Answer:
The introduction of standard tumescent solution in 1987 has allowed the development of liposuction as a procedure that can be performed under local anesthesia alone with reduced risks of lidocaine toxicity. The standard solution is usually a 0.05% lidocaine solution in the following formulation:
1000 cc normal saline
25 cc 2% lidocaine (500 mg)
1 cc 1:1000 epinephrine (1:1,000,000)
12.5 cc 8.4% bicarbonate
The dilution and infusion of the solution is thought to change the pharmokinetics of lidocaine such that doses much higher than the standard 5-7 mg/kg can be tolerated. A dose of 35 mg/kg has been reported to result in plasma levels of 3-4 mcg/ml. Lidocaine toxicity is thought to be much more likely beyond levels of 6 mcg/ml. Recently, doses as high as 66 mg/kg have been reported to be safe. Toxicity when it has occurred has been thought to result from drug interactions interfering with lidocaine metabolism by the hepatic cytochrome P450 pathway. Many common drugs including cimetidine, erythromycin, nifedipine, methadone, thyroxine, verapamil, valproic acid, and midazolam can interfere with lidocaine metabolism.