Choices of local anaesthetic

Lidocaine and bupivacaine are both amide local anaesthetics, but they differ substantially in onset, potency, duration, tissue distribution, and toxicity profile. This Pain Update will help you choose which one to select for canine and feline local anaesthesia. We've considered lidocaine and bupivacaine as the main locals available in veterinary practice.

Read Basics of Local Anaesthetics

The simple why –

Less pain: local anaesthetics enable us to reduce opioid consumption in the post-op period.

Reduced adverse effects: local anaesthetics allow a dose reduction in opioids and volatile agents, both of which have adverse effects. The adverse effects profile of local anaesthetics is favourable.

Cost: local anaesthetics are cheap analgesics. They also bring further cost savings in reduced opioid consumption in the post op period.

Property	Lidocaine	Bupivacaine
Class	Amide local anaesthetic	Amide local anaesthetic
pKa	~7.8	~8.1
Lipid solubility	Moderate	High
Protein binding	~65%	~95%
Onset	Rapid	Intermediate/slower
Duration (soft tissue infiltration)	1–2 h	4–8 h or longer
Sensory vs motor block	Similar sensory and motor effects	More sensory-selective at lower concentrations – although difficult to document in dogs and cats
Cardiotoxicity	Lower	Significantly higher
Typical clinical use	Short/intermediate procedures, IV lidocaine infusions, antiarrhythmic	Long-lasting regional techniques and postoperative analgesia

Pharmacology

Lidocaine

• Lower pKa means a greater fraction is non-ionized at physiological pH.

• Crosses nerve membranes relatively quickly.

• Produces a rapid onset block, often within minutes.

• Moderate lipid solubility results in a shorter duration compared with bupivacaine.

  
  

Bupivacaine

• More lipid soluble and highly protein bound.

• Binds more strongly to sodium channels.

• Slower onset but substantially longer duration.

• Greater differential block, allowing sensory blockade to outlast motor blockade in some techniques.

  
  

Clinical Effects

Onset

Lidocaine generally works faster.

For example:

• Peripheral nerve block: lidocaine may start working in 5–10 minutes.

• Bupivacaine may require 15–30 minutes depending on the nerve and concentration.

  
  

This difference is often attributed to lidocaine's lower pKa, although concentration and dose also play major roles. However, this does depend on the size of the nerve and we do see a difference between dental nerves and a larger nerve such as the sciatic. Clinically, we do not see such a slow onset of action with bupivacaine for those smaller dental nerves. In a clinical audit, we did note a more rapid onset of action when lidocaine and bupivacaine were combined in a 50:50 ratio.

We explore the question of combining locals here

Duration

Bupivacaine lasts much longer.

Approximate durations:

This prolonged action makes bupivacaine preferable when prolonged postoperative analgesia is desired.

Toxicity

LAST – local anaesthetic systemic toxicity

CNS Toxicity

These effects are reported in people, however difficult to document all of these in our patients:

• Tinnitus

• Circumoral numbness

• Muscle twitching

• Seizures

• CNS depression at higher doses

Cardiovascular Toxicity

This is where the major difference lies.

Bupivacaine:

• High affinity for myocardial sodium channels.

• Slow dissociation from channels during diastole.

• More likely to cause severe ventricular arrhythmias and cardiovascular collapse.

• Resuscitation may be difficult following inadvertent intravascular injection.

Lidocaine:

• Considerably safer from a cardiac perspective.

• Ventricular arrhythmias can occur in overdose but are generally easier to manage.

A useful teaching point is:

"All local anaesthetics can cause LAST, but bupivacaine is the one we fear most."

The golden rule is to always aspirate prior to injection, and aspirate every time you move your needle.

Veterinary Considerations

In veterinary anaesthesia:

Lidocaine

Commonly used for:

• Line blocks and infiltration

• Intravenous analgesic infusions

• Antiarrhythmic therapy for ventricular arrhythmias in dogs

Bupivacaine

Commonly used for:

• Peripheral nerve blocks

• Dental blocks

• TAP blocks

• Epidurals requiring long postoperative analgesia

• Wound-soaker catheters and locoregional analgesia

Many veterinary anaesthetists will choose:

• Lidocaine when rapid onset is important.

• Bupivacaine when prolonged analgesia is the primary goal.

Concentration matters

The higher the concentration (ie: bupivacaine 0.5% or 0.25%) the better the block

Practical Summary

Lidocaine

• Faster onset

• Shorter duration

• Less cardiotoxic

Bupivacaine

• Slower onset

• Much longer duration

• More potent and highly protein bound

• Significantly greater cardiotoxic potential

• Preferred for long-lasting regional analgesia

Final thought

In daily practice I always opt for bupivacaine where possible, due to the longer effect.

This post was written by Matt Gurney.

Matt & Carl established Zero Pain Philosophy to provide educational resources & telemedicine to veterinary professionals globally, enabling optimal management of pain.

Matt Gurney is an RCVS & European Specialist in Veterinary Anaesthesia & Analgesia and works at VES Hospital in Singapore. Matt is Past President of the European College of Veterinary Anaesthesia & Analgesia.

Carl Bradbrook is an RCVS & European Specialist in Veterinary Anaesthesia & Analgesia and is Past President of the Association of Veterinary Anaesthetists. Carl works for Mars Vet Health in Singapore.