Bupivacaine

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Bupivacaine is an amide-type local anaesthetic. It has a slow onset but long duration of action. It is commonly used in concentrations of 0.125% to 0.75%. The reason that the concentration can be lower than lidocaine is because of the higher lipid solubility leading to higher potency. Higher concentrations generally have a faster onset of action. The onset of action is approximately 8 to 12 minutes for simple blocks of small nerves.

It binds to plasma proteins and has a plasma half-life of 1.5-5.5 hours. It is largely metabolised in the liver.

It is the most cardiotoxic of all the local anaesthetics especially if inadvertently given intravenously. The cardiotoxic effect is enhanced by hypoxia, hypercapnia, acidosis, and hyperkalaemia. Ventricular fibrillation is a risk due to inhibition of cardiac conductivity and contractility. It should be avoided in patients with cardiac disease. The toxic dose of bupivacaine is only 80 mg which is 16 mL of a 0.5% solution when given intravascularly, but may be up to 225 mg with extravascular injection.