Bupivacaine

Bupivacaine (rINN) is a local anaesthetic drug belonging to the amino amide group. AstraZeneca commonly markets it under various trade names, including Marcain, Marcaine,Sensorcaine and Vivacaine.

Indications
Bupivacaine is indicated for local anaesthesia including infiltration, nerve block, epidural, and intrathecal anaesthesia. Bupivacaine often is administered by epidural injection before total hip arthroplasty. It also is commonly injected to surgical wound sites to reduce pain for up to 20 hours after the surgery. Sometimes, bupivacaine is co-administered with adrenaline to prolong the duration of its action, fentanyl for epidural analgesia, or glucose.

Contraindications
Bupivacaine is contraindicated for IV regional anaesthesia (IVRA) because of potential risk of tourniquet failure and systemic absorption of the drug.

Adverse effects
Compared to other local anaesthetics, bupivacaine is markedly cardiotoxic. However, adverse drug reactions (ADRs) are rare when it is administered correctly. Most ADRs relate to administration technique (resulting in systemic exposure) or pharmacological effects of anesthesia, however allergic reactions can rarely occur.

Systemic exposure to excessive quantities of bupivacaine mainly result in central nervous system (CNS) and cardiovascular effects – CNS effects usually occur at lower blood plasma concentrations and additional cardiovascular effects present at higher concentrations, though cardiovascular collapse may also occur with low concentrations. CNS effects may include CNS excitation (nervousness, tingling around the mouth, tinnitus, tremor, dizziness, blurred vision, seizures) followed by depression (drowsiness, loss of consciousness, respiratory depression and apnea). Cardiovascular effects include hypotension, bradycardia, arrhythmias, and/or cardiac arrest – some of which may be due to hypoxemia secondary to respiratory depression.

Bupivacaine has caused several deaths when the epidural anaesthetic has been administered intravenously accidentally.

Treatment of overdose: lipid rescue
There is animal evidence that Intralipid, a commonly available intravenous lipid emulsion, can be effective in treating severe cardiotoxicity secondary to local anaesthetic overdose, and human case reports of successful use in this way. Schemes to publicise this use more widely have been published.

Mechanism of action
Bupivacaine binds to the intracellular portion of sodium channels and blocks sodium influx into nerve cells, which prevents depolarization. Since pain transmitting nerve fibres tend to be thinner and either unmyelinated or lightly myelinated, the agent can diffuse more readily into them than into thicker and more heavily myelinated nerve fibres like touch, proprioception, etc. (Myelin is non-polar / lipophilic).

Developments
Levobupivacaine is the S(-)-enantiomer of bupivacaine, with a longer duration of action and produces less vasodilation. Durect Corporation is developing a biodegradable controlled-release drug delivery system for post surgery. It is currently in Phase II.