Sensitive high-performance liquid chromatographic assay using 9-fluorenylmethylchloroformate for monitoring controlled-release lidocaine in plasma

A sensitive high-performance liquid chromatographic (HPLC) assay using fluorescence detection for quantifying lidocaine levels in plasma (in the ng/ml range) was developed. This novel HPLC assay has made possible the simultaneous monitoring of lidocaine levels in coronary and peripheral plasma obtained after myocardial controlled-release matrix administration (0.92 mg/kg during 4 h) in the arrhythmic dog. The method employed extracts the drug from plasma using 1-chlorobutane and a subsequent derivatization with 9-fluorenylmethylchloroformate in acetonitrile at 110°C. The derivative was chromatographed on a C₁₈ reversed-phase column and measured with fluorescence detection (excitation 254 nm, emission 313 nm). N-Methylephedrine was found to be suitable as an internal standard, post-derivatization. The derivatization product of lidocaine was identified and characterized by mass spectral analysis. It was found to have a unique and reproducible dicarbamate structure, which was stable for at least three days at room temperature. The method was tested with human plasma as well as on dog plasma. Analytical recoveries were 88.6 ± 3.6 and 77.4 ± 3.0% (mean ± S.E.), respectively, at levels ranging from 25 to 200 ng/ml. The lower detection limit was 1 ng/ml lidocaine. In conclusion, this rapid and convenient analysis was found to be suitable for the bioavailability pharmacokinetic assessment of lidocaine following low-dose regional drug administration.