To evaluate the effect of a pseudo-carrier (9-hydroxypropyl-(+)-dihydrotetrabenazine, AV-149) on pharmacokinetics of 9-fluoropropyl-(+)-dihydrotetrabenazine (AV-133), an ultra-performance liquid chromatography–tandem mass spectrometric (UPLC–MS/MS) method was developed and validated for the determination of AV-133 and AV-149 in rat plasma. AV-133 and AV-149 were extracted from plasma following protein precipitation. The chromatographic analysis was performed on an ACQUITY UPLC BEH™ C18 column (50 mm × 2.1 mm × 1.7 μm) by a gradient elution. The mass spectrometer was operated in positive mode using electrospray ionization. The analytes were measured using the multiple reaction-monitoring mode (MRM). An external calibration was used, and the calibration curves were linear in the range of 1.00–800 ng/mL for AV-133 and AV-149. The accuracy ranged from 90.8% to 113.2% and the precision ranged from 2.7% to 9.9% for each analyte. The effect of a pseudo-carrier on pharmacokinetics of AV-133 was studied using the presented method.

To evaluate the penetration of the blood–brain barrier by 9-fluoropropyl-(+)-dihydrotetrabenazine (AV-133), microdialysis probes were implanted simultaneously into rat blood and brain, and a liquid chromatography–tandem mass spectrometric method was developed and validated to monitor the AV-133 concentration in the microdialysates. The chromatographic separation was performed on an XTerra C18 column (150 mm × 2.1 mm i.d., 5 μm particles) with gradient elution. The mass spectrometer was operated in positive mode using electrospray ionization. The analytes were measured using the multiple-reaction-monitoring mode. The calibration curves were linear over the range of 5.00–1000 ng/mL AV-133, with a coefficient of determination >0.995. The accuracies ranged from 99.5% to 105.0% and the precisions were <10% for AV-133. This method was used to determine the concentrations of AV-133 and its pharmacokinetics in the brains and blood of rats. The blood and brain concentration–time profiles for AV-133 were obtained, and the blood–brain barrier penetration was evaluated.

This study proposed a stress testing to study oxidative stability and estimate the potential shelf-life of l,l-ethylenedicysteine (l,l-EC) under normal storage temperature condition (20–25 °C). l,l-EC was detected as a function of time at four different temperatures by ultra-performance liquid chromatography/tandem mass spectrometry (UPLC/MS/MS). The degradation of l,l-EC followed the first order kinetics, and the temperature-dependent kinetics was well described by the linear Arrhenius equation. The activation energy (Ea) was calculated, and the shelf-life at 25 and 4 °C was predicted. The results are useful for the proper storage and quality evaluation of l,l-EC.