"Natural Amphetamine" Khat: A Cultural Tradition or a Drug of Abuse?

Khat, Catha edulis Forsk, is among the most widely used plant-based psychoactive substance in the world. Grown in Eastern Africa, Horn of Africa, and southwestern part of the Arabian Peninsula, its fresh young leaves and twigs are used daily by over 20 million people for the psychostimulatory effects it produces in the user, a practice deeply rooted in the history, tradition, and culture of the indigenous population. Once hardly known outside the regions where it is grown and used, khat use has now spread to other countries. This review will cover the, phytochemistry, pharmacokinetics of the active ingredients-cathinone, cathine, norephedrine, neurochemistry, effects on cognitive and executive functions as well as its ability to produce dependency in the user. Whether it is an innocuous cultural practice or a drug of abuse is debatable as the preclinical and clinical data needed to arrive at an authoritative conclusion is lacking.

Simultaneous quantification and pharmacokinetics of alkaloids in Herba Ephedrae-Radix Aconiti Lateralis extracts.

The combination of Herba Ephedrae (Mahuang in Chinese) and Radix Aconiti Lateralis (Fuzi in Chinese) is a classical preparation in traditional Chinese medicine and used for treating colds and rheumatic arthralgia. However, herbal medicines containing ephedrines and Aconitum alkaloids are strictly regulated because of the potential for adverse effects on the cardiovascular system and the central nervous system. We aimed to investigate the pharmacokinetics of 11 alkaloids in the Mahuang-Fuzi combination and single-herb extracts after oral administration in rats. The alkaloids were norephedrine, norpseudoephedrine, ephedrine, pseudoephedrine, methylephedrine, aconitine, mesaconitine, hypaconitine, benzoylaconine, benzoylmesaconine and benzoylhypaconine. Simultaneous determination of the alkaloids, including two pairs of diastereomers, was achieved in 14.5 min by a simple, rapid and sensitive ultra-performance liquid chromatography-tandem mass spectrometry method. The separation was performed on a Zorbax SB-Aq column (100 mm × 2.1 mm, 3.5 µm) at a flow rate of 0.3 mL/min using acetonitrile-0.1% formic acid aqueous solution as the mobile phase. The validated method demonstrated adequate sensitivity, selectivity and process efficiency for the quantitative analysis of complex herbal components. Compared with single-herb extracts, alkaloids in plasma (except methylephedrine, benzoylmesaconine and benzoylhypaconine) showed slower elimination (the mean residence time or half-life was longer), although the maximum plasma concentration and area under the plasma concentration curve values decreased. Accumulation may occur with continuous drug intake. These results suggest that drug monitoring may be essential for the safe use of the Mahuang-Fuzi combination.

Tolterodine extended release in the treatment of male OAB/storage LUTS: a systematic review.

BACKGROUND: Overactive bladder (OAB)/ storage lower urinary tract symptoms (LUTS) have a high prevalence affecting up to 90% of men over 80 years. The role of sufficient therapies appears crucial. In the present review, we analyzed the mechanism of action of tolterodine extended-release (ER) with the aim to clarify its efficacy and safety profile, as compared to other active treatments of OAB/storage LUTS. METHODS: A wide Medline search was performed including the combination of following words: "LUTS", "BPH", "OAB", "antimuscarinic", "tolterodine", "tolterodine ER". IPSS, IPSS storage sub-score and IPSS QoL (International Prostate Symptom Score) were the validated efficacy outcomes. In addition, the numbers of urgency episodes/24 h, urgency incontinence episodes/24 h, incontinence episodes/24 h and pad use were considered. We also evaluated the most common adverse events (AEs) reported for tolterodine ER. RESULTS: Of 128 retrieved articles, 109 were excluded. The efficacy and tolerability of tolterodine ER Vs. tolterodine IR have been evaluated in a multicenter, double-blind, randomized placebo controlled study in 1529 patients with OAB. A 71% mean reduction in urgency incontinence episodes was found in the tolterodine ER group compared to a 60% reduction in the tolterodine IR (p < 0.05). Few studies evaluated the clinical efficacy of α-blocker/tolterodine combination therapy. In patients with large prostates (prostate volume >29 cc) only the combination therapy significantly reduced 24-h voiding frequency (2.8 vs. 1.7 with tamsulosin, 1.4 with tolterodine, or 1.6 with placebo). A recent meta-analysis evaluating tolterodine in comparison with other antimuscarinic drugs demonstrated that tolterodine ER was significantly more effective than placebo in reducing micturition/24 h, urinary leakage episodes/24 h, urgency episodes/24 h, and urgency incontinence episodes/24 h. With regard to adverse events, tolterodine ER was associated with a good adverse event profile resulting in the third most favorable antimuscarinic. Antimuscarinic drugs are the mainstay of pharmacological therapy for OAB / storage LUTS; several studies have demonstrated that tolterodine ER is an effective and well tolerated formulation of this class of treatment. CONCLUSION: Tolterodine ER resulted effective in reducing frequency urgency and nocturia and urinary leakage in male patients with OAB/storage LUTS. Dry mouth and constipation are the most frequently reported adverse events.

Design of transparent film-forming hydrogels of tolterodine and their effects on stratum corneum.

A transparent film-forming hydrogel formulation for tolterodine was developed using ternary phase diagram and Box-Behnken design (BBD). Carbopol 980 (neutralized by triethanolamine), hydroxypropyl cellulose (HPC), hydroxypropyl methyl cellulose (HPMC) and Tween 80 were used as matrices. Solvent was the mixture of water and ethyl alcohol. The measured 24 h cumulative drug release rate (86.02%) was consistent with the predicted value (85.42%) in mice. Steady-state flux (J) of tolterodine in optimized formulation across rat full skin, epidermal, dermis and subcutaneous tissue were 15.83, 18.55, 37.15 and 81.82 µg cm(-2) h(-1), respectively. Fourier transform infrared spectroscopy (FTIR) and differential scanning calorimetry (DSC) results suggested that the hydrogels could impact lipid status in SC, which was consistent with Ea (8.638 kcal/mol) of tolterodine from optimized formulation in rats. In the pharmacokinetic studies, sustained-release over 24 h and absolute bioavailability of the hydrogels (24.53%) was higher than tolterodine tablets (15.16%) in rats. The hydrogels were suitable for systemic administration of tolterodine for the treatment of overactive bladder.

Drug development for pediatric neurogenic bladder dysfunction: dosing, endpoints, and study design.

Pediatric drug development is challenging when a product is studied for a pediatric disease that has a different underlying etiology and pathophysiology compared to the adult disease. Neurogenic bladder dysfunction (NBD) is such a therapeutic area with multiple unsuccessful development programs. The objective of this study was to critically evaluate clinical trial design elements that may have contributed to unsuccessful drug development programs for pediatric NBD. Trial design elements of drugs tested for pediatric NBD were identified from trials submitted to the U.S. Food and Drug Administration. Data were extracted from publically available FDA reviews and labeling and included trial design, primary endpoints, enrollment eligibilities, and pharmacokinetic data. A total of four products were identified. Although all four programs potentially provided clinically useful information, only one drug (oxybutynin) demonstrated efficacy in children with NBD. The lack of demonstrable efficacy for the remainder of the products illustrates that future trials should give careful attention to testing a range of doses, using objectively measured, clinically meaningful endpoints, and selecting clinical trial designs that are both interpretable and feasible. Compiling the drug development experience with pediatric NBD will facilitate an improved approach for future drug development for this, and perhaps other, therapeutic areas.

Preparation and evaluation of once-daily sustained-release coated tablets of tolterodine-L-tartrate.

In this study, once-daily, sustained-release matrix tablets of tolterodine l-tartrate (TOL) for treatment of overactive bladder (OAB) were prepared by direct compression using various amounts of hydrophilic polymers such as HPMC 2910 and HPMC 2208 along with other tablet excipients; the tablets were then coated. In vitro dissolution studies were carried out under different pH conditions. The dissolution data were fitted into zero-order, first-order, Higuchi and Korsemeyer-Peppas models to identify the pharmacokinetics and mechanism of drug release. Among the four formulations (F1-F4), the dissolution profiles of formulation F2 were most similar to the marketed product with similarity and difference factors of 70.25 and 1.59 respectively. Furthermore, pharmacokinetic studies were carried out in healthy human volunteers after oral administration of the prepared TOL sustained-release matrix-coated tablet and the marketed product. The results revealed that the pharmacokinetic parameters of AUC, Cmax, Tmax, t1/2, Kel, and MRT of TOL for the developed formulation (F2) were not significantly different from that for the marketed product, suggesting that they were bioequivalent. Therefore, the developed sustained-release tablet formulation of TOL could be an alternative dosage form to the SR capsule for treatment of OAB.

Therapeutic benefit in patients switching tolterodine to other novel antimuscarinic agents.

OBJECTIVES: To explore in the daily clinical practice setting that antimuscarinic, Fesoterodine or Solifenacin, provides a greater clinical benefit after changing their prior Overactive Bladder (OAB) therapy with tolterodine extended-release (ER) to other novel antimuscarinic agents. MATERIAL AND METHODS: A post-hoc analysis of data from an observational multicenter, cross-sectional, retrospective study. Adult patients of both sexes, with OAB and OAB-V8 score≥8, who switched to fesoterodine or solifenacin within the 3-4 months before study visit from their prior tolterodine-ER-based therapy due to poor response were included. 92 patients were selected for each treatment group, matched (1:1) according to conditioned probability using the propensity score. Benefit of treatment change perceived by the physician and patient was evaluated by means of the Clinical Global Impression of Improvement subscale (CGI-I) and Treatment Benefit Scale (TBS), respectively. Degree of worry, bother and interference with daily living activities due to urinary symptoms, level of satisfaction, and preference for current treatment were also assessed. RESULTS: Fesoterodine provided a significantly greater improvement than solifenacina in terms of therapeutic benefit perceived by the physician according to ICG-I. 96.7% of the patients on fesoterodine treatment vs. 81.6% of the solifenacin group showed a score of improvement in TBS (P<.05). Fesoterodine was also better rated than solifenacin with regard to satisfaction and preference for the new treatment (93.4 vs. 78.2% P<.05). CONCLUSIONS: In daily clinical practice the switch from tolterodine LP to fesoterodine seems to provide greater benefits both from the physician's and the patient's point of view compared with those provided by solifenacin.

Preparation, characterization and pharmacological evaluation of tolterodine hydrogels for the treatment of overactive bladder.

In this study, transdermal gel formulations for tolterodine were developed to investigate the effects of gel matrix and chemical enhancers on drug skin permeation from tolterodine hydrogels. In vitro permeation studies of tolterodine through excised mouse skin were carried out using Franz-type diffusion cells. In the optimum gel formulation, Carbopol 940 was selected as the gel matrix. Compared to gels without enhancer, tolterodine hydrogels with N-methyl pyrrolidone (NMP) showed significant enhancing effect on transdermal permeation of tolterodine (p<0.05). The results of in vitro percutaneous delivery experiment showed that the relationship of the steady accumulative percutaneous amount (Q, µg cm(-2)) of tolterodine hydrogels and time was Q4-12h=770.19t(1/2)-966.99. Tolterodine permeated at the steady-state speed of 770.19 µg cm(-2)h(-1) and its release coincided with Higuchi Equation. The pharmacokinetic properties of the optimized tolterodine formulation were studied in rabbits. The absolute bioavailability of tolterodine was 11.47%. Since the absence of hepatic first-pass metabolism, only a single active compound-tolterodine was detected in the plasma. A skin irritation study was also carried out on rabbits, and the results showed tolterodine hydrogels had no skin irritation. In the pharmacodynamic study, the significant effects of tolterodine hydrogels on the inhibition of pilocarpine-induced rat urinary bladder contraction were last to 12h, indicating that tolterodine hydrogels could produce prolonged pharmacological responses. In conclusion, tolterodine hydrogels were formulated successfully using Carbopol 940 and NMP and these results helped in finding the optimum formulation for percutaneous drug release. It is quite evident that tolterodine hydrogels may offer a possibility to avoid the first-pass effect, resulting in a single active compound of tolterodine in plasma, which may profit on the patient under the dose control and the reduction of potential adverse effect from two active compounds in the body.

Synergistic effect of iontophoresis and chemical enhancers on transdermal permeation of tolterodine tartrate for the treatment of overactive bladder.

PURPOSE: The objective of the study was to evaluate the synergistic transdermal permeation effect of chemical enhancers and iontophoresis technique on tolterodine tartrate (TT) transdermal gel and to evaluate its pharmacokinetic properties. MATERIALS AND METHODS: Taguchi robust design was used for optimization of formulations. Skin permeation rates were evaluated using the Keshary-chein type diffusion cells in order to optimize the gel formulation. In-vivo studies of the optimized formulation were performed in a rabbit model and histopathology studies of optimized formulation were performed on rats. RESULTS: Transdermal gels were formulated successfully using Taguchi robust design method. The type of penetration enhancer, concentration of penetration enhancer, current density and pulse on/off ratio were chosen as independent variables. Type of penetration enhancer was found to be the significant factor for all the responses. Permeation parameters were evaluated when maximum cumulative amount permeated in 24 hours (Q24) was 145.71 ± 2.00µg/cm² by CIT4 formulation over control (91.89 ± 2.30µg/cm²). Permeation was enhanced by 1.75 fold by CIT4 formulation. Formulation CIT4 containing nerolidol (5%) and iontophoretic variables applied (0.5mA/cm² and pulse on/off ratio 3:1) was optimized. In vivo studies with optimized formulation CIT4 showed increase in AUC and T1/2 when compared to oral suspension in rabbits. The histological studies showed changes in dermis indicating the effect of penetration enhancers and as iontophoresis was continued only for two cycles in periodic fashion so it did not cause any skin damage observed in the slides. CONCLUSION: Results indicated that iontophoresis in combination with chemical enhancers is an effective method for transdermal administration of TT in the treatment of overactive bladder.

Effect of HNF4α genetic polymorphism G60D on the pharmacokinetics of CYP2D6 substrate tolterodine in healthy Korean individuals.

Hepatocyte nuclear receptor 4α (HNF4α) plays a central role in regulating human drug-metabolizing enzymes. Our previous study suggested that the newly identified polymorphism G60D in the HNF4α gene may decrease its downstream CYP2D6 activity in Asians. To confirm this effect in a clinical setting, we carried out a full pharmacokinetic study of a single oral dose of CYP2D6 substrate tolterodine in 30 healthy Korean individuals (HNF4α wild type: n = 24; HNF4α G60D heterozygotes: n = 6) who were pregenotyped for CYP2D6. Our study showed HNF4α G60D to be an independent predictor for increased AUC0-∞, C max of tolterodine and increased AUC0-∞ of the active moiety (tolterodine+5-hydroxymethyl-tolterodine) (P<0.05). A significant proportion of the variance in these parameters (R = 0.81, 0.59, and 0.63, respectively; P<0.01) was explained together by CYP2D6 and HNF4α genotypes. Further investigation of HNF4α genetic polymorphisms may improve the predictability of CYP2D6 activity in different populations.

Synergistic effect of iontophoresis and chemical enhancers on transdermal permeation of tolterodine tartrate for the treatment of overactive bladder

Purpose The objective of the study was to evaluate the synergistic transdermal permeation effect of chemical enhancers and iontophoresis technique on tolterodine tartrate (TT) transdermal gel and to evaluate its pharmacokinetic properties. Materials and Methods Taguchi robust design was used for optimization of formulations. Skin permeation rates were evaluated using the Keshary-chein type diffusion cells in order to optimize the gel formulation. In-vivo studies of the optimized formulation were performed in a rabbit model and histopathology studies of optimized formulation were performed on rats. Results Transdermal gels were formulated successfully using Taguchi robust design method. The type of penetration enhancer, concentration of penetration enhancer, current density and pulse on/off ratio were chosen as independent variables. Type of penetration enhancer was found to be the significant factor for all the responses. Permeation parameters were evaluated when maximum cumulative amount permeated in 24 hours (Q24) was 145.71 ± 2.00µg/cm2 by CIT4 formulation over control (91.89 ± 2.30µg/cm2). Permeation was enhanced by 1.75 fold by CIT4 formulation. Formulation CIT4 containing nerolidol (5%) and iontophoretic variables applied (0.5mA/cm2 and pulse on/off ratio 3:1) was optimized. In vivo studies with optimized formulation CIT4 showed increase in AUC and T1/2 when compared to oral suspension in rabbits. The histological studies showed changes in dermis indicating the effect of penetration enhancers and as iontophoresis was continued only for two cycles in periodic fashion so it did not cause any skin damage observed in the slides. Conclusion Results indicated that iontophoresis in combination with chemical enhancers is an effective method for transdermal administration of TT in the treatment of overactive bladder. .

A formulation approach for development of HPMC-based sustained release tablets for tolterodine tartrate with a low release variation.

OBJECTIVE: The purpose of this study was to develop hydroxypropylmethylcellulose (HPMC)-based sustained release (SR) tablets for tolterodine tartrate with a low drug release variation. METHODS: The SR tablets were prepared by formulating a combination of different grades of HPMC as the gelling agents. The comparative dissolution study for the HPMC-based SR tablet as a test and Detrusitol SR capsule as a reference was carried out, and the bioequivalence study of the two products was also conducted in human volunteers. RESULTS: The amount of HPMC, the grade of HPMC and the combination ratio of different grades of HPMC had remarkable effects on drug release from the SR tablets. Both the test and reference products had no significant difference in terms of comparative dissolution patterns in four different media (f2 > 50). Furthermore, the dissolution method and rotation speed showed no effects on the drug release from the two products. The 90% confidence intervals of the AUC(0-36) and C(max) ratios for the test and reference products were within the acceptable bioequivalence intervals of log0.8-log1.25. CONCLUSIONS: A HPMC-based SR tablet for tolterodine tartrate with a low release variation was successfully developed, which was bioequivalent to Detrusitol® SR capsule.

Saliva versus plasma pharmacokinetics: theory and application of a salivary excretion classification system.

The aims of this work were to study pharmacokinetics of randomly selected drugs in plasma and saliva samples in healthy human volunteers, and to introduce a Salivary Excretion Classification System. Saliva and plasma samples were collected for 3-5 half-life values of sitagliptin, cinacalcet, metformin, montelukast, tolterodine, hydrochlorothiazide (HCT), lornoxicam, azithromycin, diacerhein, rosuvastatin, cloxacillin, losartan and tamsulosin after oral dosing. Saliva and plasma pharmacokinetic parameters were calculated by noncompartmental analysis using the Kinetica program. Effective intestinal permeability (Peff) values were estimated by the Nelder-Mead algorithm of the Parameter Estimation module using the SimCYP program. Peff values were optimized to predict the actual average plasma profile of each drug. All other physicochemical factors were kept constant during the minimization processes. Sitagliptin, cinacalcet, metformin, tolterodine, HCT, azithromycin, rosuvastatin and cloxacillin had salivary excretion with correlation coefficients of 0.59-0.99 between saliva and plasma concentrations. On the other hand, montelukast, lornoxicam, diacerhein, losartan and tamsulosin showed no salivary excretion. Estimated Peff ranged 0.16-44.16 × 10(-4) cm/s, while reported fraction unbound to plasma proteins (fu) ranged 0.01-0.99 for the drugs under investigation. Saliva/plasma concentrations ratios ranged 0.11-13.4, in agreement with drug protein binding and permeability. A Salivary Excretion Classification System (SECS) was suggested based on drug high (H)/low (L) permeability and high (H)/low (L) fraction unbound to plasma proteins, which classifies drugs into 4 classes. Drugs that fall into class I (H/H), II (L/H) or III (H/L) are subjected to salivary excretion, while those falling into class IV (L/L) are not. Additional data from literature was also analyzed, and all results were in agreement with the suggested SECS. Moreover, a polynomial relationship with correlation coefficient of 0.99 is obtained between S* and C*, where S* and C* are saliva and concentration dimensionless numbers respectively. The proposed Salivary Excretion Classification System (SECS) can be used as a guide for drug salivary excretion. Future work is planned to test these initial findings, and demonstrate SECS robustness across a range of carefully selected (based on physicochemical properties) drugs that fall into classes I, II or III.

Inter-individual variability of in vivo CYP2D6 activity in different genotypes.

Cytochrome P450 2D6 (CYP2D6), which has a large number of genetic polymorphisms, is involved in the metabolism of a wide range of substrates. Dextromethorphan (DM) is a well-known probe drug for CYP2D6 and metabolic ratio (MR) is often used to measure the enzyme activity in vivo. Using the literature values of DM MR, we estimated the inter-individual variability of CYP2D6 hepatic intrinsic clearance (CL(int,h,2D6)) in each genotype by Monte Carlo simulation and found that the homozygote of CYP2D6*1 and the heterozygote of CYP2D6*1 and null alleles had a coefficient of variation (CV) of 43% and 56%, respectively. The variability of homozygotes of CYP2D6*2 and CYP2D6*10 was 63% and 66%, while that of the heterozygotes of CYP2D6*2 and null alleles and CYP2D6*10 and null alleles was 125% and 109%, respectively. Based on the variability and reported frequency of the CYP2D6 genotype in Asians and Caucasians, the inter-individual variability of CL(int,h,2D6) of extensive metabolizers was estimated at 60-70%, which provided comparable variability of AUC with the literature values of DM, tolterodine, risperidone and atomoxetine. It is suggested that the produced inter-individual variability of CL(int,h,2D6) in each genotype is useful for estimating AUC variability of the CYP2D6 substrates in the regional population.

Silicone adhesive, a better matrix for tolterodine patches-a research based on in vitro/in vivo studies.

OBJECTIVE: To design and optimize a drug-in-adhesive (DIA) type transdermal patch for tolterodine (TOL) based on acrylic and silicone matrixes. METHODS: Initial in vitro studies were conducted to optimize the formulations. Two types of adhesive matrixes, drug loading, and enhancers were evaluated on the TOL transport across rabbit skin. For in vivo studies, patches were administered to rabbit abdominal skin. Pharmacokinetic assessments were performed based on plasma level of TOL up to 28 h for acrylic patch and 52 h for silicone patch after topical application. RESULTS: The final formulation of acrylic adhesive type patch consisted of 10% TOL (w/w) and 5.8 × 10(-4) mol isopropyl myristate (IPM) and 2.9 × 10(-4) mol Span 80 in per unit gram (mol/g) of adhesive, while 2.5% TOL (w/w) and 2.9 × 10(-4) mol/g IPM for silicone adhesive type patch. Comparison of the pharmacokinetic parameters between two types of patches showed that the steady-state concentration of silicone type patch was 2-fold higher than that of acrylic type patch being 0.97 mg/L versus 0.49 mg/L, and the absolute bioavailability was 27.5% for silicone type patch and 6.3% for acrylic type patch, respectively. In addition, the prediction of in vivo drug level from the in vitro permeation data of silicone adhesive formulation was in good agreement with actual observed concentration data in rabbits. CONCLUSION: These results indicate that the silicone type of TOL patch is an appropriate delivery system for the treatment of overactive bladder (OAB).

Comparison of pharmacokinetic variability of fesoterodine vs. tolterodine extended release in cytochrome P450 2D6 extensive and poor metabolizers.

WHAT IS ALREADY KNOWN ABOUT THIS SUBJECT: Tolterodine and 5-hydroxymethyl tolterodine (5-HMT) are equipotent active moieties of tolterodine; 5-HMT is the singular active moiety of fesoterodine. The formation of 5-HMT from tolterodine occurs via CYP2D6, and some subjects are poor metabolizers CYP2D6. On the other hand, the formation of 5-HMT from fesoterodine occurs via ubiquitous esterases. Cross-study comparisons of data from phase 1 studies suggest that active moiety exposures are considerably more variable following tolterodine extended release vs. fesoterodine. WHAT THIS STUDY ADDS: This head-to-head study confirmed the findings of reduced pharmacokinetic variability of fesoterodine and further delineates that tolterodine, and not 5-HMT, was the principal source of variability after administration of tolterodine extended release. The data suggest that fesoterodine delivers 5-HMT consistently, regardless of CYP2D6 status, with up to 40% higher bioavailability compared with tolterodine. AIMS: Tolterodine and 5-hydroxymethyl tolterodine (5-HMT) are equipotent active moieties of tolterodine; 5-HMT is the singular active moiety of fesoterodine. Formation of 5-HMT from fesoterodine and tolterodine occurs via esterases and CYP2D6 respectively. This randomized, crossover, open-label, multiple-dose study in CYP2D6 extensive metabolizers (EMs) and poor metabolizers (PMs) compared the pharmacokinetics of fesoterodine vs. tolterodine extended release (ER). METHODS: Subjects received fesoterodine and tolterodine ER with a ≥3-day washout period. Treatment comprised 4-mg once daily doses for 5 days escalated to 8-mg once daily for 5 days. Pharmacokinetics of active moieties were compared by drug, dose and genotype. RESULTS: Active moiety exposures following fesoterodine and tolterodine ER increased proportional to dose in EMs and PMs. In EMs only, coefficients of variation for AUC and C(max) following fesoterodine (up to 46% and 48% respectively) were lower than those following tolterodine ER (up to 87% and 87% respectively). Following fesoterodine and tolterodine ER administration, active moiety exposures ranged up to sevenfold and 40-fold respectively. Mean urinary excretion of 5-HMT following fesoterodine 4 and 8 mg, respectively, was 0.44 and 0.89 mg in EMs and 0.60 and 1.32 mg in PMs. Following tolterodine ER 4 and 8 mg, it was 0.38 and 0.71 mg respectively (EMs only). Renal clearance was similar regardless of administered drug, dose or genotype. CONCLUSIONS: Tolterodine, not 5-HMT, was the principal source of variability after tolterodine ER administration. Fesoterodine delivers 5-HMT with less variability than tolterodine, regardless of CYP2D6 status, with up to 40% higher bioavailability. The pharmacokinetics of fesoterodine were considerably less variable than TER.

A comprehensive non-clinical evaluation of the CNS penetration potential of antimuscarinic agents for the treatment of overactive bladder.

WHAT IS ALREADY KNOWN ABOUT THIS SUBJECT: This study provides antimuscarinic agents for overactive bladder (OAB) display variable association with side effects mediated by the central nervous system (CNS), which may be of particular concern in the elderly. Adverse effects on CNS functioning are related to muscarinic receptor subtype selectivity and the ability of the agent to cross the blood-brain barrier, where P-gp plays a role in limiting permeability. WHAT THIS STUDY ADDS: This study provides a parallel investigation of CNS penetration of antimuscarinic OAB agents in vivo and assessment of physical properties and permeability in cell monolayers in vitro. It adds further understanding of the roles of passive transcellular permeability and P-gp in determining CNS penetration of antimuscarinic OAB agents. It also enables a comparison of CNS side-effect profiles of OAB agents with preclinical CNS penetration data. AIMS: To assess and compare the mechanisms of central nervous system (CNS) penetration of antimuscarinic overactive bladder (OAB) agents. METHODS: Physical properties were computed or compiled from the literature. Rats were administered 5-hydroxymethyl tolterodine (HMT), darifenacin, oxybutynin, solifenacin, tolterodine or trospium subcutaneously. At 1 h postdose, plasma, brain and cerebrospinal fluid (CSF) concentrations were determined using LC-MS/MS assays. Brain and plasma protein binding were determined in vitro. Permeability in the presence and absence of the efflux transporter P-glycoprotein (P-gp) was assessed in RRCK and MDCK-MDR1 transwell assays. RESULTS: Oxybutynin displayed extensive CNS penetration, with brain:plasma ratios (B:P), unbound brain:unbound plasma ratios (Kp,free) and CSF:free plasma ratios each >1. Tolterodine (B:P = 2.95, Kp,free = 0.23 and CSF:free plasma = 0.16) and solifenacin (B:P = 3.04, Kp,free = 0.28 and CSF:free plasma = 1.41) showed significant CNS penetration but with some restriction from CNS as indicated by Kp,free values significantly <1. 5-HMT, darifenacin and trospium displayed much lower B:P (0.03-0.16), Kp,free (0.01-0.04) and CSF:free plasma (0.004-0.06), consistent with poor CNS penetration. Permeability in RRCK cells was low for trospium (0.63 × 10(-6) cm s(-1) ), moderate for 5-HMT (11.7 × 10(-6) cm s(-1) ) and high for darifenacin, solifenacin, tolterodine and oxybutynin (21.5-38.2 × 10(-6) cm s(-1) ). In MDCK-MDR1 cells 5-HMT, darifenacin and trospium, were P-gp substrates, whereas oxybutynin, solifenacin and tolterodine were not P-gp substrates. CONCLUSIONS: Brain penetration was low for antimuscarinics that are P-gp substrates (5-HMT, darifenacin and trospium), and significant for those that are not P-gp substrates (oxybutynin, solifenacin and tolterodine). CNS adverse events reported in randomized controlled clinical trials show general alignment with the preclinical data described in this study.

Pharmacokinetics of tolterodine in Japanese and Koreans: physiological and stochastic assessment of ethnic differences.

Tolterodine is known as a drug which exhibits ethnic differences in pharmacokinetics between Japanese and Koreans despite genetic similarities among the populations of East Asian countries. Tolterodine is mainly metabolized by CYP2D6 to a 5-hydroxymethyl metabolite (5-HM), and 5-HM is also metabolized by CYP2D6. The reduced-function allele CYP2D6*10 is frequently observed in Asian populations. We investigated differences in the pharmacokinetics of tolterodine between small Japanese and Korean study populations by physiological and stochastic approaches with consideration of the CYP2D6 genotype. The genotype frequencies of CYP2D6*10/*10 and CYP2D6*5/*10 were found to be higher in Koreans than in Japanese, which suggested that this frequency difference occurred incidentally. The effects of CYP2D6 genotype and ethnicity on the intrinsic clearance of tolterodine by CYP2D6 were tested and only genotype was found to be a significant factor by ANCOVA. A simulation was conducted to confirm whether the observed differences in tolterodine exposure could be explained by the differences in genotype frequency found in this study. It was confirmed that the variability of intrinsic clearance could be responsible for the incidental exposure differences. In conclusion, apparent differences in exposure were found between small Japanese and Korean study populations because of the variability of intrinsic clearances and genotype frequencies.

Studies on the preparation, characterization and pharmacological evaluation of tolterodine PLGA microspheres.

In this study, poly(d,l-lactide-co-glycolide) (PLGA) microspheres of tolterodine depot formulation were prepared using oil in water (o/w) method to investigate their potential pharmacokinetic and pharmacodynamic advantages over tolterodine l-tartrate tablets. Morphological studies of the microspheres showed a spherical shape and smooth surface with mean size of 50.69-83.01 microm, and the encapsulation efficiency was improved from 62.55 to 79.10% when the polymer concentration increased from 180 to 230 mg/ml. The addition of stearic or palmitic acids could significantly raise the drug entrapment efficiency but only slightly affected the in vitro release. A low initial burst followed by a proximately constant release of tolterodine was noticed in the in vitro release profiles. The in vivo study was carried out by intramuscular (i.m.) administration of tolterodine-loaded microspheres on beagle dogs, and a sustained release of drug from the PLGA microspheres was achieved until the 18th day with a low initial burst. Since the absence of hepatic first pass metabolism, only a single active compound-tolterodine was detected in the plasma. This avoided the coexistence of two active compounds in plasma in the case of oral administration of tolterodine, which may lead to a difficulty in dose control due to the different metabolic capacity of patients. In the pharmacodynamic study, the influence of tolterodine PLGA microspheres on the inhibition of carbachol-induced rat urinary bladder contraction was more significant than that of tolterodine l-tartrate tablets. There were invisible changes in rat bladder slices between tolterodine-loaded PLGA microspheres group and tolterodine l-tartrate tablets group. These results indicate that the continuous inhibition of muscarinic receptor may offer an alternative therapy of urge incontinence.

Effect of the CYP2D6*10 genotype on tolterodine pharmacokinetics.

This study was conducted to investigate the effect of the reduced function allele CYP2D6*10, which can be the cause of an intermediate metabolizer (IM), on tolterodine pharmacokinetics. Tolterodine is mainly metabolized to an active 5-hydroxymethyl metabolite (5-HM) by CYP2D6, and 5-HM is also metabolized by CYP2D6. Asian and white healthy volunteers (n = 108) received once daily multiple doses of tolterodine, and the serum concentrations of tolterodine and 5-HM were measured. All subjects were genotyped for CYP2D6. Tolterodine exposures [area under the curve (AUC)] increased in order of CYP2D6*1/*1 [extensive metabolizer (EM)] < CYP2D6*1/*10 < CYP2D6*10/*10 < CYP2D6*5/*10. It was expected that the order of 5-HM exposure would be reversed. However, the 5-HM AUC increased in the same order as that of tolterodine. This phenomenon was explained by considering CYP2D6 mediation of both production and elimination of 5-HM. The tolterodine and 5-HM exposures in CYP2D6*10/*10 were statistically higher than those for CYP2D6*1/*1 (3- and 1.5-fold, respectively). In CYP2D6*4/*4 [poor metabolizer (PM)], 5-HM was not produced and tolterodine exposure was 20-fold higher than that in CYP2D6*1/*1. With consideration for higher protein binding of tolterodine than 5-HM, the exposure as a sum of the unbound fraction of tolterodine and 5-HM (active moiety) in CYP2D6*10/*10 was 1.8-fold higher than that in CYP2D6*1/*1 and was also higher than that in CYP2D6*4/*4. Simulation using the values of EM and PM demonstrated that the maximum possible active moiety exposure was around the observed values of CYP2D6*5/*10, which were 1.9-fold higher than those for CYP2D6*1/*1. This is the first report to provide an example in which the IM shows higher exposure to pharmacological active moiety than the EM and PM.