Gas chromatographic determination of mexiletine in human plasma with flame ionization detection after reaction with carbon disulphide

Gas chromatography-electron ionization and chemical ionization mass spectrometric analysis of serum mexiletine concentration after derivatization with 2,2,2-trichloroethyl chloroformate: a novel derivative

Mexiletine (Mexitil) is an antiarrhythmic agent used in the treatment of ventricular arrhythmia. The drug has a narrow therapeutic window, and monitoring its serum concentration is recommended. The authors describe a gas chromatography-mass spectrometric (GC/MS) assay of mexiletine using selected ion monitoring. Mexiletine was extracted from alkaline serum with dichloromethane followed by derivatization with 2,2,2-trichloroethyl chloroformate. The reaction was completed in 30 minutes at 70 degrees C. N-propylamphetamine was used as the internal standard. The ions monitored were m/z 58, 102, 122, 232, and 234 for derivatized mexiletine and m/z 56, 91, 131, 260, and 262 for the derivatized internal standard. The within-run precision at a serum mexiletine concentration of 1 mg/l was 1.7% (mean = 0.981, SD = 0.017 mg/l, n = 8) and the between-run precision was 3.3% (mean = 0.983, SD = 0.033 mg/l, n = 6). The assay was linear for serum mexiletine concentrations of 0.2 to 2.5 mg/l. The detection limit was 0.1 mg/l. The authors observed no carry-over problem in their assay. They observed a good correlation between mexiletine concentrations measured by a reference laboratory (Associated Regional University Pathologists, Salt Lake City, UT, U.S.A.) and by the new GC/MS assay.

Gas chromatographic-mass spectrometric determination of serum mexiletine concentration after derivatization with perfluorooctanoyl chloride, a new derivative

Mexiletine is an antiarrhythmic agent used in the treatment of ventricular arrhythmia. The drug has a narrow therapeutic window which necessitates monitoring its serum concentrations. We describe a gas chromatographic-mass spectrometric analysis of mexiletine using selected ion monitoring. Mexiletine was extracted from alkaline serum with dichloromethane and then derivatized with perfluorooctanoyl chloride. The derivatization reaction was completed in 20 min at 80 degrees C. We used N-propylamphetamine as the internal standard. The ions monitored were m/z 122, 454 and 575 for the derivatized mexiletine and m/z 91, 118, 440 and 452 for the derivatized internal standard. The within-run precision at a serum mexiletine concentration of 1 mg/l was 1.9% (mean=0.98, S.D.=0.019 mg/l, n=7) and the between-run precision was 2.5% (mean=0.99, S.D.=0.025 mg/l, n=7). The assay was linear for serum mexiletine concentrations of 0.2 to 4 mg/l. The detection limit was 0.1 mg/l. The average recoveries of mexiletine and the internal standard were 80% and 84%, respectively at a mexiletine concentration of 1 mg/l. There was no carry over problem in our assay. We observed a good correlation between mexiletine concentrations measured by a reference laboratory (GC) and by our new GC-MS assay.

Determination of plasma mexiletine levels with gas chromatography-mass spectrometry and selected-ion monitoring

Mexiletine, 1-(2,6-dimethylphenoxy)-2-aminopropane (Mexitil), is an orally effective agent useful in the treatment of serious ventricular arrhythmias. This paper describes a gas chromatographic-mass spectrophotometric assay with selected-ion monitoring for the measurement of plasma or serum mexiletine levels. The drug and internal standard (p-chlorophenylalanine methyl ester) were extracted from plasma into ethyl acetate-hexane-methanol (60:40:1, v/v). After separation and evaporation of the organic phase, the drug and internal standard were derivatized to their pentafluoropropyl derivatives prior to analysis. The reproducibility of the daily standard curve yielded mean inter- and intra-day coefficients of variability from 0.7 to 11.0%. The coefficients of variability for control plasma samples (0.5 and 1.0 micrograms/ml) ranged from 2.6 to 5.0% and the accuracy of the assay was 106 +/- 6 and 100 +/- 5% for the low and high level controls respectively. The limit of quantitation for the assay was 0.1 micrograms/ml. No interfering peaks were detected in any patient samples. This method can be used as a primary analytical method to measure mexiletine plasma levels or can serve as a convenient back-up method to HPLC procedures when contaminating peaks coelute with mexiletine.