High-performance liquid chromatography with ultraviolet and fluorimetric detection for the simultaneous determination of tacrine, nimodipine, and their respective metabolites in the plasma of patients with Alzheimer disease

Analysis of acetylcholinesterase inhibitors: bioanalysis, degradation and metabolism

Alzheimer's is a neurodegenerative disease. Its symptoms are attributed to a deficiency of cholinergic neurotransmission. The drugs of choice for the treatment of Alzheimer's disease are acetylcholinesterase (AChE) inhibitors. Starting in the 1980's from non-specific AChE inhibitors, the first-generation drugs such as physostigmine, a second generation of more selective and better tolerated products has been developed. Methods to detect and quantify these drugs and their metabolites in biological samples have been developed for analysis in plasma, blood, urine and cerebrospinal fluid. Diverse detection techniques have been used, such as ultraviolet, fluorescence, electrochemical and mass spectrometry. In this review, the methods applied to the analysis of these drugs and their metabolites in different biological matrices are reviewed and discussed. The stability of these drugs in biological matrices and under stress-conditions is also included in the discussion.

Determination of nimodipine in plasma by HPLC-MS/MS and pharmacokinetic application

To develop and validate a rapid, specific and highly sensitive method to quantify nimodipine in human plasma using dibucaine as the internal standard (IS). The analyte and IS were extracted from plasma samples by liquid-liquid extraction using hexane-ethyl acetate (1:1 v/v). The chromatographic separation was performed on a Varian® Polaris C18 analytical column (3 μm, 50 x 2.0 mm) and pre-column SecurityguardTM C18 (4.0 x 3.0 mm) with a mobile phase of Acetonitrile-Ammonium acetate 0.02 ml/L (80:20v/v). The method had a chromatographic run time of 4.5 min and linear calibration curve over the range of 0.1- 40 ng/mL (r > 0.9938). The limit of quantification was 100 pg/mL. Acceptable precision and accuracy were obtained for concentrations over the standard curve ranges. This validated method was successfully applied in determining the pharmacokinetic profile of nimodipine tablets of 30 mg administered to 24 healthy volunteers. The proposed method of analysis provided a sensitive and specific assay for nimodipine determination in human plasma. The time for the determination of one plasma sample was 4.5 min. This method is suitable for the analysis of nimodipine in human plasma samples collected for pharmacokinetic, bioavailability or bioequivalence studies in humans.

Determination of nimodipine in human plasma by a sensitive and selective liquid chromatography–tandem mass spectrometry method

A sensitive and highly selective liquid chromatography-tandem mass spectrometry (LC-MS-MS) method was developed to determine nimodipine in human plasma. The analyte and internal standard nitrendipine were extracted from plasma samples by n-hexane-dichloromethane-isopropanol (300:150:4, v/v/v), and chromatographed on a C(18) column. The mobile phase consisted of methanol-water-formic acid (80:20:1, v/v/v). Detection was performed on a triple quadrupole tandem mass spectrometer by selected reaction monitoring (SRM) mode via atmospheric pressure chemical ionization (APCI) source. The method has a limit of quantification of 0.24 ng/ml. The linear calibration curves were obtained in the concentration range of 0.24-80 ng/ml. The intra- and inter-day precisions were lower than 4.4% in terms of relative standard deviation (R.S.D.), and the accuracy ranged from 0.0 to 5.8% in terms of relative error (RE). This validated method was successfully applied for the evaluation of pharmacokinetic profiles of nimodipine tablets administered to 18 healthy volunteers.

Spectrofluorimetric determination of velnacrine in human serum and urine

A simple, sensitive and rapid spectrofluorimetric method to determine velnacrine, a cholinesterase inhibitor, has been developed and validated. The influence of pH, temperature, ionic strength, presence of excipients, metal ions and surfactants on the fluorescence intensity has been studied. The proposed method allows the determination of 5-100 ng ml(-1) of velnacrine in aqueous solution containing sodium acetate buffer (pH 5.6; 0.04 M) with lambda(excitation) 242 nm and lambda(emission) 359 nm. The detection and quantitation limits were 1.7 and 4.5 ng ml(-1) respectively. The method was successfully applied to the determination of velnacrine in human serum and urine.

Therapeutic drug monitoring of tacrine: simple and fast high-performance liquid chromatography assay method for its determination in human plasma

A new high-performance liquid chromatography (HPLC) assay method was developed for the therapeutic monitoring of tacrine. The method involved a simple protein precipitation by means of either acetonitrile or cold methanol followed by a fast isocratic separation on a CN column eluted in reversed-phase mode. The entire sample preparation took place in an HPLC vial and no further liquid transfer was required. The validation data showed that the assay method was precise, accurate, and robust. Analysis of more than 1,000 plasma samples collected from patients with Alzheimer disease demonstrates the suitability of the assay.