Targeted Inhibition of O-Linked ß-N-Acetylglucosamine Transferase as a Promising Therapeutic Strategy to Restore Chemosensitivity and Attenuate Aggressive Tumor Traits in Chemoresistant Urothelial Carcinoma of the Bladder.

Acquisition of acquired chemoresistance during treatment cycles in urothelial carcinoma of the bladder (UCB) is the major cause of death through enhancing the risk of cancer progression and metastasis. Elevated glucose flux through the abnormal upregulation of O-linked ß-N-acetylglucosamine (O-GlcNAc) transferase (OGT) controls key signaling and metabolic pathways regulating diverse cancer cell phenotypes. This study showed that OGT expression levels in two human UCB cell models with acquired resistance to gemcitabine and paclitaxel were significantly upregulated compared with those in parental cells. Reducing hyper-O-GlcNAcylation by OGT knockdown (KD) markedly facilitated chemosensitivity to the corresponding chemotherapeutics in both cells, and combination treatment with OGT-KD showed more severe growth defects in chemoresistant sublines. We subsequently verified the suppressive effects of OGT-KD monotherapy on cell migration/invasion in vitro and xenograft tumor growth in vivo in chemoresistant UCB cells. Transcriptome analysis of these cells revealed 97 upregulated genes, which were enriched in multiple oncogenic pathways. Our final choice of suspected OGT glycosylation substrate was VCAN, S1PR3, PDGFRB, and PRKCG, the knockdown of which induced cell growth defects. These findings demonstrate the vital role of dysregulated OGT activity and hyper-O-GlcNAcylation in modulating treatment failure and tumor aggression in chemoresistant UCB.

Physiologically based pharmacokinetic (PBPK) modeling of flurbiprofen in different CYP2C9 genotypes.

The aim of this study was to establish the physiologically based pharmacokinetic (PBPK) model of flurbiprofen related to CYP2C9 genetic polymorphism and describe the pharmacokinetics of flurbiprofen in different CYP2C9 genotypes. PK-Sim® software was used for the model development and validation. A total of 16 clinical pharmacokinetic data for flurbiprofen in different CYP2C9 genotypes, dose regimens, and age groups were used for the PBPK modeling. Turnover number (kcat) of CYP2C9 values were optimized to capture the observed profiles in different CYP2C9 genotypes. In the simulation, predicted fraction metabolized by CYP2C9, fraction excreted to urine, bioavailability, and volume of distribution were similar to previously reported values. Predicted plasma concentration-time profiles in different CYP2C9 genotypes were visually similar to the observed profiles. Predicted AUCinf in CYP2C9*1/*2, CYP2C9*1/*3, and CYP2C9*3/*3 genotypes were 1.44-, 2.05-, and 3.67-fold higher than the CYP2C9*1/*1 genotype. The ranges of fold errors for AUCinf, Cmax, and t1/2 were 0.84-1.00, 0.61-1.22, and 0.74-0.94 in development and 0.59-0.98, 0.52-0.97, and 0.61-1.52 in validation, respectively, which were within the acceptance criterion. Thus, the PBPK model was successfully established and described the pharmacokinetics of flurbiprofen in different CYP2C9 genotypes, dose regimens, and age groups. The present model could guide the decision-making of tailored drug administration strategy by predicting the pharmacokinetics of flurbiprofen in various clinical scenarios.

Physiologically based pharmacokinetic (PBPK) modeling for prediction of celecoxib pharmacokinetics according to CYP2C9 genetic polymorphism.

Celecoxib is a non-steroidal anti-inflammatory drug (NSAID) and a representative selective cyclooxygenase (COX)-2 inhibitor, which is commonly prescribed for osteoarthritis, rheumatoid arthritis, ankylosing spondylitis, acute pain, and primary dysmenorrhea. It is mainly metabolized by CYP2C9 and partly by CYP3A4 after oral administration. Many studies reported that CYP2C9 genetic polymorphism has significant effects on the pharmacokinetics of celecoxib and the occurrence of adverse drug reactions. The aim of this study was to develop a physiologically based pharmacokinetic (PBPK) model of celecoxib according to CYP2C9 genetic polymorphism for personalized pharmacotherapy. Initially, a clinical pharmacokinetic study was conducted where a single dose (200 mg) of celecoxib was administered to 39 healthy Korean subjects with CYP2C9*1/*1 or CYP2C9*1/*3 genotypes to obtain data for PBPK development. Based on the conducted pharmacokinetic study and a previous pharmacokinetic study involving subjects with CYP2C9*1/*13 and CYP2C9*3/*3 genotype, PBPK model for celecoxib was developed. A PBPK model for CYP2C9*1/*1 genotype group was developed and then scaled to other genotype groups (CYP2C9*1/*3, CYP2C9*1/*13 and CYP2C9*3/*3). After model development, model validation was performed with comparison of five pharmacokinetic studies. As a result, the developed PBPK model of celecoxib successfully described the pharmacokinetics of each CYP2C9 genotype group and its predicted values were within the acceptance criterion. Additionally, all the predicted values were within two-fold error range in comparison to the previous pharmacokinetic studies. This study demonstrates the possibility of determining the appropriate dosage of celecoxib for each individual through the PBPK modeling with CYP2C9 genomic information. This approach could contribute to the reduction of adverse drug reactions of celecoxib and enable precision medicine.

Physiologically based pharmacokinetic modeling of candesartan related to CYP2C9 genetic polymorphism in adult and pediatric patients.

Candesartan cilexetil is an angiotensin II receptor blocker and it is widely used to treat hypertension and heart failure. This drug is a prodrug that rapidly converts to candesartan after oral administration. Candesartan is metabolized by cytochrome P450 2C9 (CYP2C9) enzyme or uridine diphosphate glucurinosyltransferase 1A3, or excreted in an unchanged form through urine, biliary tract and feces. We investigated the effect of genetic polymorphism of CYP2C9 enzyme on drug pharmacokinetics using physiologically based pharmacokinetic (PBPK) modeling. In addition, by introducing the age and ethnicity into the model, we developed a model that can propose an appropriate dosage regimen taking into account the individual characteristics of each patient. To evaluate the suitability of the model, the results of a clinical trial on twenty-two healthy Korean subjects and their CYP2C9 genetic polymorphism data was applied. In this study, PK-Sim® was used to develop the PBPK model of candesartan.

Relationship between plasma exposure of zolpidem and CYP2D6 genotype in healthy Korean subjects.

Zolpidem, a widely prescribed hypnotic agent, is extensively metabolized by cytochrome P450 (CYP) 3A4, and CYP2C9, CYP1A2 and CYP2D6 are also involved in the metabolism of zolpidem. The aim of the study was to investigate the effects of CYP2D6 genotypes on the exposure of zolpidem. The healthy male volunteers were divided into three different genotype groups (CYP2D6*wt/*wt [*wt = *1 or *2], CYP2D6*wt/*10, and CYP2D6*10/*10). Each subject received a single oral dose of zolpidem 5 mg with or without a steady-state concentration of clarithromycin (a potent inhibitor of CYP3A4), and plasma concentrations of zolpidem were measured up to 12 h after zolpidem dosing by using liquid chromatography-tandem mass spectrometry method. When zolpidem was administered alone, the exposure of zolpidem (the total areas under the curve and the mean peak plasma concentrations) was not significantly different among three different genotype groups. Even with the steady-state concentration of clarithromycin, a potent CYP3A4 inhibitor, there were no significant differences in the exposure of zolpidem in relation to CYP2D6 genotypes.

Effects of paroxetine on the pharmacokinetics of atomoxetine and its metabolites in different CYP2D6 genotypes.

The aim of this study was to investigate the effects of paroxetine, a potent inhibitor of CYP2D6, on the pharmacokinetics of atomoxetine and its two metabolites, 4-hydroxyatomoxetine and N-desmethylatomoxetine, in different CYP2D6 genotypes. Twenty-six healthy subjects were recruited and divided into CYP2D6*wt/*wt (*wt=*1 or *2, n = 10), CYP2D6*wt/*10 (n = 9), and CYP2D6*10/*10 groups (n = 7). In atomoxetine phase, all subjects received a single oral dose of atomoxetine (20 mg). In paroxetine phase, after administration of a single oral dose of paroxetine (20 mg) for six consecutive days, all subjects received a single oral dose of atomoxetine with paroxetine. Plasma concentrations of atomoxetine and its metabolites were determined up to 24 h after dosing. During atomoxetine phase, there were significant differences in Cmax and AUC0-24 of atomoxetine and N-desmethylatomoxetine among three genotype groups, whereas significant differences were not found in relation to CYP2D6*10 allele after administration of paroxetine. AUC ratios of 4-hydroxyatomoxetine and N-desmethylatomoxetine to atomoxetine were significantly different among three genotype groups during atomoxetine phase (all, P < 0.001), but after paroxetine treatment significant differences were not found. After paroxetine treatment, AUC0-24 of atomoxetine was increased by 2.3-, 1.7-, and 1.3-fold, in CYP2D6*wt/*wt, CYP2D6*wt/*10, and CYP2D6*10/*10 groups in comparison to atomoxetine phase, respectively. AUC ratio of 4-hydroxyatomoxetine to atomoxetine in each group was significantly decreased, whereas AUC ratio of N-desmethylatomoxetine to atomoxetine significantly increased after administration of paroxetine. In conclusion, paroxetine coadministration significantly affected pharmacokinetic parameters of atomoxetine and its two metabolites, 4-hydroxyatomoxetine and N-desmethylatomoxetine. When atomoxetine was administered alone, Cmax, AUC0-24 and CL/F of atomoxetine were significantly different among the three CYP2D6 genotype groups. However, after paroxetine coadministration, no significant differences in these pharmacokinetic parameters were observed among the CYP2D6 genotype groups.

ABCB1 c.2677G>T/c.3435C>T diplotype increases the early-phase oral absorption of losartan.

Losartan has been shown to be a substrate of the drug-efflux transporter MDR1, encoded by the ABCB1 gene. ABCB1 c.2677G>T and c.3435C>T variants are known to be associated with reduced expression and function of P-glycoprotein (P-gp). We investigated the effects of ABCB1 diplotype on the pharmacokinetics of losartan. Thirty-eight healthy Korean volunteers with different ABCB1 diplotypes [c.2677G> T and c.3435C>T; carriers of GG/CC (n = 13), GT/CT (n = 12) and TT/TT (n = 13) diplotype] were recruited and administered a single 50 mg oral dose of losartan potassium. Losartan and its active metabolite E-3174 samples in plasma and urine were collected up to 10 and 8 h after drug administration, respectively, and the concentrations of both samples were determined by HPLC method. Significant differences were observed in Cmax of losartan and losartan plus E-3174 (Lo + E) among the three diplotype groups (both P < 0.01). However, the power of the performed test is less than the desired power (0.800). The tmax of losartan and E-3174 in three diplotype groups were also significantly different (both P < 0.01). The AUC values of Lo + E were significantly different among the three diplotype groups until 6 h after losartan administration (P < 0.01). On the contrary, AUC at the periods of 8-10 h and 10 h-infinity of Lo + E were significantly lower in the TT/TT group than in the GG/CC group. Urinary excretion of losartan until 4 h after losartan administration in the TT/TT group was higher than that of the GG/CC group. These results suggest that c.2677G>T/c.3435C>T diplotypes of ABCB1 may significantly increase the early-phase absorption of losartan, but not the total absorption.

Effects of CYP2D6 genetic polymorphism on the pharmacokinetics of metoclopramide.

Metoclopramide inhibits the central and peripheral D2 receptors and is frequently prescribed in adults and children as an antiemetic or a prokinetic drug to control symptoms of upper gastrointestinal motor disorders. Metoclopramide is predominantly metabolized via N-dealkylation and it is primarily mediated by CYP2D6 which is highly polymorphic. Thus, the effects of CYP2D6 genetic polymorphism on the pharmacokinetics of metoclopramide were evaluated in this study. All volunteers were genotyped for CYP2D6 and divided into four different genotype groups (CYP2D6*wt/*wt [*wt = *1 or *2], CYP2D6*wt/*10, CYP2D6*10/*10, and CYP2D6*5/*10). Each subject received a single oral dose of metoclopramide 10 mg. Plasma concentrations of metoclopramide were measured by using HPLC-UV. Compared to CYP2D6*wt/*wt, AUCinf of CYP2D6*wt/*10, CYP2D6*10/*10, and CYP2D6*5/*10 significantly increased by 1.5-, 2.3-, and 2.5-fold, respectively. Cmax also increased significantly in comparison to CYP2D6*wt/*wt across all genotype groups, with 1.5-, 1.7-, and 1.7-fold increases seen in CYP2D6*wt/*10, CYP2D6*10/*10, and CYP2D6*5/*10 groups, respectively. The CL/F of metoclopramide decreased in CYP2D6 genotype groups with decreased function alleles, as decreases of 37%, 56% and 61% were observed in CYP2D6*wt/10, *10/10, and *5/*10 genotype groups in comparison to the CYP2D6*wt/*wt group. In conclusion, the genetic polymorphisms of CYP2D6 significantly affected metoclopramide pharmacokinetics.

Effects of steady-state clarithromycin on the pharmacokinetics of zolpidem in healthy subjects.

Zolpidem is extensively metabolized by CYP3A4, CYP2C9 and CYP1A2. Previous studies demonstrated that pharmacokinetics of zolpidem was affected by CYP inhibitors, but not by short-term treatment of clarithromycin. The objective of this study was to investigate the effects of steady-state clarithromycin on the pharmacokinetics of zolpidem in healthy subjects. In the control phase, 33 subjects received a single dose of zolpidem (5 mg). One week later, in the clarithromycin phase, the subjects received clarithromycin (500 mg) twice daily for 5 days to reach steady state concentrations, followed by zolpidem (5 mg) and clarithromycin (500 mg). In each phase, plasma concentrations of zolpidem were evaluated up to 12 h after drug administration by using liquid chromatography-tandem mass spectrometry method. In the clarithromycin phase, mean total area under the curve of zolpidem (AUCinf) was 1.62-fold higher and the time to reach peak plasma concentration of zolpidem (tmax) was prolonged by 1.95-fold compared to the control phase. In addition, elimination half-life (t1/2) of zolpidem was 1.40-fold longer during co-administration with clarithromycin and its apparent oral clearance (CL/F) was 36.2% lower with clarithromycin administration. The experimental data demonstrate the significant pharmacokinetic interaction between zolpidem and clarithromycin at steady-state.

Influence of CYP2D6 genetic polymorphism on pharmacokinetics of active moiety of tolterodine.

Tolterodine is metabolized to an active 5-hydroxymethyl tolterodine (5-HMT) by CYP2D6. This study investigated the relationship between CYP2D6 genotypes and pharmacokinetics of tolterodine and its active metabolite in healthy Korean subjects. All volunteers were genotyped for CYP2D6 and divided into four different genotype groups (CYP2D6*wt/*wt [*wt = *1 or *2], CYP2D6*wt/*10, CYP2D6*10/*10, and CYP2D6*5/*10). Each subject received a single oral dose of tolterodine tartrate (2 mg) in single-dose phase of the study. After the single-dose phase of the study, the same subjects received a single oral dose of tolterodine tartrate (2 mg) once daily for 1 week during multiple-dose tolterodine administration phase. Plasma concentrations of tolterodine and 5-HMT were measured by using liquid chromatography-tandem mass spectrometry method. Our study demonstrated that plasma exposure of tolterodine in CYP2D6*10/*10 and CYP2D6*5/*10 group significantly increased, compared with CYP2D6*wt/*wt group (P < 0.001). The pharmacokinetic parameters of 5-HMT were not significantly different in relation to CYP2D6 genotype, as 5-HMT itself is also metabolized by CYP2D6. With regard to active moiety (tolterodine + 5-HMT), Cmax and AUC0-24 was significantly increased in CYP2D6*10/*10 group, compared with CYP2D6*wt/*wt group (P < 0.001). Thus, our study showed the pharmacokinetics of tolterodine and its active moiety was significantly different in relation to CYP2D6 genotype.

TinyONet: A Cache-Based Sensor Network Bridge Enabling Sensing Data Reusability and Customized Wireless Sensor Network Services.

In recent years, a few protocol bridge research projects have been announced to enable a seamless integration of Wireless Sensor Networks (WSNs) with the TCP/IP network. These studies have ensured the transparent end-to-end communication between two network sides in the node-centric manner. Researchers expect this integration will trigger the development of various application domains. However, prior research projects have not fully explored some essential features for WSNs, especially the reusability of sensing data and the data-centric communication. To resolve these issues, we suggested a new protocol bridge system named TinyONet. In TinyONet, virtual sensors play roles as virtual counterparts of physical sensors and they dynamically group to make a functional entity, Slice. Instead of direct interaction with individual physical sensors, each sensor application uses its own WSN service provided by Slices. If a new kind of service is required in TinyONet, the corresponding function can be dynamically added at runtime. Beside the data-centric communication, it also supports the node-centric communication and the synchronous access. In order to show the effectiveness of the system, we implemented TinyONet on an embedded Linux machine and evaluated it with several experimental scenarios.

The influences of CYP2C9*1/*3 genotype on the pharmacokinetics of zolpidem.

Zolpidem is predominantly metabolized by CYP3A4, and to a lesser extent by CYP2C9, CYP1A2, CYP2D6 and CYP2C19. The aim of this study was to identify the effects of CYP2C9*3 allele on the pharmacokinetics of zolpidem. Healthy male subjects were divided into two genotype groups, CYP2C9*1/*1 and CYP2C9*1/*3. They received a single oral dose of 5 mg zolpidem, and the plasma concentrations of zolpidem were determined up to 12 h after drug administration. In addition, since zolpidem is metabolized at a high rate by CYP3A4, the effect of CYP2C9*3 allele on the pharmacokinetics of zolpidem was also observed in the condition where CYP3A4 was sufficiently inhibited by the steady-state concentration of clarithromycin, a potent CYP3A4 inhibitor. For this, clarithromycin 500 mg was administered twice daily for 5 days. Plasma concentrations of zolpidem were determined using liquid chromatography-tandem mass spectrometry method. The overall pharmacokinetic parameters of zolpidem were not significantly different between two CYP2C9 genotypes. Even with the potent CYP3A4 inhibitor clarithromycin present at steady-state concentrations, there were no significant differences in the exposure of zolpidem, except for elimination half-life (t1/2). In conclusion, our study suggests that CYP2C9*1/*3 genotype does not affect the plasma exposure of zolpidem.

Effects of genetic polymorphisms of CYP2C19 on the pharmacokinetics of zolpidem.

Zolpidem is indicated for the short-term treatment of insomnia and it is predominantly metabolized by CYP3A4, and to a lesser extent by CYP2C19, CYP1A2, and CYP2C9. Therefore, we evaluated the effects of CYP2C19 genetic polymorphisms on the pharmacokinetics of zolpidem in healthy male subjects. Thirty-two male subjects were recruited and all subjects were classified into three groups according to their genotypes: CYP2C19EM (CYP2C19*1/*1, n = 12), CYP2C19IM (CYP2C19*1/*2 or *1/*3, n = 10), and CYP2C19PM (CYP2C19*2/*2, *2/*3 or *3/*3, n = 10). The pharmacokinetic parameters of zolpidem were compared in three CYP2C19 genotype groups after zolpidem administration with or without a CYP3A4 inhibitor at steady-state concentration. Plasma concentrations of zolpidem were determined up to 12 h after drug administration by liquid chromatography-tandem mass spectrometry method. The maximum plasma concentration (Cmax) differed, but mean total area under the plasma concentration-time curve (AUCinf), half-life (t1/2), and apparent oral clearance (CL/F) of zolpidem administered alone did not significantly differ among the three different CYP2C19 genotype groups. Furthermore, when zolpidem was administered with a CYP3A4 inhibitor at steady-state concentration, there were no significant differences in any of the pharmacokinetic parameters of zolpidem in relation to CYP2C19 genotypes. In conclusion, we did not find any evidence for the impact of CYP2C19 genetic polymorphisms on the pharmacokinetic parameters of zolpidem.

CYP2D6 allele frequencies in Korean population, comparison with East Asian, Caucasian and African populations, and the comparison of metabolic activity of CYP2D6 genotypes.

Cytochrome P450 (CYP) 2D6 is present in less than about 2% of all CYP enzymes in the liver, but it is involved in the metabolism of about 25% of currently used drugs. CYP2D6 is the most polymorphic among the CYP enzymes. We determined alleles and genotypes of CYP2D6 in 3417 Koreans, compared the frequencies of CYP2D6 alleles with other populations, and observed the differences in pharmacokinetics of metoprolol, a prototype CYP2D6 substrate, depending on CYP2D6 genotype. A total of 3417 unrelated healthy subjects were recruited for the genotyping of CYP2D6 gene. Among them, 42 subjects with different CYP2D6 genotypes were enrolled in the pharmacokinetic study of metoprolol. The functional allele *1 and *2 were present in frequencies of 34.6 and 11.8%, respectively. In decreased functional alleles, *10 was the most frequent with 46.2% and *41 allele was present in 1.4%. The nonfunctional alleles *5 and *14 were present at 4.5 and 0.5% frequency, respectively. The *X × N allele was present at a frequency of 1.0%. CYP2D6*1/*1, *1/*2 and *2/*2 genotypes with normal enzyme activity were present in 12.1%, 8.6% and 1.4% of the subjects, respectively. CYP2D6*5/*5, *5/*14, and *14/*14 genotypes classified as poor metabolizer were only present in 4, 2, and 1 subjects, respectively. Mutant genotypes with frequencies of more than 1% were CYP2D6*1/*10 (32.0%), *10/*10 (22.3%), *2/*10 (11.7%), *5/*10 (3.7%), *1/*5 (2.5%), and *10/*41 (1.2%). The relative clearance of metoprolol in CYP2D6*1/*10, *1/*5, *10/*10, *5/*10, and *5/*5 genotypes were 69%, 57%, 24%, 14% and 9% of CYP2D6*wt/*wt genotype, respectively. These results will be very useful in establishing a strategy for precision medicine related to the genetic polymorphism of CYP2D6.

Effect of the CYP2D6*10 allele on the pharmacokinetics of clomiphene and its active metabolites.

Clomiphene citrate, a selective estrogen receptor modulator, is metabolized into its 4-hydroxylated active metabolites, primarily by CYP2D6. In this study, we investigated the effects of the most common CYP2D6 variant allele in Asians, CYP2D6*10, on the pharmacokinetics of clomiphene and its two active metabolites (4-OH-CLO and 4-OH-DE-CLO) in healthy Korean subjects. A single 50-mg oral dose of clomiphene citrate was given to 22 Korean subjects divided into three genotype groups according to CYP2D6 genotypes, CYP2D6*wt/*wt (n = 8; *wt = *1 or *2), CYP2D6*wt/*10 (n = 8) and CYP2D6*10/*10 (n = 6). Concentrations of clomiphene and its metabolites were determined using a validated HPLC-MS/MS analytical method in plasma samples collected up to 168 h after the drug intake. There was a significant difference only in the Cmax of clomiphene between three CYP2D6 genotype groups (p < 0.05). Paradoxically, the elimination half-life (t1/2) and AUC of both active metabolites were all significantly increased in the CYP2D6*10 homozygous carriers, compared with other genotype groups (all p < 0.001). The AUCinf of corrected clomiphene active moiety in CYP2D6*10/*10 subjects was 2.95- and 2.05-fold higher than that of CYP2D6*wt/*wt and *wt/*10 genotype groups, respectively (both p < 0.001). Along with the partial impacts on the biotransformation of clomiphene and its metabolites by CYP2D6 genetic polymorphism, further studies on the effects of other CYP enzymes in a multiple-dosing condition can provide more definite evidence for the inter-individual variabilities in clomiphene pharmacokinetics and/or drug response.

Simultaneous determination of tolterodine and its two metabolites, 5-hydroxymethyltolterodine and N-dealkyltolterodine in human plasma using LC-MS/MS and its application to a pharmacokinetic study.

Tolterodine is a nonselective muscarinic antagonist that is indicated for the overactive urinary bladder and other urinary difficulties. We developed and validated a simple, rapid and sensitive high-performance liquid chromatography analytical method utilizing tandem mass spectrometry (LC-MS/MS) for the quantitation of tolterodine and its major metabolites, 5-hydroxymethyltolterodine (5-HMT) and N-dealkyltolterodine (NDT), in human plasma. After liquid-liquid extraction with methyl t-butyl ether, chromatographic separation of the three analytes was achieved using a reversed-phase Luna Phenyl-hexyl column (100 × 2.0 mm, 3 µm particles) with a mobile phase of 10 mM ammonium formate buffer (pH 3.5)-methanol (10:90, v/v) and quantified by MS/MS detection in electrospray ionization (ESI) positive ion mode. The retention time of tolterodine, 5-HMT, NDT, and internal standard (IS) were 1.4, 1.24, 1.33, and 1.26 min, respectively. The calibration curves were linear over a range of 0.025-10 ng/ml for tolterodine and 5-HMT, and 0.05-10 ng/ml for NDT. The lower limit of quantifications using 200 µl of human plasma was 0.025 ng/ml for tolterodine and 5-HMT, and 0.05 ng/ml for NDT. The mean accuracy and precision for intra- and inter-run validation of tolterodine, 5-HMT, and NDT were all within acceptable limits. These results showed that a simple, rapid and sensitive LC-MS/MS method for the quantification of tolterodine and its major metabolites in human plasma was developed. This method was successfully applied to a pharmacokinetic study in humans.