Orally bioavailable pyridine and pyrimidine-based Factor XIa inhibitors: Discovery of the methyl N-phenyl carbamate P2 prime group.

Pyridine-based Factor XIa (FXIa) inhibitor (S)-2 was optimized by modifying the P2 prime, P1, and scaffold regions. This work resulted in the discovery of the methyl N-phenyl carbamate P2 prime group which maintained FXIa activity, reduced the number of H-bond donors, and improved the physicochemical properties compared to the amino indazole P2 prime moiety. Compound (S)-17 was identified as a potent and selective FXIa inhibitor that was orally bioavailable. Replacement of the basic cyclohexyl methyl amine P1 in (S)-17 with the neutral p-chlorophenyltetrazole P1 resulted in the discovery of (S)-24 which showed a significant improvement in oral bioavailability compared to the previously reported imidazole (S)-23. Additional improvements in FXIa binding affinity, while maintaining oral bioavailability, was achieved by replacing the pyridine scaffold with either a regioisomeric pyridine or pyrimidine ring system.

Synthesis and Preliminary Evaluation of Phenyl 4-123I-Iodophenylcarbamate for Visualization of Cholinesterases Associated with Alzheimer Disease Pathology.

UNLABELLED: Acetylcholinesterase and butyrylcholinesterase accumulate with brain ß-amyloid (Aß) plaques in Alzheimer disease (AD). The overall activity of acetylcholinesterase is found to decline in AD, whereas butyrylcholinesterase has been found to either increase or remain the same. Although some cognitively normal older adults also have Aß plaques within the brain, cholinesterase-associated plaques are generally less abundant in such individuals. Thus, brain imaging of cholinesterase activity associated with Aß plaques has the potential to distinguish AD from cognitively normal older adults, with or without Aß accumulation, during life. Current Aß imaging agents are not able to provide this distinction. To address this unmet need, synthesis and evaluation of a cholinesterase-binding ligand, phenyl 4-(123)I-iodophenylcarbamate ((123)I-PIP), is described. METHODS: Phenyl 4-iodophenylcarbamate was synthesized and evaluated for binding potency toward acetylcholinesterase and butyrylcholinesterase using enzyme kinetic analysis. This compound was subsequently rapidly radiolabeled with (123)I and purified by high-performance liquid chromatography. Autoradiographic analyses were performed with (123)I-PIP using postmortem orbitofrontal cortex from cognitively normal and AD human brains. Comparisons were made with an Aß imaging agent, 2-(4'-dimethylaminophenyl)-6-(123)I-iodo-imidazo[1,2-a]pyridine ((123)I-IMPY), in adjacent brain sections. Tissues were also stained for Aß and cholinesterase activity to visualize Aß plaque load for comparison with radioligand uptake. RESULTS: Synthesized and purified PIP exhibited binding to cholinesterases. (123)I was successfully incorporated into this ligand. (123)I-PIP autoradiography with human tissue revealed accumulation of radioactivity only in AD brain tissues in which Aß plaques had cholinesterase activity. (123)I-IMPY accumulated in brain tissues with Aß plaques from both AD and cognitively normal individuals. CONCLUSION: Radiolabeled ligands specific for cholinesterases have potential for use in neuroimaging AD plaques during life. The compound herein described, (123)I-PIP, can detect cholinesterases associated with Aß plaques and can distinguish AD brain tissues from those of cognitively normal older adults with Aß plaques. Imaging cholinesterase activity associated with Aß plaques in the living brain may contribute to the definitive diagnosis of AD during life.

Low-frequency sonophoresis enhances rivastigmine permeation in vitro and in vivo.

We investigated the enhancement effect of low-frequency sonophoresis on transdermal permeation of rivastigmine in vitro and in vivo. The in vitro permeation study showed that sonophoresis increased steady-state transdermal flux 0.31 ± 0.03 µg x cm(-2) x h(-1) and the extent of rivastigmine permeation 6.00 ± 0.56 µg x cm(-2) though excised skin (both P < 0.01). In the in vivo experiment, the C(max) 0.83 ± 0.16 µg x mL(-1) and AUC(0 --> 24 h) 12.35 ± 1.99 µg x h x mL(-1) of the sonophoresis group was also significantly higher than that of the control group (both P < 0.01). These data suggest that low-frequency sonophoresis could be an effective method to enhance rivastigmine permeation.

Multitarget fatty acid amide hydrolase/cyclooxygenase blockade suppresses intestinal inflammation and protects against nonsteroidal anti-inflammatory drug-dependent gastrointestinal damage.

The ability of nonsteroidal anti-inflammatory drugs (NSAIDs) to inhibit cyclooxygenase (Cox)-1 and Cox-2 underlies the therapeutic efficacy of these drugs, as well as their propensity to damage the gastrointestinal (GI) epithelium. This toxic action greatly limits the use of NSAIDs in inflammatory bowel disease (IBD) and other chronic pathologies. Fatty acid amide hydrolase (FAAH) degrades the endocannabinoid anandamide, which attenuates inflammation and promotes GI healing. Here, we describe the first class of systemically active agents that simultaneously inhibit FAAH, Cox-1, and Cox-2 with high potency and selectivity. The class prototype 4: (ARN2508) is potent at inhibiting FAAH, Cox-1, and Cox-2 (median inhibitory concentration: FAAH, 0.031 ± 0.002 µM; Cox-1, 0.012 ± 0.002 µM; and Cox-2, 0.43 ± 0.025 µM) but does not significantly interact with a panel of >100 off targets. After oral administration in mice, ARN2508 engages its intended targets and exerts profound therapeutic effects in models of intestinal inflammation. Unlike NSAIDs, ARN2508 causes no gastric damage and indeed protects the GI from NSAID-induced damage through a mechanism that requires FAAH inhibition. Multitarget FAAH/Cox blockade may provide a transformative approach to IBD and other pathologies in which FAAH and Cox are overactive.

Impact of electrospray ion source platforms on matrix effect due to plasma phospholipids in the determination of rivastigmine by LC-MS/MS.

BACKGROUND: This study evaluates the performance of three electrospray ionization source designs to monitor the interference of plasma phospholipids for reliable estimation of rivastigmine by LC-MS/MS for method ruggedness. The variation in the area response due to matrix effects was assessed by post-column infusion, post-extraction spiking and standard-line slope methods. RESULTS: The observed interference due to coeluting phospholipids (m/z: 524.0/184.0) at the retention time of rivastigmine was 39.5, 12.9 and 0.4% using angular spray, orthogonal spray and dual orthogonal ion source spray design, respectively. Similarly, %CV for standard line slopes was 6.9, 4.6 and 2.0, respectively. CONCLUSION: Z-spray source design provided better and efficient transfer of gas phase ions into the mass analyzer compared with angular and orthogonal spray. The study showed that Z-spray ion source provided minimum interference from phospholipids compared with other ion source designs.

Transdermal rivastigmine in the treatment of Alzheimer's disease: current and future directions.

Despite the fact that the prevalence of Alzheimer's disease (AD) is exponentially increasing, we have not yet been able to develop a new treatment to modify the course of the disease. This vacuum makes the traditional cholinesterase inhibitors and N-methyl-D-aspartate receptor antagonist the only accessible pharmacotherapy options for the treatment of this disease. Among these medications, the only available transdermal patch at this time is the rivastigmine patch. This patch provides significantly lower gastrointestinal adverse effects. A higher tolerability rate provides the option for physicians to continue treatment with higher doses of rivastigmine in advanced stages of AD. Moreover, ease of use, easy-to-follow schedule, less administration time spent by the caregiver result in greater adherent to the treatment. This article aims to provide a comprehensive drug profile for transdermal rivastigmine, to review currently available treatment options, and to try to anticipate future treatment directions for AD.

Determination of Meserine, a new candidate for Alzheimer's disease in mice brain by liquid chromatography-tandem mass spectrometry and its application to a pharmacokinetic and tissue distribution study.

A rapid and sensitive liquid chromatography-tandem mass spectrometry (LC-MS/MS) method for determination of Meserine ((-)-meptazinol phenylcarbamate), a novel potent inhibitor of acetylcholinesterase (AChE), was developed, validated, and applied to a pharmacokinetic study in mice brain. The lower limit of quantification (LLOQ) was 1 ng mL(-1) and the linear range was 1-1,000 ng mL(-1). The analyte was eluted on a Zorbax SB-Aq column (2.1 × 100 mm, 3.5 µm) with the mobile phase composed of methanol and water (70:30, v/v, aqueous phase contained 10 mM ammonium formate and 0.3% formic acid) using isocratic elution, and monitored by positive electrospray ionization in multiple reaction monitoring (MRM) mode. The flow rate was 0.25 mL min(-1). The injection volume was 5 µL and total run time was 4 min. The relative standard deviation (RSD) of intraday and interday variation was 2.49-7.81 and 3.01-7.67%, respectively. All analytes were stable after 4 h at room temperature and 6 h in autosampler. The extraction recoveries of Meserine in brain homogenate were over 90%. The main brain pharmacokinetic parameters obtained after intranasal administration were T max = 0.05 h, C max = 462.0 ± 39.7 ng g(-1), T 1/2 = 0.4 h, and AUC(0-∞) = 283.1 ± 9.1 ng h g(-1). Moreover, Meserine was distributed rapidly and widely into brain, heart, liver, spleen, lung, and kidney tissue. The method is validated and could be applied to the pharmacokinetic and tissue distribution study of Meserine in mice.

Determination of a novel carbamate AChE inhibitor meserine in mouse plasma, brain and rat plasma by LC-MS/MS: application to pharmacokinetic study after intravenous and subcutaneous administration.

In this paper a simple and sensitive method for determination of a novel phenylcarbamate AChE inhibitor, meserine, in mouse plasma, brain and rat plasma was evaluated using high-performance liquid chromatography-tandem mass spectrometry (LC-MS/MS). Separation was achieved on an Alltech Alltima-C18 column (150mm×2.1mm, 3µm, Deerfield, IL, USA) with isocratic elution at a flow rate of 0.35ml/min. Detection was performed under the multiple reaction monitoring (MRM) mode using an electrospray ionization (ESI) in the positive ion mode. The protein precipitation and liquid-liquid extraction methods were used for the pretreatment of plasma and brain homogenates, respectively. The calibration curves of meserine showed good linearity over the concentration range of 0.5-1000ng/ml for mouse and rat plasma and 0.5-500ng/ml for mouse brain. The intra- and inter-day precision were less than 9.34% and the accuracy was from 95.34% to 107.78% for QC samples. The validated method was successfully applied to a preclinical pharmacokinetic study of meserine in mice and rats after intravenous and subcutaneous administration. The results showed that this novel drug could easily cross the blood-brain barrier to reach the site of drug action. Meserine was rapidly absorbed with a high subcutaneous absolute bioavailability (>90%).

Novel L-lactide-depsipeptide polymeric carrier for enhanced brain uptake of rivastigmine in treatment of Alzheimer's disease.

The present study discusses possibility of targeting an anti-Alzheimer's drug rivastigmine tartarate (RT) to the brain using novel synthesized L-lactide-depsipeptide polymeric nanoparticles (NPs). Single emulsion-solvent evaporation technique was used for preparation of NPs. The mean particle size, zeta potential and entrapment efficiency of drug loaded NPs were found to be 142.2 +/- 21.3 nm, +4.85 mV and 60.72 +/- 3.72% respectively. Pharmacodynamic study showed faster regain of memory loss in amnesic rat with RT loaded NPs as compared to RT solution. In pharmacokinetic study, total concentration and mean residence time was increased up to 3.79 fold and 2 fold respectively while clearance was decreased to 1.91 fold on intravenous administration of RT loaded NPs as compared to RT solution. The biodistribution study demonstrated 5.45 fold and 2 fold increase in brain concentration of drug after administration of RT loaded NPs (i.v; 10.52 +/- 1.31 ng/ml) as compared to plain RT solution by oral (1.93 +/- 1.23 ng/ml) and intravenous (5.34 +/- 1.22 ng/ml) route, respectively. Therefore, RT loaded L-lactide-depsipeptide polymeric NPs might be a potential drug delivery system in treatment of Alzheimer's disease.

Drugs for cognitive loss and dementia.

The drugs currently available for the treatment of Alzheimer's disease and other dementias can provide limited symptomatic improvement. The acetylcholinesterase inhibitors donepezil, rivastigmine, and galantamine and the NMDA-receptor antagonist memantine have produced modest but apparently persistent improvements in cognition, activities of daily living, and behavior in patients with disease severity ranging from mild to severe. Among the acetylcholinesterase inhibitors, transdermal rivastigmine causes fewer gastrointestinal side effects than the oral formulation. Whether adding memantine to an acetylcholinesterase inhibitor is more effective than an acetylcholinesterase inhibitor alone remains to be established; clinical trial results have been mixed. None of these agents have been shown to stop or reverse the underlying neurodegenerative process.

Enhanced brain distribution and pharmacodynamics of rivastigmine by liposomes following intranasal administration.

Alzheimer's disease (AD) is a common progressive neurodegenerative disorder associated with cholinergic neurons degeneration. The blood-brain barrier (BBB) not only provides protection for the brain but also hinders the treatment and diagnosis of this neurological disease, because the drugs must cross BBB to reach the lesions. The present work was aimed at formulating rivastigmine liposomes (Lp) and cell-penetrating peptide (CPP) modified liposomes (CPP-Lp) to improve rivastigmine distribution in brain and proceed to enhance pharmacodynamics by intranasal (IN) administration and minimize side effects. The results revealed that Lp especially the CPP-Lp can enhance the permeability across the BBB by murine brain microvascular endothelial cells model in vitro. IN administration of rivastigmine solution and rivastigmine liposomes demonstrated the capacity to improve rivastigmine distribution and adequate retention in CNS regions especially in hippocampus and cortex, which were the regions most affected by AD, than that of IV administration. Importantly, the lagging but intense inhibition of acetylcholinesterase (AChE) and butyrylcholinesterase (BuChE) activities were relative to the extended release, absorption and retention. In addition, there was very mild nasal toxicity of liposomal formulations. The data suggest that rivastigmine liposomes especially CPP-Lp improve the brain delivery and enhance pharmacodynamics which respect to BBB penetration and nasal olfactory pathway into brain after IN administration, and simultaneously decrease the hepatic first pass metabolism and gastrointestinal adverse effects.

Potential therapeutic effect of nanobased formulation of rivastigmine on rat model of Alzheimer's disease.

BACKGROUND: To sustain the effect of rivastigmine, a hydrophilic cholinesterase inhibitor, nanobased formulations were prepared. The efficacy of the prepared rivastigmine liposomes (RLs) in comparison to rivastigmine solution (RS) was assessed in an aluminium chloride (AlCl(3))-induced Alzheimer's model. METHODS: Liposomes were prepared by lipid hydration (F1) and heating (F2) methods. Rats were treated with either RS or RLs (1 mg/kg/day) concomitantly with AlCl(3) (50 mg/kg/day). RESULTS: The study showed that the F1 method produced smaller liposomes (67.51 ± 14.2 nm) than F2 (528.7 ± 15.5 nm), but both entrapped the same amount of the drug (92.1% ± 1.4%). After 6 hours, 74.2% ± 1.5% and 60.8% ± 2.3% of rivastigmine were released from F1 and F2, respectively. Both RLs and RS improved the deterioration of spatial memory induced by AlCl(3), with RLs having a superior effect. Further biochemical measurements proved that RS and RLs were able to lower plasma C-reactive protein, homocysteine and asymmetric dimethy-larginine levels. RS significantly attenuated acetylcholinesterase (AChE) activity, whereas Na(+)/K(+)-adenosine triphosphatase (ATPase) activity was enhanced compared to the AlCl(3)-treated animals; however, RLs succeeded in normalization of AChE and Na(+)/K(+) ATPase activities. Gene-expression profile showed that cotreatment with RS to AlCl(3)-treated rats succeeded in exerting significant decreases in BACE1, AChE, and IL1B gene expression. Normalization of the expression of the aforementioned genes was achieved by coadministration of RLs to AlCl(3)-treated rats. The profound therapeutic effect of RLs over RS was evidenced by nearly preventing amyloid plaque formation, as shown in the histopathological examination of rat brain. CONCLUSION: RLs could be a potential drug-delivery system for ameliorating Alzheimer's disease.

Pharmacodynamic, pharmacokinetic and pharmacogenetic aspects of drugs used in the treatment of Alzheimer's disease.

With the aging population and its rapidly increasing prevalence, dementia has become an important public health concern in developed and developing countries. To date, the pharmacological treatment is symptomatic and based on the observed neurotransmitter disturbances. The four most commonly used drugs are donepezil, galantamine, rivastigmine and memantine. Donepezil, galantamine and rivastigmine are acetylcholinesterase inhibitors with different pharmacodynamic and pharmacokinetic profiles. Donepezil inhibits selectively the acetylcholinesterase and has a long elimination half-life (t(1/2)) of 70 h. Galantamine is also a selective acetylcholinesterase inhibitor, but also modulates presynaptic nicotinic receptors. It has a t(1/2) of 6-8 h. Donepezil and galantamine are mainly metabolised by cytochrome P450 (CYP) 2D6 and CYP3A4 in the liver. Rivastigmine is a so-called 'pseudo-irreversible' inhibitor of acetylcholinesterase and butyrylcholinesterase. The t(1/2) of the drug is very short (1-2 h), but the duration of action is longer as the enzymes are blocked for around 8.5 and 3.5 h, respectively. Rivastigmine is metabolised by esterases in liver and intestine. Memantine is a non-competitive low-affinity antagonist of the NMDA receptor with a t(1/2) of 70 h. Its major route of elimination is unchanged via the kidneys. Addressing the issue of inter-patient variability in treatment response might be of special importance for the vulnerable population taking anti-dementia drugs. Pharmacogenetic considerations might help to avoid multiple medication changes due to non-response and/or adverse events. Some pharmacogenetic studies conducted on donepezil and galantamine reported an influence of the CYP2D6 genotype on the pharmacokinetics of the drugs and/or on the response to treatment. Moreover, polymorphisms in genes of the cholinergic markers acetylcholinesterase, butyrylcholinesterase, choline acetyltransferase and paraoxonase were found to be associated with better clinical response to acetylcholinesterase inhibitors. However, confirmation studies in larger populations are necessary to establish evidence of which subgroups of patients will most likely benefit from anti-dementia drugs. The aim of this review is to summarize the pharmacodynamics and pharmacokinetics of the four commonly used anti-dementia drugs and to give an overview on the current knowledge of pharmacogenetics in this field.

Buccoadhesive films for once-a-day administration of rivastigmine: systematic formulation development and pharmacokinetic evaluation.

CONTEXT: Rivastigmine, an anti-Alzheimer's drug, suffers from major predicaments like low oral bioavailability, severe GI adverse effects related to rapid fluctuations in drug plasma levels, and high frequency of dosing. OBJECTIVE: The present investigation aims at developing buccoadhesive films capable of delivering the drug in vivo in a sustained manner. Augmentation of drug bioavailability by the avoidance of first-pass effect through the buccal route and reduction in GI side effects would be other key advantages of this system. METHODS: Buccoadhesive films of rivastigmine were systematically designed and evaluated for in vitro drug release, ex vivo buccal permeation and ex vivo buccoadhesive strength. Optimal composition of the polymer blends was rationally chosen using a central composite design and overlay plot. In vivo pharmacokinetic studies were carried out in rabbits, and attempts were made to establish in vitro/ in vivo correlations (IVIVC). RESULTS: Besides possessing the requisite drug release regulation, the optimized formulation exhibited excellent buccoadhesion, and buccal permeation. Pharmacokinetic studies indicated extension of plasma drug levels and level A of IVIVC was successfully established. DISCUSSION: Excellent buccal bioadhesion and transmucosal permeation, coupled with drug release control, ratify the potential of the optimized formulation to deliver the drug in a controlled and site-specific manner. Successful establishment of IVIVC substantiated the judicious choice of in vitro dissolution media for simulating the in vivo conditions. CONCLUSION: Besides unraveling the polymer synergism, the study helped in developing an optimal once-a-day buccoadhesive drug delivery system exhibiting excellent trans-buccal permeation and buccoadhesive characteristics with improved bioavailability potential.

Amphiphilic polyaspartamide copolymer-based micelles for rivastigmine delivery to neuronal cells.

A novel polysorbate-80 (PS(80))-attached amphiphilic copolymer comprising a hydrophilic α,ß-poly(N-2-hydroxyethyl)-D,L-aspartamide (PHEA) backbone and hydrophobic squalenyl-C(17) (Sq(17)) portions was synthesized and characterized; the formation of polymeric micelles was also evaluated. Rivastigmine free-base (Riv), a hydrophobic drug employed to treat Alzheimer's disease, was chosen as model drug to investigate micelle's ability to incorporate hydrophobic molecules and target them to neuronal cells. Micelle formation was studied through analyses including fluorescence spectroscopy and 2D (1)H-NMR NOESY experiments. Finally, the capacity of Riv-loaded micelles, versus free drug, to penetrate mouse neuroblastoma cells (Neuro2a) was evaluated. 2D (1)H-NMR NOESY experiments demonstrated that the PHEA-EDA-Sq(17)-PS(80) copolymer self-assembles into micelle structures in water, with a micelle core formed by hydrophobic interaction between Sq(17) alkyl chains. Fluorescence probe studies revealed the CAC of PHEA-EDA-Sq(17)-PS(80) micelles, which was 0.25 mg mL(-1). The micelles obtained had a nanometric hydrodynamic diameter with narrow size distribution and negative surface charge. The PHEA-EDA-Sq(17)-PS(80) micelles incorporated a large amount of Riv, and the system maintained the stability of Riv after incubation in human plasma. An in vitro biological assay evidenced no cytotoxic effects of either empty or loaded micelles on the neuronal cell lines tested. Moreover, the micelles are internalized by neuroblastoma cell lines with drug uptake depending on the micelles concentration.

Development and evaluation of rivastigmine loaded chitosan nanoparticles for brain targeting.

The rivastigmine (RHT) loaded chitosan nanoparticles (CS-RHT NPs) were prepared by ionic gelation method to improve the bioavailability and enhance the uptake of RHT to the brain via intranasal (i.n.) delivery. CS-RHT NPs were characterized for particles size, particle size distribution (PDI), encapsulation efficiency, zeta potential and in vitro release study. Nose-to-brain delivery of placebo nanoparticles (CS-NPs) was investigated by confocal laser scanning microscopy technique using rhodamine-123 as a marker. The brain/blood ratio of RHT for different formulations were 0.235, 0.790 and 1.712 of RHT (i.v.), RHT (i.n.), and CS-RHT NPs (i.n.) respectively at 30 min are indicative of direct nose to brain transport bypassing the BBB. The brain concentration achieved from i.n. administration of CS-NPs (966 ± 20.66 ng ml(-1); t(max) 60 min) was significantly higher than those achieved after i.v. administration of RHT sol (387 ± 29.51 ngml(-1); t(max) 30 min), and i.n. administration of RHT solution (508.66 ± 22.50 ng ml(-1); t(max) 60 min). The higher drug transport efficiency (355 ± 13.52%) and direct transport percentage (71.80 ± 6.71%) were found with CS-RHT NPs as compared to other formulation. These results suggest that CS-RHT NPs have better brain targeting efficiency and are a promising approach for i.n. delivery of RHT for the treatment and prevention of Alzheimer's disease (AD).

Tissue distribution and pharmacodynamics of rivastigmine after intranasal and intravenous administration in rats.

The aim of the study was mainly to investigate the relationship between concentration of rivastigmine and its inhibition of acetylcholinesterase (AChE) and butyrylcholinesterase (BuChE) following intranasal (IN) and intravenous (IV) administration in rats, and to provide a novel nasal delivery route for the brain disease therapy. Rivastigmine was administered to male rats at 2 mg/kg by IN and IV route. Drug concentration, AChE and BuChE activity were measured in the plasma, central nervous system (CNS) regions i.e. olfactory region, hippocampus, cerebrum and cerebellum, and peripheral tissues. It was determined that rivastigmine was characterized by extremely rapid and complete absorption into the systemic circulation followed by a rapid decline in the plasma concentrations, and can also quickly distribute into CNS and peripheral tissues by the two routes. IN administration showed higher concentration in CNS regions and longer action on inhibiting the activity of AChE and BuChE than IV administration. More significant decrease of the two enzymes was observed in CNS regions than in peripheral tissues for both administrations. A close relationship was found between the concentration of rivastigmine and enzyme inhibition in plasma and CNS tissues in rats. Based on these findings, it was concluded that rivastigmine could cause relatively strong inhibition of AChE and BuChE in plasma and brain tissues, especially in hippocampus, cortex and cerebrum. The pharmacodynamics was closely related to its concentration in vivo. The intranasal route can be strategy for delivering the drug into brain.

[Preparation of rivastigmine liposome and its pharmacokinetics in rats after intranasal administration].

To prepare rivastigmine liposome, rivastigmine was loaded into liposome via ammonium sulfate gradient method. Its pharmacokinetic profile in rats was evaluated after intranasal administration. The size, zeta potential, entrapped efficiency and release of rivastigmine from the liposome in vitro were determined. Plasma concentration of rivastigmine was determined by high performance liquid chromatography-tandem mass spectrometry (HPLC/MS) using antipyrine as internal standard. The pharmacokinetic parameters were calculated by DAS 2.0. The entrapped efficiency of rivastigmine liposome was (33.41 +/- 6.58) %, with the mean diameter of 154-236 nm and zeta potential of (-10.47 +/- 2.41) mV. The release behavior of rivastigmine was fitting the first order equation in vitro. The pharmacokinetic studies indicated that the C(max), T(max) and AUC(0-infinity), of rivastigmine liposome were (1.50 +/- 0.15) mg x L(-1), 15 min and (89.06 +/- 8.30) mg x L(-') x min, respectively. Rivastimine liposome was absorbed rapidly, and could reach a certain concentration in rat plasma after intranasal delivery.

Bioequivalence evaluation of two brands of rivastigmine of different salt forms, an acetylcholinesterase inhibitor for the treatment of Alzheimer's disease, in healthy Beagle dogs.

The bioequivalence of two brands of rivastigmine capsules, of different salt forms, was demonstrated in six healthy beagle dogs after a single oral dose in a randomized cross-over study. Reference (Rivastigmine hydrochloride, Sunve, CN) and test (Rivastigmine tartrate, Novartis, CH) products were administered to fasting beagles on two treatment days separated by a two-day washout period; blood samples were collected at specified time intervals, and the plasma was separated and analyzed for rivastigmine using a validated GC-MS method. The pharmacokinetic parameters AUC(0-t), AUC(0-infinity), C(max), T(max) and t1/2 were compared statistically to evaluate bioequivalence between the two brands, using the statistical modules recommended by the State Food and Drug Administration (SFDA) of China. The analysis of variance (ANOVA) did not show any significant difference between the two formulations and 90% confidence intervals fell within the acceptable ranges for bioequivalence. Based on these statistical inferences it was concluded that the two brands exhibited comparable pharmacokinetic profiles and that Sanwei's Rivastigmine hydrochloride was bioequivalent to Rivastigmine tartrate of Novartis, CH.