Determination of methacycline in human plasma by liquid chromatography coupled to tandem mass spectrometry

A rapid, sensitive and selective LC-MS-MS method has been developed and validated for the determination of methacycline in human plasma and employed in a bioequivalence study of two 300 mg tablet formulations in 18 healthy volunteers. The analyte and internal standard (IS) oxytetracycline were extracted from plasma using solid-phase extraction (SPE), then separated on a Diamonsil C18 column using a mobile phase of methanol-water-formic acid (80:20:0.5, v/v/v). The detection was performed on a tandem mass spectrometer equipped with an electrospray ionization (ESI) source. Linearity was established in the concentration range of 5.0-4000 ng/ml. The lower limit of quantification (LLOQ) was 5.0 ng/ml. The intra- and inter-day relative standard deviation (R.S.D.) across three validation runs over the entire concentration range was <8.0%. Accuracy determined at three concentrations (5.0, 200 and 3600 ng/ml for methacycline) ranged from 0.4 to 1.7% as terms of relative error (R.E.). Each plasma sample was chromatographed within 3.6 min. The method is proved to be highly selective and suitable for bioequivalence evaluation of different formulations containing methacycline and clinical pharmacokinetic investigation of methacycline.