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Pharmacology Reference

Local Anaesthetic Drugs

Comprehensive reference for local anaesthetic agents used in emergency medicine regional blocks. All doses are maximum total doses — individual block volumes must be calculated based on patient weight. Always use the lowest effective dose and concentration.

Quick Comparison

DrugClassMax Dose (plain)OnsetDurationCardiotoxicity
Lidocaine (Lignocaine)Amide3 mg/kg (without adrenaline); 7 mg/kg (with adrenaline 1:200,000)2–5 minutes1–2 hours (plain); 2–4 hours (with adrenaline)Moderate
BupivacaineAmide2 mg/kg (maximum 150 mg)5–15 minutes4–12 hours (peripheral); up to 24 hours (prolonged)HIGH
LevobupivacaineAmide (S-enantiomer of bupivacaine)2 mg/kg (maximum 150 mg)5–15 minutes4–12 hoursLOWER than bupivacaine
RopivacaineAmide (pure S-enantiomer)3 mg/kg (maximum 200 mg)5–15 minutes4–12 hoursLOWER than bupivacaine
PrilocaineAmide6 mg/kg (8 mg/kg with adrenaline)2–5 minutes1–2 hours (plain); 2–4 hours (with adrenaline)Low
CocaineEster1.5 mg/kg topical (maximum 200 mg)2–5 minutes (topical)30–45 minutesHIGH
Tetracaine (Amethocaine)Ester1.5 mg/kg30–45 minutes (topical gel)4–6 hours (topical)High

Lidocaine (Lignocaine)

AmideModerate cardiotoxicity
Available Concentrations
0.5%, 1%, 2%
Max Dose (plain)
3 mg/kg (without adrenaline); 7 mg/kg (with adrenaline 1:200,000)
Example (70 kg)
210 mg plain (70 kg); 490 mg with adrenaline
Onset
2–5 minutes
Duration
1–2 hours (plain); 2–4 hours (with adrenaline)
Metabolism
Hepatic (CYP3A4); active metabolites
pKa
7.9
Protein Binding
65%
Lipid Solubility
Moderate
Clinical Uses
IV regional anaesthesia (Bier block)Topical anaesthesiaShort peripheral nerve blocksEpidural anaesthesiaInfiltrationIV antiarrhythmic (ventricular arrhythmias)
Most versatile LA. Also used IV as antiarrhythmic and analgesic. AVOID for prolonged blocks. Rapid absorption — careful with intercostal blocks.

Bupivacaine

AmideHIGH cardiotoxicity
Available Concentrations
0.25%, 0.5%, 0.75% (spinal only)
Max Dose (plain)
2 mg/kg (maximum 150 mg)
Example (70 kg)
140 mg for 70 kg (2 mg/kg)
Onset
5–15 minutes
Duration
4–12 hours (peripheral); up to 24 hours (prolonged)
Metabolism
Hepatic; half-life 3.5 hours
pKa
8.1
Protein Binding
95%
Lipid Solubility
High
Clinical Uses
Peripheral nerve blocksEpidural anaesthesia and analgesiaSpinal anaesthesia (0.5% hyperbaric)Local infiltrationFascial plane blocks
Excellent long-acting anaesthesia. RACEMIC MIXTURE — l-isomer (levobupivacaine) is preferred when available. NEVER give IV. Cardiotoxic — irreversible cardiac sodium channel binding at overdose.

Levobupivacaine

Amide (S-enantiomer of bupivacaine)LOWER than bupivacaine cardiotoxicity
Available Concentrations
0.25%, 0.5%, 0.75%
Max Dose (plain)
2 mg/kg (maximum 150 mg)
Example (70 kg)
140 mg for 70 kg
Onset
5–15 minutes
Duration
4–12 hours
Metabolism
Hepatic
pKa
8.1
Protein Binding
97%
Lipid Solubility
High
Clinical Uses
Peripheral nerve blocksEpidural anaesthesia and analgesiaSpinal anaesthesiaFascial plane blocksPreferred over bupivacaine in UK clinical practice
Preferred over racemic bupivacaine in UK practice. Reduced CNS and cardiovascular toxicity compared to bupivacaine at equivalent doses. Same clinical efficacy.

Ropivacaine

Amide (pure S-enantiomer)LOWER than bupivacaine cardiotoxicity
Available Concentrations
0.2%, 0.375%, 0.5%, 0.75%, 1%
Max Dose (plain)
3 mg/kg (maximum 200 mg)
Example (70 kg)
210 mg for 70 kg
Onset
5–15 minutes
Duration
4–12 hours
Metabolism
Hepatic (CYP1A2)
pKa
8.1
Protein Binding
94%
Lipid Solubility
High (but less than bupivacaine)
Clinical Uses
Peripheral nerve blocksEpidural anaesthesia and labour analgesia (0.2%)Fascial plane blocksRegional anaesthesia requiring sensory/motor differentiation
Good sensory/motor separation (especially at lower concentrations 0.2%). Mildly vasoconstrictive intrinsically. Safer than bupivacaine — preferred for large volume blocks. Higher maximum dose than bupivacaine.

Prilocaine

AmideLow cardiotoxicity
Available Concentrations
0.5%, 1%, 2%, 4%
Max Dose (plain)
6 mg/kg (8 mg/kg with adrenaline)
Example (70 kg)
420 mg plain for 70 kg
Onset
2–5 minutes
Duration
1–2 hours (plain); 2–4 hours (with adrenaline)
Metabolism
Hepatic AND pulmonary; faster metabolism than lidocaine
pKa
7.9
Protein Binding
55%
Lipid Solubility
Moderate
Clinical Uses
EMLA cream (eutectic mixture with lidocaine)Intravenous regional anaesthesia (Bier block) — preferred agentDental proceduresTopical anaesthesia
LOWER systemic toxicity than lidocaine — preferred for Bier block. Metabolite o-toluidine causes METHAEMOGLOBINAEMIA at high doses (>600 mg). Avoid in G6PD deficiency, haemoglobin disorders, methhaemoglobinaemia.

Cocaine

EsterHIGH cardiotoxicity
Available Concentrations
4%, 10% (topical only)
Max Dose (plain)
1.5 mg/kg topical (maximum 200 mg)
Example (70 kg)
105 mg for 70 kg
Onset
2–5 minutes (topical)
Duration
30–45 minutes
Metabolism
Plasma esterases and hepatic
pKa
8.7
Protein Binding
91%
Lipid Solubility
High
Clinical Uses
ENT nasal procedures (unique: vasoconstriction + anaesthesia)Nasal septal proceduresONLY topical agent with vasoconstriction
ONLY LA with vasoconstriction property (inhibits NA reuptake). Topical use only. Controlled drug — Schedule II. Contraindicated in hypertension, cardiovascular disease, MAOIs.

Tetracaine (Amethocaine)

EsterHigh cardiotoxicity
Available Concentrations
0.5%, 1% (gel 4%)
Max Dose (plain)
1.5 mg/kg
Example (70 kg)
Limited by high systemic toxicity
Onset
30–45 minutes (topical gel)
Duration
4–6 hours (topical)
Metabolism
Plasma esterases (pseudocholinesterase)
pKa
8.5
Protein Binding
75%
Lipid Solubility
High
Clinical Uses
Ametop gel (4%) — topical paediatric use for venepuncture/cannulationOphthalmic anaesthesia dropsSpinal anaesthesia (historical)
AMETOP GEL: Apply 1g/1.5g to skin 30–45 minutes before procedure. Onset faster than EMLA. Causes localised erythema due to mast cell release (not allergy). Max 1 hour application in infants.
Adjuvants
Adrenaline (Epinephrine)
Add to LA solution; usually 1:200,000
Benefits
  • Prolongs block duration by 30–50%
  • Reduces peak plasma LA concentration
  • Reduces bleeding in infiltration
  • Test dose marker (intravascular injection: HR >20 bpm rise)
Cautions
  • NEVER use in digital blocks, penile blocks, ear/nose — vasoconstriction causes ischaemia
  • NEVER use in ankle/foot blocks
  • Use with caution in cardiac disease, hypertension
  • Avoid in areas with end-arteries
  • Cocaine + adrenaline = CONTRAINDICATED (combined catecholamine effect)
Dexamethasone
Perineural: 4–8 mg; IV: 4–8 mg (may be equivalent)
Benefits
  • Prolongs peripheral nerve block duration by 4–8 hours
  • Reduces postoperative nausea and vomiting
  • Anti-inflammatory analgesia
Cautions
  • Perineural use is off-label in UK
  • Caution in diabetic patients (transient hyperglycaemia)
  • IV dexamethasone may be equivalent to perineural (meta-analysis data)
Clonidine
50–150 mcg added to LA
Benefits
  • Prolongs block duration by 2–4 hours
  • Reduces postoperative opioid consumption
Cautions
  • Sedation
  • Hypotension
  • Bradycardia
  • Less reliable than dexamethasone