high-performance liquid chromatographic determination of rivastig-mine in human plasma for application in pharmacokinetic studies

a simple and reproducible hplc method with spectrophotometric detection was developed for determination of rivastigmine in human plasma. liquid-liquid extraction of rivastigmine and donepezil (as internal standard) from plasma samples was performed with 1-butanol/n-hexane (2:98 v/v) in alkaline condition followed by back-extraction into diluted acetic acid. chromatography was carried out using a silica column (250 mm × 4.6 mm, 5 µm) under isocratic elution with acetonitrile-50 mm aqueous sodium dihydrogen phosphate (17: 83 v/v, ph 3.1. analyses were run at a flow-rate of 1.3 ml/min at of 50°c. the recovery was 90.8% and 95.7% for rivastigmine and the internal standard donepezil, respectively. the precision of the method was 2.6% to 9.1% over the concentration range of 0.5-16 ng/ml for rivastigmine in plasma with a linearity greater than 0.999. the method was specific and sensitive, with a quantification limit of 0.5 ng/ml and a detection limit of 0.2 ng/ml in plasma. the method was used for a bioequivalence study in healthy subjects.