15.2 Local anesthesia (TSDHT)

Local anaesthetics (LAs) vary in potency, toxicity, duration of action, stability, water solubility and ability to penetrate mucous membranes. These determine the route of administration.

After most regional LAs maximum arterial plasma concentrations develop within 10-20 minutes, so monitoring of toxic events should take place during the first 30 minutes after injection. Care should be taken to avoid accidental intravascular injection.

LA toxicity usually results from excessively high plasma concentrations. Effects initially include light-headedness, sedation, parasthesia and twitching. Convulsions can occur in severe reactions. With inadvertent IV injection convulsions and serious cardiac events may occur rapidly particularly with bupivacaine.

Most LAs cause vasodilation and adrenaline (1:200000) may be added which promotes vasoconstriction and prolongs the local activity of the LA. LA with adrenaline combinations should not be used on digits and appendages.

Lidocaine hydrochloride
  • Injection 20mg in 2ml (1%) (£0.96 = 1 ampoule)
  • Injection 50mg in 5ml (1%) (£0.44 = 1 ampoule)
  • Injection 100mg in 5ml (2%) (£0.27 = 1 ampoule)
  • Injection 50mg in 10ml (0.5%) (£0.67 = 1 ampoule)
Lidocaine with adrenaline
  • Injection 10mg/ml (1%) with adrenaline 5 micrograms (1 in 200,000) (£1.93 = 20ml ampoule)
  • Dental cartridge 44mg/2.2ml (2%) with adrenaline 27.5 micrograms/2.2ml (1 in 80,000) (£0.47 = 1 cartridge)
  • Injection 200mg (1%) with adrenaline 100 micrograms (1 in 200,000) in 20mL vial preserved
  • Injection 400mg (2%) with adrenaline 100 micrograms (1 in 200,000) in 20mL vial preserved
Lidocaine 10%
  • Spray (£6.29 = 50ml bottle)
Lidocaine 5%
  • Ointment (£6.18 = 15g)
Tetracaine
  • 4% gel 1.5g (£1.08)

Notes

  1. Tetracaine gel is indicated prior to venepuncture. After application (together with an occlusive dressing) venepuncture may be carried out after 30 minutes, with anaesthesia lasting 4-6 hours. It is rapidly absorbed from mucous membranes and should never be applied to inflamed, traumatised or highly vascular surfaces. It is not recommended for infants under 1 month or for premature infants.
  2. Tetracaine gel is preferred to Emla® because it is quicker acting and can be used on infants under 1 year (but over 1 month).
Emla® Cream
  • Lidocaine 2.5%, prilocaine 2.5%, 30g, 5g (£2.25 = 5g)

Notes

  1. Lidocaine and prilocaine cream (Emla®) has been added for use in patients unable to tolerate tetracaine.
Lidocaine 700mg (5% w/w)
  • Ralvo® medicated plaster (£61.54 = 30)

Indications

  • Post-herpetic neuralgia only (see Management of neuropathic pain) (but see notes below)
  • Not to be used for non-neuropathic pain e.g. fibromyalgia, musculoskeletal pain, headache etc.

Dose

  • Apply once daily for up to 12 hours, followed by a 12-hour plaster-free period; discontinue if no response after 4 weeks; up to 3 plasters may be used to cover large areas; plasters may be cut.

Notes

  1. Following national guidance from NHS England, not recommended for initiation in primary care. Click here for more information
  2. Only indicated for the treatment of post-herpetic neuralgia, following initiation by specialist pain team
  3. Lidocaine plasters are only licensed for use in post herpetic neuralgia; there is a paucity of data from double blind RCTs demonstrating efficacy in other neuropathic conditions. Pain specialists may occasionally recommend a trial of lidocaine plasters in difficult to treat cases of other forms of neuropathic pain. If successful, GPs may be asked to continue prescribing with ongoing review from pain specialists
  4. Lidocaine plasters can result in gradual desensitisation of the nerves, leading to improvement in symptoms; the plaster may be discontinued if this should occur. Prescribers should therefore consider a trial withdrawal of therapy to reassess ongoing need at appropriate intervals
Lidocaine 4% topical solution
  • 30ml (unlicensed)

Bupivacaine is the principle LA for spinal anaesthesia. It is often used in lumbar epidural blockade and is particularly suitable for continuous epidural analgesia in labour. It has a longer duration of action compared to other LAs.

Bupivacaine hydrochloride
  • 0.125% in 65mL, 250ml
  • 0.5% in 4ml (Marcaine® heavy)
Bupivacaine with adrenaline
  • Injection 25mg (0.5%) with adrenaline 50 micrograms (1 in 200,000) in 10ml ampoule
  • Injection 50mg (0.5%) with adrenaline 50 micrograms (1 in 200,000) in 10ml ampoule
Cocaine 10% CD
  • Spray
Cocaine 5% with adrenaline 1 in 2000 CD
  • Gel

Notes

  1. Cocaine solution is used for topical anaesthesia of the nose and Cocaine with adrenaline gel is used for topical anaesthesia for minor cuts. Both are pharmaceutical specials.
Levobupivacaine
  • Injection 2.5mg/ml (0.25%), 10ml ampoule
  • Infusion 2.5mg/ml (0.25%), 250ml
  • Injection 5mg/ml (0.5%), 10ml ampoule
  • Infusion 0.125%, 250ml
Levobupivacaine with fentanyl
  • 0.1% with 2 micrograms/ml fentanyl in 250ml
Mepivacaine hydrochloride
  • Injection 30mg/ml (3%) 2.2ml cartridge (for podiatry)
Prilocaine
  • Injection 50mg (0.5%) 50ml ampoule
  • Injection 20mg/ml
  • Injection 60mg with felypressin 1.04mg cartridge (for dental anaesthesia)

Notes

  1. Prilocaine is associated with low toxicity and is the agent of choice for IV regional anaesthesia (e.g. Bier's block).

 

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