Investigation into MAO B-Mediated Formation of CC112273, a Major Circulating Metabolite of Ozanimod, in Humans and Preclinical Species: Stereospecific Oxidative Deamination of (S)-Enantiomer of Indaneamine (RP101075) by MAO B.

Ozanimod, recently approved for treating relapsing multiple sclerosis, produced a disproportionate, active, MAO B-catalyzed metabolite (CC112273) that showed remarkable interspecies differences and led to challenges in safety testing. This study explored the kinetics of CC112273 formation from its precursor RP101075. Incubations with human liver mitochondrial fractions revealed K Mapp, V max, and intrinsic clearance (Clint) for CC112273 formation to be 4.8 µM, 50.3 pmol/min/mg protein, and 12 µl/min/mg, respectively, whereas Michaelis-Menten constant (K M) with human recombinant MAO B was 1.1 µM. Studies with liver mitochondrial fractions from preclinical species led to K Mapp, V max, and Clint estimates of 3.0, 35, and 33 µM, 80.6, 114, 37.3 pmol/min/mg, and 27.2, 3.25, and 1.14 µl/min/mg in monkey, rat, and mouse, respectively, and revealed marked differences between rodents and primates, primarily attributable to differences in the K M Comparison of Clint estimates revealed monkey to be ∼2-fold more efficient and the mouse and rat to be 11- and 4-fold less efficient than humans in CC112273 formation. The influence of stereochemistry on MAO B-mediated oxidation was also investigated using the R-isomer of RP101075 (RP101074). This showed marked selectivity toward catalysis of the S-isomer (RP101075) only. Docking into MAO B crystal structure suggested that although both the isomers occupied its active site, only the orientation of RP101075 presented the C-H on the α-carbon that was ideal for the C-H bond cleavage, which is a requisite for oxidative deamination. These studies explain the basis for the observed interspecies differences in the metabolism of ozanimod as well as the substrate stereospecificity for formation of CC112273. SIGNIFICANCE STATEMENT: This study evaluates the enzymology and the species differences of the major circulating metabolite of ozanimod, CC112273. Additionally, the study also explores the influence of stereochemistry on MAO B-catalyzed reactions. The study is of significance to the DMD readers given that this oxidation is catalyzed by a non-cytochrome P450 enzyme, and that marked species difference and notable stereospecificity was observed in MAO B-catalyzed biotransformation when the indaneamine enantiomers were used as substrates.

Simple determination of some antidementia drugs in wastewater and human plasma samples by tandem dispersive liquid-liquid microextraction followed by high-performance liquid chromatography.

In this work, a simple method, namely, tandem dispersive liquid-liquid microextraction, with a high sample clean-up is applied for the rapid determination of the antidementia drugs rivastigmine and donepezil in wastewater and human plasma samples. This method, which is based on two consecutive dispersive microextractions, is performed in 7 min. In the method, using a fast back-extraction step, the applicability of the dispersive microextraction methods in complicated matrixes is conveniently improved. This step can be performed in less than 2 min, and very simple tools are required for this purpose. To achieve the best extraction efficiency, optimization of the variables affecting the method was carried out. Under the optimized experimental conditions, the relative standard deviations for the method were in the range of 6.9-8.7%. The calibration curves were obtained in the range of 2-1100 ng/mL with good correlation coefficients, higher than 0.995, and the limits of detection ranged between 0.5 and 1.0 ng/mL.

Long Acting Ionically Paired Embonate Based Nanocrystals of Donepezil for the Treatment of Alzheimer's Disease: a Proof of Concept Study.

PURPOSE: The aim of the present study was to prepare a patient friendly long acting donepezil (D) nanocrystals (NCs) formulation, with a high payload for i.m administration. As the native D hydrochloride salt has high aqueous solubility it is necessary to increase its hydrophobicity prior to the NCs formation. METHODS: D was ionically paired with embonic acid (E) in aqueous media and was successfully characterized using techniques like DSC, PXRD, FT-IR, NMR etc. Later, we converted the bulk ion pair into NCs using high pressure homogenization technique to study further in-vitro and in-vivo. RESULTS: The bulk ion pair has a drug content of 66% w/w and an 11,000 reduced solubility in comparison to native D hydrochloride. Also, its crystalline nature was confirmed by DSC and PXRD. The possible interaction sites responsible for the ion pair formation were identified though NMR. The prepared NCs has mean particle size 677.5 ± 72.5 nm and PDI 0.152 ± 0.061. In-vitro release showed a slow dissolution of NCs. Further, excellent bio compatibility of NCs were demonstrated in 3T3 cells. Following i.m administration of single dose of NCs, the D plasma level was found to be detectable up to 18 days. In vivo pharmacodynamic studies revealed that the single dose NCs i.m injection improved spatial memory learning and retention in ICV STZ model. CONCLUSION: Our results suggest that the developed formulation has a potential to replace the current daily dosing regimen to a less frequent dosing schedule. Graphical Abstract Improved pharmacokinetic and pharmacodynamic profile after administration of single dose donpezil embonate nanocrystals in Rats.

Effect of chongmyungtang, a traditional Korean polyherbal formula, on the Pharmacokinetic profiles of donepezil in rats.

Chongmyungtang (CMT) is a famous Korean herbal medicine for improving learning and memory, which has been reported to have anti-cholinergic and neuroprotective effects. Therefore, drug-drug interactions were examined between CMT and donepezil as a first screening of combination therapy for cognitive deficits. Rats received oral co-administration of donepezil with distilled water as a control or donepezil with CMT as a combination. The distilled water or CMT was co-administered at intervals within 5min after donepezil or 1.5h intervals. The plasma samples were analyzed for donepezil concentration and its pharmacokinetic parameters of Tmax, Cmax, AUC, t1/2 and MRTinf. In the single co-administration at intervals within 5min, donepezil was detected lower in the combination than control at 0.5h and 2h post-treatment (P<0.05). In addition, the combination showed significant increases in MRTinf compared to the control (P<0.05). This suggests drug-drug interactions between donepezil and CMT in the co-administration within 5 min. However, no meaningful differences were found in the pharmacokinetic profiles of donepezil by single dosing with CMT at 1.5h intervals and even by the repeated dosing for a week at 1.5h intervals potential combination therapy of donepezil with CMT.

Local Drug-Drug Interaction of Donepezil with Cilostazol at Breast Cancer Resistance Protein (ABCG2) Increases Drug Accumulation in Heart.

Clinical reports indicate that cardiotoxicity due to donepezil can occur after coadministration with cilostazol. We speculated that the concentration of donepezil in heart tissue might be increased as a result of interaction with cilostazol at efflux transporters such as P-glycoprotein (P-gp, ABCB1) and breast cancer resistance protein (BCRP, ABCG2), which are expressed in many tissues including the heart, and our study tested this hypothesis. First, donepezil was confirmed to be a substrate of both BCRP and P-glycoprotein in transporter-transfected cells in vitro. Cilostazol inhibited BCRP and P-glycoprotein with half-inhibitory concentrations of 130 nM and 12.7 µM, respectively. Considering the clinically achievable unbound plasma concentration of cilostazol (about 200 nM), it is plausible that BCRP-mediated transport of donepezil would be affected by cilostazol in vivo. Indeed, in an in vivo rat study, we found that coadministration of cilostazol significantly increased the concentrations of donepezil in the heart and brain, where BCRP functions as a part of the blood-tissue barrier, whereas the plasma concentration of donepezil was unaffected. In addition, in vitro accumulation of donepezil in heart tissue slices of rats was significantly increased in the presence of cilostazol. These results indicate that donepezil-cilostazol interaction at BCRP may be clinically relevant in heart and brain tissues. In other words, the tissue distribution of drugs can be influenced by drug-drug interaction (DDI) at efflux transporters in certain tissues (local DDI) without any apparent change in plasma concentration (systemic DDI).

Monitoring Plasma Levels of Donepezil, 5-O-Desmethyl-Donepezil, 6-O-Desmethyl-Donepezil, and Donepezil-N-Oxide by a Novel HPLC Method in Patients With Alzheimer Disease.

BACKGROUND: In humans, donepezil (D) is metabolized to 5-O-desmethyl-donepezil (5DD), 6-O-desmethyl-donepezil (6DD), and donepezil-N-oxide (DNox). Although 6DD and DNox are pharmacologically active, the activity of 5DD is unknown. At present, no routine methods are available to detect D and its 3 metabolites simultaneously. In this study, a novel high-performance liquid chromatography method was developed and applied to a population of patients with Alzheimer disease on stable treatment with the drug. METHODS: Liquid-liquid extraction from plasma was accomplished by means of a solvent mixture of n-hexane/dichloromethane/ethylacetate (45:40:15) after sample alkalinization. Disopyramide was the internal standard. After evaporation, the residue was reconstituted in 200 µL of mobile phase (acetonitrile 85%:1% acetic acid 15%) and 50 µL was injected into the high-performance liquid chromatography column (X-Terra, RP8; flow: 1 mL/min). Photometric and fluorimetric detectors were used in tandem, to maximize the sensitivity of fluorescent compounds (D, 5DD, and DNox) and also to reveal nonfluorescent compounds (6DD and internal standard). RESULTS: The method was linear in the 10-100 ng/mL concentration range. Imprecision (coefficient of variation) varied between 3.2% and 12.6% and inaccuracy (% mean absolute error) between 1.3% and 13.3%, depending on the compound, concentration, and detection mode. The quantitation limits were 0.1-0.3 ng/mL for fluorescent compounds and 1.2-4.3 ng/mL for photometric compounds. D, 5DD, 6DD, and DNox through concentrations were measured in 54 patients with Alzheimer disease on treatment with D (10 mg q.d.). No interfering peaks by endogenous compounds or coadministered drugs were noted. Plasma concentrations were quite variable among patients (D: 10-106 ng/mL; 5DD: 0.07-2.8 ng/mL; 6DD: 1.2-36 ng/mL; DNox: 0.5-45.4 ng/mL). Of note, in 6 patients, the plasma concentrations of the 2 active metabolites (6DD and DNox) were higher than those of the parent drug. CONCLUSIONS: The above method proved to be suitable for therapeutic drug monitoring and may be useful in ascertaining the real contribution of metabolites to the therapeutic effects of donepezil.

Donepezil plasma concentrations, CYP2D6 and CYP3A4 phenotypes, and cognitive outcome in Alzheimer's disease.

PURPOSE: The purpose of the study is to evaluate whether donepezil (D) plasma concentrations and activity of CYP2D6 and CYP3A4 are associated with the therapeutic response of patients with mild to moderate Alzheimer's disease (AD). METHODS: This study comprised 54 patients affected by probable AD in therapy with D 10 mg/daily for at least 3 months. Plasma concentrations of D and its three main metabolites (6DD, 5DD, DNox) were assayed with a novel high performance liquid chromatography (HPLC) technique. Cognitive progression was assessed at baseline and at 9 months of follow-up with the mini mental state examination (MMSE). The activities of the two cytochromes involved in D metabolism-CYP2D6 and CYP3A4-were evaluated according to their metabolic ratios in plasma or urine, after test doses of probe drugs (dextromethorphan and omeprazole). RESULTS: A significant correlation was found between plasma levels of D and variations in MMSE scores after 9 months of therapy (r (2) = 0.14; p = 0.006). Neither the concentrations of D metabolites nor the metabolic ratios of CYP2D6 and CYP3A4 showed any correlations with cognitive variations. Low CYP2D6 activity and advanced age were associated with high D concentrations. Patients who were treated with CYP2D6 and P-glycoprotein (P-gp) inhibitors also had higher D plasma levels (mean difference = 19.6 ng/mL; p = 0.01) than those who were not. CONCLUSIONS: D plasma concentrations, but not cytochrome phenotyping, are associated with cognitive outcomes in AD patients.

Determination of donepezil in serum samples using molecularly imprinted polymer nanoparticles followed by high-performance liquid chromatography with ultraviolet detection.

A molecularly imprinted polymer designed for the selective extraction of donepezil from serum samples was synthesized using a noncovalent molecular imprinting approach. The molecularly imprinted polymer was evaluated chromatographically and then its affinity for donepezil was confirmed by solid-phase extraction. The optimal conditions for solid-phase extraction were provided by cartridge conditioning using acidified water purified from a Milli-Q system, sample loading under basic aqueous conditions, clean-up using acetonitrile, and elution with methanol/tetrahydrofuran. Desirable molecular recognition properties of the molecularly imprinted polymer led to good donepezil recoveries (90-102%). The data indicated that the imprinted polymer has a perfect selectivity and affinity for donepezil and could be used for selective extraction and analysis of donepezil in human serum.

Pharmacokinetic interaction study between flavanones (hesperetin, naringenin) and rasagiline mesylate in wistar rats.

Cytochrome P-450 (CYP) enzymes and P-glycoprotein (P-gp) play an important role in the oral bioavailability and first-pass-metabolism (FPM) of many drugs. Rasagiline is a selective, monoamine oxidase-B inhibitor and it undergoes significant FPM in the liver prior to excretion by CYP1A2. Hesperetin and naringenin are naturally occurring flavanones and are reported as modulators of CYP enzymes and P-gp. The objective of the present investigation was to evaluate the effect of hesperetin and naringenin on the pharmacokinetics (PK) of rasagiline in rats. Rats were treated orally with rasagiline (2 mg/kg) alone and co-administered with hesperetin and naringenin (12.5 and 25 mg/kg) for 15 consecutive days. Blood samples were collected from tail vein on the 1st day in a single dose PK study (SDS) and on 15th day in the multiple dose PK study (MDS). Hesperetin and naringenin co-administration significantly enhanced the area under the curve (AUC), maximum plasma concentration (Cmax) and elimination half life (t1/2) of rasagiline with a concomitant reduction in clearance (CL/F) in both SDS and MDS. Rasagiline concentrations were significantly increased when co-administered with hesperetin and naringenin in the brain. No significant difference was found in rasagiline transport from mucosal to serosal side in the presence of hesperetin and naringenin ex vivo (rat everted gut sacs used). Our findings suggested that hesperetin and naringenin enhanced the systemic exposure of rasagiline might be through the inhibition of CYP1A2 but not P-gp. Further studies are needed on CYP1A2 and P-gp over expressed cells to confirm this interaction at cellular level.

Therapeutic drug monitoring for patients with Alzheimer dementia to improve treatment with donepezil.

BACKGROUND: Aiming to verify that therapeutic drug monitoring has the potential to optimize treatment with acetylcholine esterase inhibitors of patients with Alzheimer dementia, this study investigated whether serum concentrations of donepezil are associated with clinical improvement. METHODS: Clinical improvement was measured using the clinical global impression (CGI) scale, and donepezil concentrations were measured in serum by a high-performance liquid chromatographic method with spectrophotometric detection. RESULTS: In total, 206 serum samples from 106 patients (49.5% female) were retrospectively available for analysis. Patients included were treated under everyday conditions. Their mean ± SD age was 72 ± 9 years, daily doses of donepezil were 5 and 10 mg, and their mean ± SD serum concentrations were 23 ± 9 and 47 ± 18 ng/mL, respectively. Serum concentrations correlated significantly (P < 0.001) with CGI scores (Pearson's correlation coefficient r = 0.511, P < 0.01). In patients who were "very much improved," according to their CGI score, the mean serum concentration was 66 ± 20 ng/mL and thus significantly higher (P < 0.01) than in patients with "minimal improvement" (29 ± 12 ng/mL). Receiver operating characteristics analysis suggests that donepezil serum concentrations of at least 50 ng/mL may be recommended for maximal clinical benefit. CONCLUSIONS: Because donepezil serum concentrations were highly variable between individual patients and the majority of patients exhibited concentrations that were below 50 ng/mL at therapeutic doses of 5 and 10 mg/d, it can be concluded that therapeutic drug monitoring may be used to enhance the effectiveness of donepezil treatment.

Stereoselective metabolism of donepezil and steady-state plasma concentrations of S-donepezil based on CYP2D6 polymorphisms in the therapeutic responses of Han Chinese patients with Alzheimer's disease.

The therapeutic response rates of patients to donepezil vary from 20% to 60%, one of the reasons is their genetic differences in donepezil-metabolizing enzymes, which directly influence liver metabolism. However, the mechanism of donepezil metabolism and that of its enantiomers is unknown. This study evaluated CYP2D6 polymorphisms to elucidate the stereoselective metabolism of donepezil and to confirm the association between the steady-state plasma concentrations of the pharmaco-effective S-donepezil and the therapeutic responses of Han Chinese patients with Alzheimer's disease. The in vitro study of the stereoselective metabolism demonstrated that CYP2D6 is the predominant P450 enzyme that metabolizes donepezil and that different CYP2D6 alleles differentially affect donepezil enantiomers metabolism. A total of 77 Han Chinese patients with Alzheimer's disease were recruited to confirm these results, by measuring their steady-state plasma concentrations of S-donepezil. The related CYP2D6 genes were genotyped. Plasma concentrations of S-donepezil (based on CYP2D6 polymorphisms) were significantly associated with therapeutic responses. This finding suggests that plasma concentrations of S-donepezil influence therapeutic outcomes following treatment with donepezil in Han Chinese patients with Alzheimer's disease. Therefore, determining a patient's steady-state plasma concentration of S-donepezil in combination with their CYP2D6 genotype might be useful for clinically monitoring the therapeutic efficacy of donepezil.

Therapeutic dosage assessment based on population pharmacokinetics of a novel single-dose transdermal donepezil patch in healthy volunteers.

PURPOSE: We performed population pharmacokinetic (PK) analysis of a novel transdermal donepezil patch in healthy subjects who participated in a phase I trial. We also studied the optimal dosage regimen with repeated patch application for achieving a therapeutic range using a PK simulation model. METHODS: This study used data from a randomized, single-dose escalation phase I clinical trial conducted in Korea. The population PK analysis was performed using NONMEM software, version 7.3. From the final PK model, we simulated repeat patch application results assuming various transdermal absorption rates. RESULTS: Based on the clinical trial data, novel donepezil patches with doses of 43.75 mg/12.5 cm(2), 87.5 mg/25 cm(2), and 175 mg/50 cm(2) were placed on each subject. A linear one-compartment, first-order elimination with sequential zero- and first-order absorption model best described the donepezil plasma concentrations after patch application. Simulated results on the basis of the PK model showed that repeat application of the patches of 87.5 mg/25 cm(2) and 175 mg/50 cm(2) every 72 h would cover the therapeutic range of donepezil and reach steady-state faster with fewer fluctuations in concentration compared to typical oral administrations. CONCLUSION: A linear one-compartment with sequential zero- and first-order absorption model was effective for describing the PKs of donepezil after application of patch. Based on this analysis, 87.5 mg/25 cm(2) or 175 mg/50 cm(2) patch application every 72 h is expected to achieve the desired plasma concentration of donepezil.

Pharmacokinetics of QMF149 in Japanese versus Caucasian subjects: an open-label, randomized phase I study.

OBJECTIVES: This study aimed to evaluate influence of ethnic factors on the pharmacokinetics of orally inhaled QMF149, a novel combination of an approved longacting ß2-agonist, indacaterol (Onbrez® Breezhaler® for COPD), and an approved inhaled corticosteroid, mometasone furoate (MF), (Asmanex® Twisthaler® for asthma), following multiple dose administration of QMF149 (indacaterol acetate/MF) 150/80 µg and 150/320 µg via the Breezhaler® device in healthy Japanese and Caucasian subjects. METHODS: This was a single-center, openlabel, multiple-dose, two-period, complete crossover study that randomized healthy Japanese and, age and weight matched Caucasian subjects to QMF149 150/80 µg or 150/320 µg once daily (o.d.) for 14 days in each period. Pharmacokinetics (PK) were assessed up to 24 hours on days 1 and 14. RESULTS: 24 Japanese and 24 Caucasian healthy subjects were enrolled. Indacaterol and MF had similar PK profiles across both the doses and both ethnic groups. The maximum geometric mean ratios (90% confidence interval (CI)) for Japanese vs. Caucasian subjects for Cmax were 1.23 (1.11 - 1.38) and 1.24 (1.11 - 1.38) for indacaterol and MF, respectively. For AUC, the maximum ratios were 1.22 (1.09 - 1.36) and 1.30 (1.18 - 1.44) for indacaterol and MF, respectively. The mild trend towards higher exposure in Japanese subjects could be explained by the fact that the mean body weight was 14% higher for Caucasians compared to their Japanese counterparts. No serious adverse events or discontinuations related to study medication were reported. CONCLUSION: The study demonstrated increase of mean exposure parameters in Japanese subjects vs. Caucasian subjects, which ranged between 19 - 23% and 17 - 30%, for indacaterol and MF components, respectively. Multiple doses of both the QMF149 dose levels were safe and well-tolerated in all subjects. Body weight was considered a key contributory factor for the observed difference in exposure. These results suggest no dose adjustment for QMF149 is required in Asian populations.

Impact of CYP2D6 and CYP3A4 genetic polymorphism on combined cholinesterase inhibitors and memantine treatment in mild to moderate Alzheimer's disease.

AIM: The impact of CYP2D6 and CYP3A4 polymorphism on the steady-state plasma concentrations and therapeutic outcome of donepezil monotherapy and combination therapy in Alzheimer's disease (AD) patients. METHODS: A total of 38 patients for donepezil and 17 patients for donepezil and memantine therapy, aged ≥ 55 years, were recruited meeting inclusion and exclusion criteria. Polymerase chain reaction-restriction fragment length polymorphism was performed. The liquid chromatography-tandem mass spectrometry method was used for estimation of drug levels of donepezil and memantine. RESULTS: Significant allele frequency was observed for CYP2D6*3 polymorphism in patients on donepezil monotherapy and combination therapy. Significant allele frequency for CYP2D6*4 was observed in the patients on donepezil monotherapy. CONCLUSION: CYP2D6 polymorphism, though not significant, might partially be involved in the plasma concentration of AD drug.

Effect of deprotenizing agent and quantification of donepezil hydrochloride in human plasma.

The effect of deprotenizing agents on recovery of donepezil hydrochloride in the development of a simple, rapid, selective and sensitive high performance liquid chromatography method for quantification of donepezil hydrochloride in human plasma was described. The deprotenizing agents were comprised of, perchloric acid, methanol, acetonitrile, chloroform and their mixtures. The chromatographic separation was carried out using reversed phase C18 column (Agilent Eclipse Plus C18) with UV detection at 268 nm. The mobile phase was comprised of 0.01 M potassium dihydrogen phosphate buffer, methanol and acetronitrile (50:30:20, v/v) adjusted to pH 2.7 with phosphoric acid (80%). A combination of perchloric acid and methanol gave a cleaner sample with a good recovery of donepezil hydrochloride of above 96%. The method showed intraday precision and accuracy in the range of 6.82% to 1.5% and 3.13% to 1.12% respectively, while interday precision and accuracy ranged between 1.06% to 4.71% and 13.01% to 6.43% respectively. The standard calibration curve was linear from 30ng/mL to 4000ng/mL, with a correlation coefficient of 0.9965±0.0034. The retention time of donepezil was 5.9 min with a run time of 7.0 min. The method can be applied to analyze large batch plasma samples in pharmacokinetic studies.

Trace analysis of acetylcholinesterase inhibitors with antipsychotic drugs for Alzheimer's disease by capillary electrophoresis with on column field-amplified sample injection.

A simple and sensitive capillary zone electrophoresis (CZE) with UV detection (214 nm) was developed and validated for the simultaneous determination of the acetylcholinesterase inhibitors (AChEI), donepezil, and rivastigmine, with antipsychotic drugs in plasma. A sample pretreatment by liquid-liquid extraction and subsequent quantification by CZE with field-amplified sample injection (FASI) was used. The optimum separation for these analytes was achieved in <20 min at 25 °C with a fused-silica capillary column of 60.2 cm × 50 µm I.D. (effective length 50 cm) and a run buffer containing 120 mM phosphate (pH 4.0) with 0.1 % γ-cyclodextrin, 40 % methanol (MeOH), and 0.02 % polyvinyl alcohol as a dynamic coating to reduce analytes' interaction with the capillary wall. Using phenformin as an internal standard (40.0 ng/mL), the linear ranges of the proposed method for the simultaneous determination of donepezil, rivastigmine, aripiprazole, quetiapine, risperidone, clozapine, ziprasidone, and trazodone were over the range 4.0-80.0 ng/mL, and olanzapine was over the range 1.0-20.0 ng/mL. The method was applied for concentrations monitoring of AChEIs and antipsychotic drugs in ten Alzheimer's disease patients with behavioral and psychological symptoms of dementia after oral administration of the commercial products.

Steady-state plasma concentration of donepezil enantiomers and its stereoselective metabolism and transport in vitro.

The aim of the present study was to elucidate the differences in the plasma concentration of two enantiomers of donepezil in Chinese patients with Alzheimer's disease (AD) and investigate in vitro stereoselective metabolism and transport. Donepezil enantiomers were separated and determined by LC-MS/MS using D5-donepezil as an internal standard on a Sepax Chiralomix SB-5 column. In vitro stereoselective metabolism and transport of donepezil were investigated in human liver microsomes and MDCKII-MDR1 cell monolayer. Pre-dose (Css-min) plasma concentrations were determined in 52 patients. The mean plasma level of (R)-donepezil was 14.94 ng/ml and that of (S)-donepezil was 23.37 ng/ml. One patient's plasma concentration of (R)-donepezil was higher than (S)-donepezil and the ratio is 1.51. The mean plasma levels of (S)-donepezil were found to be higher than those of (R)-donepezil in 51 patients and the ratio of plasma (R)- to (S)-donepezil varies from 0.34 to 0.85. In the in vitro microsomal system, (R)-donepezil degraded faster than (S)-donepezil. V(max) of (R)-donepezil was significantly higher than (S)-donepezil. The P-gp inhibition experiment shown that the P(app) of the two enantiomers was higher than 200 and the efflux ratios were 1.11 and 0.99. The results of the P-gp inhibition identification experiment showed IC50 values of 35.5 and 20.4 µM, respectively, for the two enantiomers. The results indicate that donepezil exhibits stereoselective hepatic metabolism that may explain the differences in the steady-state plasma concentrations observed. Neither (R)- nor (S)-donepezil was a P-gp substance and the two enantiomers are highly permeable through the blood-brain barrier.

Comparative single-dose pharmacokinetics of rasagiline in minipigs after oral dosing or transdermal administration via a newly developed patch.

1. A rasagiline transdermal patch was developed for the treatment of early and advanced Parkinson's disease. Relevant pharmacokinetic parameters of rasagiline obtained after transdermal administration to minipigs were compared with those of rasagiline after oral administration. 2. A total of 18 minipigs were randomly divided into three groups (six animals for each group). A single dose of 1 mg rasagiline tablet was orally administrated to one group. Meanwhile, single dose of 1.25 and 2.5 mg (2 and 4 cm(2)) rasagiline patches were given (at the postauricular skin) to the other two groups, respectively. The pharmacokinetic parameters such as plasma half-life (t1/2), time to peak plasma-concentration (Tmax), mean residence time (MRT), area under the curve (AUC(0-t)) were significantly (p < 0.05) different between transdermal and oral administrations. 3. The plasma half-life (t1/2) of rasagiline (1.25 mg patch: 11.8 ± 6.5 h, 2.5 mg patch: 12.5 ± 4.7 h) in minipig following transdermal administration was significantly prolonged as compared with that following the oral administration (1 mg tablet: 4.7 ± 2.5 h). The dose-normalized relative bioavailability of rasagiline patch in minipig were 178.5% and 156.4%, respectively, for 1.25 and 2.5 mg patches compared with 1 mg rasagiline tablet. The prolonged t1/2 and increased bioavailability of rasagiline patch suggested a possible longer dosing interval compared with oral tablet.

Metabolism and pharmacokinetics of indacaterol in humans.

The metabolism, pharmacokinetics, and excretion of [(14)C]indacaterol were investigated in healthy male subjects. Although indacaterol is administered to patients via inhalation, the dose in this study was administered orally. This was done to avoid the complications and concerns associated with the administration of a radiolabeled compound via the inhalation route. The submilligram doses administered in this study made metabolite identification and structural elucidation by mass spectrometry especially challenging. In serum, the mean t(max), C(max), and AUC(0-last) values were 1.75 h, 0.47 ng/ml, and 1.81 ng · h/ml for indacaterol and 2.5 h, 1.4 ngEq/ml, and 27.2 ngEq · h/ml for total radioactivity. Unmodified indacaterol was the most abundant drug-related compound in the serum, contributing 30% to the total radioactivity in the AUC(0-24h) pools, whereas monohydroxylated indacaterol (P26.9), the glucuronide conjugate of P26.9 (P19), and the 8-O-glucuronide conjugate of indacaterol (P37) were the most abundant metabolites, with each contributing 4 to 13%. In addition, the N-glucuronide (2-amino) conjugate (P37.7) and two metabolites (P38.2 and P39) that resulted from the cleavage about the aminoethanol group linking the hydroxyquinolinone and diethylindane moieties had a combined contribution of 12.5%. For all four subjects in the study, ≥90% of the radioactivity dose was recovered in the excreta (85% in feces and 10% in urine, mean values). In feces, unmodified indacaterol and metabolite P26.9 were the most abundant drug-related compounds (54 and 17% of the dose, respectively). In urine, unmodified indacaterol accounted for ∼0.3% of the dose, with no single metabolite accounting for >1.3%.

Pharmacological differentiation of opioid receptor antagonists by molecular and functional imaging of target occupancy and food reward-related brain activation in humans.

Opioid neurotransmission has a key role in mediating reward-related behaviours. Opioid receptor (OR) antagonists, such as naltrexone (NTX), can attenuate the behaviour-reinforcing effects of primary (food) and secondary rewards. GSK1521498 is a novel OR ligand, which behaves as an inverse agonist at the µ-OR sub-type. In a sample of healthy volunteers, we used [(11)C]-carfentanil positron emission tomography to measure the OR occupancy and functional magnetic resonance imaging (fMRI) to measure activation of brain reward centres by palatable food stimuli before and after single oral doses of GSK1521498 (range, 0.4-100 mg) or NTX (range, 2-50 mg). GSK1521498 had high affinity for human brain ORs (GSK1521498 effective concentration 50 = 7.10 ng ml(-1)) and there was a direct relationship between receptor occupancy (RO) and plasma concentrations of GSK1521498. However, for both NTX and its principal active metabolite in humans, 6-ß-NTX, this relationship was indirect. GSK1521498, but not NTX, significantly attenuated the fMRI activation of the amygdala by a palatable food stimulus. We thus have shown how the pharmacological properties of OR antagonists can be characterised directly in humans by a novel integration of molecular and functional neuroimaging techniques. GSK1521498 was differentiated from NTX in terms of its pharmacokinetics, target affinity, plasma concentration-RO relationships and pharmacodynamic effects on food reward processing in the brain. Pharmacological differentiation of these molecules suggests that they may have different therapeutic profiles for treatment of overeating and other disorders of compulsive consumption.