that goes away in <30s

  2. Little clinical difference in effect to proxymetacaine, similar duration

  3. Superficial FB/tonometry: 1 drop, onset 9-26secs (ave 15sec), lasts 10-20min
• Tetracaine products (BNF; Optometrists formulary)

  • Minims tetracaine hydrochloride 0.5% eye drops, 0.5ml unit dose, PoM, Active ingredients: tetracaine hydrochloride 5 mg per 1 ml unit dose, 20 in a box, NHS indicative price £10.57
  • Minims tetracaine hydrochloride 1% eye drops, 0.5ml unit dose, PoM, Active ingredients: tetracaine hydrochloride 10 mg per 1 ml unit dose, 20 in a box, NHS indicative price £10.57
• Tetracaine (BNF; Optometrists formulary)

  • Indications: local anaesthetic
  • Dose: For adult apply as required
  • Unlicensed use: In children. Not licensed for use in neonates
  • Contra-indications: Avoid in preterm neonates
  • Contraindications/Interactions: Sulphonamides (should not be used in patients taking these)
  • Cautions: Eye should be protected from foreign bodies and rubbing during the period of anaesthesia (up to 30 minutes), Ideally the patient should not leave the practice until corneal sensation has returned
  • Pregnancy and lactation: No well-controlled clinical trials, should not be used unless considered essential
  • Side effects: transient stinging, transient blurring, punctate keratitis, conjunctival hyperaemia, A severe, immediate-type, apparently hyperallergic corneal reaction may occur (rare)
  • General side effects: None reported, Systemic toxicity mainly involves CNS, Systemic effects unlikely with topical application
  • Hypersensitivity and cross-sensitivity: Hypersensitivity reactions occur mainly with the ester-types, less common with amides types. Reactions may be avoided by using the alternative chemical type
  • Breast feeding: With topical use, not known to be harmful
• Tetracaine storage

  • Store below 25deg
  • Store in dark place
• Tetracaine properties

  • Most stingy topical ocular anaesthetic
• Lidocaine

  • White crystalline powder
  • Soluble in <1 part water
  • Amide
• Limited published information on timing of lidocaine
• Conjunctival hyperaemia


  A severe, immediate-type, apparently hyperallergic corneal reaction
• Severe, immediate-type, apparently hyperallergic corneal reaction

  1. Acute, intense and diffuse epithelial keratitis

  2. Grey ground-glass appearance

  3. Sloughing of large areas of necrotic epithelium
• No general side effects reported
• Systemic toxicity mainly involves CNS
• Systemic effects unlikely with topical application
• Hypersensitivity and cross-sensitivity

  Hypersensitivity reactions occur mainly with the ester-types, less common with amides types. Reactions may be avoided by using the alternative chemical type.