What is the onset of action of bupivacaine (local anesthetic)?

Onset of Action of Bupivacaine

Bupivacaine has a rapid onset of action, typically beginning within 5-15 minutes after administration, with full anesthetic effect developing within 15-30 minutes depending on the site of injection. 1

Pharmacodynamics and Onset

Bupivacaine is a long-acting amide local anesthetic that works by blocking the generation and conduction of nerve impulses. The onset of action depends on several factors:

• Mechanism of action: Bupivacaine increases the threshold for electrical excitation in nerves, slows nerve impulse propagation, and reduces the rate of rise of the action potential 1
• Progression of anesthesia: The order of nerve function loss is: (1) pain, (2) temperature, (3) touch, (4) proprioception, and (5) skeletal muscle tone 1
• Site of administration: Onset varies by injection site and technique (infiltration, peripheral nerve block, epidural, etc.)

Onset Times by Administration Route

• Epidural administration: Sensory block develops within 10-15 minutes 2
• Intrathecal (spinal) administration: Sensory block develops within 10-15 minutes, with maximal spread between T1-T2 2
• Peripheral nerve blocks: Onset within 15 minutes 3
• Local infiltration: Rapid onset, typically within minutes 1

Factors Affecting Onset

Several factors can influence the onset time of bupivacaine:

• Concentration: Higher concentrations generally provide faster onset
• Addition of epinephrine: May slightly delay systemic absorption but can prolong duration 1
• Patient factors: Age, weight, and cardiovascular status can affect onset
• Formulation: Standard vs. liposomal formulations (liposomal formulations have similar onset but prolonged duration) 4, 5

Duration of Action

While not specifically about onset, it's important to note that bupivacaine has a long duration of action:

• Duration range: 180-600 minutes (3-10 hours) 2
• Maximum doses:
  • Without epinephrine: 2.5 mg/kg (medical), 1.3 mg/kg (dental) 2
  • With epinephrine: 3.0 mg/kg 2

Clinical Implications

• When planning procedures, allow at least 15 minutes for full effect to develop before beginning painful stimuli
• For time-sensitive procedures, consider factors that might accelerate onset (proper technique, optimal concentration)
• Monitor for systemic toxicity, especially during the onset period when absorption is highest
• For pediatric patients, dosing should be adjusted according to weight with maximum doses of 2.5 mg/kg without epinephrine 2

Safety Considerations

• Cardiovascular and CNS toxicity can occur with high plasma concentrations 1
• Careful aspiration before injection is essential to minimize intravascular administration 2
• Have resuscitation equipment and 20% lipid emulsion available when using higher doses 2
• Onset of toxicity symptoms can occur rapidly after inadvertent intravascular injection

Bupivacaine's relatively rapid onset combined with its long duration of action makes it a valuable option for procedures requiring extended analgesia or anesthesia.