Determination of rimantadine in rat plasma by liquid chromatography/electrospray mass spectrometry and its application in a pharmacokinetic study

A rapid and sensitive liquid chromatography/mass spectrometry (LC/MS) method was developed and validated for the determination of rimantadine in rat plasma. Rimantadine was extracted by protein precipitation with methanol, and the chromatographic separation was performed on a C18 column. The total analytical run time was relatively short (4.6 min), and the limit of assay quantification (LLOQ) was 2 ng/mL using 50 μL of rat plasma. Rimantadine and the internal standard (amantadine) were monitored in selected ion monitoring (SIM) mode at m/z 180.2 and 152.1, respectively. The standard curve was linear over a concentration range from 2 to 750 ng/mL, and the correlation coefficients were greater than 0.999. The mean intra- and inter-day assay accuracy ranged from 100.1–105.0% to 100.3–104.0%, respectively, and the mean intra- and inter-day precision was between 1.3–2.3% and 1.8–3.0%, respectively. The developed assay method was successfully applied to a pharmacokinetic study in rats after oral administration of rimantadine hydrochloride at the dose of 20 mg/kg.