Evaluationof the Bromcresol Purplemethodfor Albuminas Used with the Aca

Lidocaine is a frequently administered anti-arrhythmic drug, particularly useful in emergency situations because of its rapid onset of action (1). Therapeutic drug monitoring of lidocaine is recommended because of its potent central nervous system toxicity. Moreover, lidocaine has been implicated in numerous accidental and homicidal deaths (2). Thus its chemical stability in patients’ specimens and in quality-control specimens needs to be known. Two metabolites of lidocaine, monoethylglicinexylidide and glycinexylidide, are unstable in plasma and urine (3), but no work has been published on the stability of lidocaine itself. Therefore, we have assessed the stability of lidocaine in serum and blood. Sera from patients being treated with lidocaine were pooled and stored at -20 #{176}C until used. Cadaver blood containing lidocaine was also collected and pooled. After an initial quantification by gas chromatography (4), the serum and blood were each divided into two portions.One was stored at 25 #{176}C, the other at 4#{176}C. At various time intervals, aliquots of fluid stored ateach temperature were removed and re-assayed. After 70 days, at least 80% of the lidocaine was detected in serum at either temperature. Furthermore, no changes in blood lidocaine concentration were detected over a similar time period at either temperature. Any changes in lidocaine concentration were within the out-of-run CV of the method. We conclude that lidocaine is quite stable in serum and blood over a twoto three-month period.