What is the onset and duration of action of bupivacaine in epidural anesthesia?

Bupivacaine Onset and Duration in Epidural Anesthesia

Bupivacaine has a rapid onset of less than 15 minutes and provides prolonged anesthesia lasting up to 9 hours after epidural administration, with a period of residual analgesia extending beyond the return of sensation. 1, 2

Onset of Action

• The onset of epidural anesthesia with bupivacaine is rapid, occurring within 15 minutes or less 2
• Peak plasma concentrations are reached in 30 to 45 minutes following epidural injection 1
• When using lower concentrations (0.08% vs 0.5%), the mean onset of analgesia may be slightly delayed from approximately 9 minutes to 14 minutes, though this maintains efficacy while reducing adverse effects 3

Duration of Action

• Sensory block duration extends up to 9 hours after epidural administration of doses ≤202.5 mg bupivacaine 2
• The duration is significantly longer than any other commonly used local anesthetic 1
• A notable period of residual analgesia persists after the return of sensation, during which the need for strong analgesics is reduced 1
• When epinephrine 1:300,000 is added to bupivacaine, the duration of analgesia is significantly prolonged (approximately 178 minutes versus 132 minutes without epinephrine) 4

Concentration-Specific Dosing for Epidural Use

Lumbar Epidural in Adults

• Initial dose: 0.5 ml/kg of 0.25% bupivacaine (maximum 15 ml) 5, 6
• Higher concentrations (0.75%) provide pronounced motor blockade in over 90% of patients 7

Thoracic Epidural in Adults

• Initial dose: 0.2-0.3 ml/kg of 0.25% bupivacaine (maximum 10 ml) 5, 6

Pediatric Populations

• Maximum dose: 1 ml/kg of 0.25% bupivacaine (equivalent to 2.5 mg/kg) 5, 6
• For caudal block: 1.0 ml/kg of 0.25% bupivacaine 5, 6

Important Clinical Considerations

Epinephrine (1:200,000 or 5 mcg/mL) reduces the rate of absorption and peak plasma concentration, permitting moderately larger total doses and sometimes prolonging duration of action 1

Common Pitfalls to Avoid

• Incremental dosing is necessary to avoid unintended intravascular injection, which can lead to cardiovascular toxicity including atrioventricular block, ventricular arrhythmias, and cardiac arrest 1
• The most common adverse event is hypotension (occurring in 31% of patients), requiring vigilant monitoring 2
• For patients weighing less than 40 kg, calculate doses carefully; for obese patients, use ideal body weight 6
• Elderly patients reach maximal spread of analgesia and motor blockade more rapidly, exhibit higher peak plasma concentrations, and have decreased total plasma clearance 1

Pharmacokinetic Profile

• Elimination half-life: 2.7 hours in adults, 8.1 hours in neonates 1
• High protein binding capacity (95%) results in low fetal/maternal ratio (0.2-0.4) 1
• Plasma concentrations decline to insignificant levels over 3-6 hours following epidural administration 1