A 24-week, double-blind, placebo-controlled trial of donepezil in patients with Alzheimer's disease. Donepezil Study Group

The efficacy and safety of donepezil as a treatment for patients with mild to moderate Alzheimer's disease (AD) was investigated in a multicenter, double-blind study. Patients were randomly assigned to treatment with placebo (n = 162), 5 mg/d donepezil (n = 154), or 10 mg/d donepezil (n = 157) for 24 weeks followed by a 6-week, single-blind placebo washout. The primary efficacy measures were the cognitive portion of the Alzheimer's Disease Assessment Scale (ADAS-cog) and the Clinician's Interview Based Assessment of Change-Plus (CIBIC plus), with the Mini-Mental State Examination (MMSE), Clinical Dementia Rating Scale-Sum of the Boxes (CDR-SB), and patient rated Quality of Life (QoL) used as secondary measures. Cognitive function, as measured by the ADAS-cog, was significantly improved in the 5- and 10-mg/d donepezil groups as compared with the placebo group at weeks 12, 18, and 24. Clinician's global ratings on the CIBIC plus also improved in both the 5- and 10-mg/d donepezil groups relative to placebo. At the end of the 6-week placebo washout phase, ADAS-cog scores and CIBIC plus ratings were not significantly different for the three groups. Significant treatment benefits were also observed consistently in both the 5- and 10-mg/d groups on the MMSE and the CDR-SB, but there was no consistent effect on the patient-rated QoL. Cholinergic side effects (primarily diarrhea, nausea, and vomiting) were reported more often in the 10-mg/d group than either the 5-mg/d or placebo groups. Side effects were transient and generally mild in severity. These data indicate that donepezil is a well-tolerated drug that improves cognition and global function in patients with mild to moderate AD.

The efficacy and safety of donepezil in patients with Alzheimer's disease: results of a US Multicentre, Randomized, Double-Blind, Placebo-Controlled Trial. The Donepezil Study Group

This study evaluated the efficacy and safety of donepezil in patients with mild to moderately severe Alzheimer's disease, and examined the relationships between plasma donepezil concentration, red blood cell acetylcholinesterase (AChE) activity and clinical response. The trial was of a multicenter, double-blind, parallel-group design and patients were randomised to once-daily treatment with either donepezil (1, 3 or 5 mg) or placebo. The 12-week double-blind phase was followed by a 2-week single-blind placebo washout. 161 patients (55-85 years of age) entered the study and 141 completed treatment. Patients treated with donepezil showed dose-related improvements in the Alzheimer's Disease Assessment Scale-cognitive subscale score (ADAS-cog) and in MMSF scores. The improvements in ADAS-cog were statistically significantly greater with donepezil 5 mg/day than with placebo. There was a 50% reduction in the percentage of patients showing clinical decline with donepezil at 5 mg/day (11%) relative to placebo (20%). In addition, a statistically significant correlation between plasma concentrations of donepezil and AChE inhibition was demonstrated. A plateau of inhibition (76-84%) was reached at plasma donepezil concentrations > 50 ng/ml. The correlation between plasma drug concentrations and ADAS-cog (p = 0.014), MMSE (p = 0.023) and patient quality of life scores, assessed by the patient (p = 0.037) were also statistically significant, as was the correlation between AChE inhibition and change in ADAS-cog (p = 0.008). The incidence of treatment-emergent adverse events with all three dosages of donepezil (64-68%) was comparable to that observed with placebo (65%). Donepezil had no clinically significant effect on vital signs, haematology or clinical biochemistry tests. Importantly, donepezil was not associated with any hepatotoxicity, as observed with acridine-based cholinesterase inhibitors.

Donepezil nanosuspension intended for nose to brain targeting: In vitro and in vivo safety evaluation

The present study was to develop donepezil loaded nanosuspension for direct olfactory administration which reaches the brain and determining safety profile in Sprague-Dawley rats. Nanosuspension was prepared by ionic-crosslinking method. The developed nanosuspension was intranasally instilled into the nostrils of rats with the help of cannula (size 18/20) so that drug reached into the brain directly via nose to brain pathway. The nanosuspension had an average size of 150-200nm with a polydispersity index of 0.341. The donepezil concentration was estimated in the brain homogenate using HPLC method. The Cmax showed concentration of donepezil in brain and plasma as 7.2±0.86 and 82.8±5.42ng/ml, respectively, for drug suspension and concentration of donepezil in brain and plasma as 147.54±25.08 and 183.451±13.45ng/ml, respectively, for nanosuspension at same dose of 0.5mg/ml when administered intranasally (p<0.05). The in vivo safety evaluation studies showed that no mortality, hematological changes, body weight variations and toxicity in animals was observed, when nanosuspension was administered in different doses as compared to control group (normal saline). Donepezil loaded chitosan nanosuspension is a potential new delivery system for treatment of Alzheimer's disease, when transported via olfactory nasal pathway to the brain.

Metabolism and elimination of 14C-donepezil in healthy volunteers: a single-dose study

AIM

The aim of this study was to investigate the metabolism and elimination of donepezil HCl in humans, following the administration of a single 5 mg (liquid) oral dose containing a mixture of unlabelled and 14C-labelled donepezil.

METHODS

This was an open-label, non-randomized study in healthy male volunteers (n = 8). Characterization of donepezil metabolism and elimination was performed by analysing blood, urine and faecal samples collected over a 10-day period following drug administration. Each collected sample was assayed for total radioactivity, and aliquots from specified time-points and/or pooled samples were assayed for the presence of donepezil metabolites by thin-layer chromatography (TLC). Donepezil concentrations in plasma were determined by HPLC.

RESULTS

Recovery of radioactivity in subject samples averaged 72% of the administered dose. Recovery of the administered dose in urine (57%) was significantly greater than that recovered in faeces (15%). Unchanged donepezil accounted for the largest component of the recovered dose in each matrix. Three metabolic pathways were identified: (i) O-dealkylation and hydroxylation to metabolites M1 and M2, with subsequent glucuronidation to metabolites M11 and M12; (ii) hydrolysis to metabolite M4; and (iii) N-oxidation to metabolite M6. In plasma, the parent compound accounted for about 25% of the dose recovered during each sampling period, as well as of the cumulative dose recovered. The recovered residue showed higher levels of the hydroxylated metabolites M1 and M2 than of their glucuronide conjugates M11 and M12, respectively. In urine, the parent compound accounted for 17%, on average, of the dose recovered from each pooled sample, as well as of the total recovered dose. The major metabolite was the hydrolysis product M4, followed by the glucuronidated conjugates M11 and M12. In faeces, the parent compound also predominated, although it accounted for only 1%, of the recovered dose. A large percentage of the radioactivity in faeces consisted of unidentified very polar metabolites, which were retained at the TLC origin. Of the extracted metabolites, the hydroxylation products M1 and M2 were the most abundant, followed by the hydrolysis product M4 and the N-oxidation product M6.

CONCLUSIONS

Donepezil is hepatically metabolized and the predominant route for the elimination of both parent drug and its metabolites is renal, as 79% of the recovered dose was found in the urine with the remaining 21% found in the faeces. Moreover, the parent compound, donepezil, is the predominant elimination product in urine. The major metabolites of donepezil include M1 and M2 (via O-dealkylation and hydroxylation), M11 and M12 (via glucuronidation of M1 and M2, respectively), M4 (via hydrolysis) and M6 (via N-oxidation).

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-β-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.

Impact of the CYP2D6 polymorphism on steady-state plasma concentrations and clinical outcome of donepezil in Alzheimer’s disease patients

OBJECTIVE

The aims of this study were to evaluate the impact of the CYP2D6 polymorphism on both the steady-state plasma concentrations (Cp) and the clinical outcome of donepezil, a selective acetylcholinesterase inhibitor used in the treatment of Alzheimer's disease (AD).

METHODS

Forty-two patients of Caucasian ethnicity affected by probable AD were included in the study. All had been receiving therapy with donepezil for at least 3 months: 31 patients with 5 mg/day and 11 patients with 10 mg/day. The CYP2D6 genotype was analysed, and donepezil Cp was measured by using high-performance liquid chromatography.

RESULTS

On the basis of their CYP2D6 genotype, 30 patients could be classified as homozygous extensive metabolizers (EM), 10 as heterozygous EM and 2 as ultrarapid metabolizers (UM). No poor metabolizer was found. The dose and body weight-corrected median donepezil Cp were slightly, though not significantly, lower in homozygous than in heterozygous EM (0.33 vs. 0.41 ng/ml/mg/kg, respectively). The latter group consistently showed a better clinical response to treatment, as measured by change in Mini-Mental State Examination score (median: 1.40 vs. -1.30, respectively). UM patients had lower Cp than EM patients and showed no clinical improvement.

CONCLUSIONS

Our preliminary data suggest that the CYP2D6 polymorphism influences both donepezil metabolism and therapeutic outcome and that a knowledge of a patient's CYP2D6 genotype together with donepezil concentration measurements might be useful in the context of improving the clinical efficacy of donepezil therapy.

Antinociceptive activity of the N-methyl-D-aspartate receptor antagonist N-(2-Indanyl)-glycinamide hydrochloride (CHF3381) in experimental models of inflammatory and neuropathic pain

N-(2-Indanyl)-glycinamide hydrochloride (CHF3381) is a novel low-affinity, noncompetitive N-methyl-d-aspartate receptor antagonist. The current study compared the antinociceptive effects of CHF3381 with those of gabapentin and memantine in in vitro and in vivo models of pain. In isolated rat spinal cord, CHF3381 and memantine, but not gabapentin, produced similar inhibition of the wind-up phenomenon. CHF3381 suppressed the maintenance of carrageenan-induced thermal and mechanical hyperalgesia in the rat with a minimum significantly effective dose (MED) of 30 mg/kg p.o. Memantine produced a partial reversal of both thermal and mechanical hyperalgesia (MED = 10 and 15 mg/kg i.p., respectively). Gabapentin reversed mechanical hyperalgesia (MED = 10 mg/kg s.c.), but did not affect thermal hyperalgesia. In the mouse formalin test, CHF3381 and memantine preferentially inhibited the late phase (MED = 30 and 20 mg/kg i.p., respectively); gabapentin inhibited only the late phase (MED = 30 mg/kg s.c.). Unlike morphine, CHF3381 chronic administration was not accompanied by the development of tolerance in the formalin test. Furthermore, morphine tolerance did not cross-generalize to CHF3381. In rats with a sciatic nerve injury, CHF3381 relieved both cold and mechanical allodynia (MED = 100 mg/kg p.o.). In contrast, memantine was inactive. Gabapentin blocked cold allodynia (MED = 30 mg/kg s.c.), but had marginal effects on mechanical allodynia. In diabetic neuropathy, CHF3381 reversed mechanical hyperalgesia (MED = 50 mg/kg p.o.). Memantine (15 mg/kg i.p.) produced an antinociceptive effect, whereas gabapentin (100 mg/kg p.o.) had no significant effect. Thus, CHF3381 may be useful for the therapy of peripheral painful neuropathies.

Comparison of the pharmacokinetics of E2020, a new compound for Alzheimer's disease, in healthy young and elderly subjects

E2020, a central-acting cholinesterase inhibitor, is now under clinical development as a potential therapeutic agent for senile dementia of Alzheimer type. In the current study, the authors compared the pharmacokinetics of this drug after single oral administration in 12 healthy young volunteers (20-27 years of age) and 6 elderly volunteers (65-82 years of age). The subjects received a single 2-mg oral dose of E2020 after a meal. Blood samples for determination of the drug level were collected over 168 hours after drug administration and were measured by specific high-pressure liquid chromatography methods with ultraviolet detection. E2020 was generally well tolerated by all subjects of both groups. The plasma elimination half-life of the beta-phase (t 1/2 beta) and time to maximum peak plasma concentration (tmax) were significantly longer in the elderly than in the young: t 1/2 beta, 103.8 +/- 40.6 versus 59.7 +/- 16.1 hours; and tmax, 5.2 +/- 2.8 versus 3.4 +/- 1.5 hours, respectively. There were no statistically significant differences in maximum peak plasma concentration and area under the curve between the two groups. The mean (+/- standard deviation) oral clearance (Cl/F) in the elderly (9.1 +/- 2.4 L/h) was similar to that in the young (10.6 +/- 2.7 L/h). The volume of distribution in the steady state (Vdss/F) was significantly larger in the elderly than that in the young: 1217.2 +/- 223.2 versus 852.5 +/- 147.7 L, respectively. These results suggested that the drug was absorbed more slowly and distributed more widely and thoroughly, but that its clearance from the body is essentially unaffected by age.(ABSTRACT TRUNCATED AT 250 WORDS)

Cyclooxygenase-2 inhibitors. Synthesis and pharmacological activities of 5-methanesulfonamido-1-indanone derivatives

The recent discovery of an alternative form cyclooxygenase (cyclooxygenase-2, COX-2), which has been proposed to play a significant role in inflammatory conditions, may provide an opportunity to develop anti-inflammatory drugs with fewer side effects than existing non-steroidal anti-inflammatory drugs (NSAIDs). We have now identified 6-[(2,4-difluorophenyl)-thio]-5-methanesulfonamido-1-indanone++ + (20) (L-745,337) as a potent, selective, and orally active COX-2 inhibitor. The structure-activity relationships in this series have been extensively studied. Ortho- and para-substituted 6-phenyl substitutents are optimal for in vitro potency. Replacement of this phenyl ring by a variety of heterocycles gave compounds that were less active. The methanesulfonamido group seems to be the optimal group at the 5-position of the indanone system. Compound 20 has an efficacy profile that is superior or comparable to that of the nonselective COX inhibitor indomethacin in animal models of inflammation, pain, and fever and appears to be nonulcerogenic within the dosage ranges required for functional efficacy. Although 20 and its oxygen linkage analog 2 (flosulide) are equipotent in the in vitro assays, compound 20 is more potent in the rat paw edema assay, has a longer t1/2 in squirrel monkeys, and seems less ulcergenic than 2 in rats.

Lack of pharmacokinetic or pharmacodynamic interaction between memantine and donepezil

BACKGROUND

Memantine, a low- to moderate-affinity, uncompetitive N-methyl-D-aspartate receptor antagonist, was approved in the US for treatment of moderate to severe Alzheimer's disease in October 2003.

OBJECTIVE

To determine whether an in vivo pharmacokinetic interaction exists between memantine and the acetylcholinesterase (AChE) inhibitor donepezil.

METHODS

In this open-label, multiple-dose study, 24 healthy subjects (aged 18-35 y) received oral administration of memantine 10 mg on day 1. Following a 14-day washout period, subjects were orally administered donepezil 5 mg once daily for 7 days on an outpatient basis. Beginning on day 22, the donepezil dosage was doubled for 22 days to the target dose of 10 mg once daily, with the last donepezil dose concomitantly administered with memantine 10 mg on day 43. Assessments included pharmacokinetic as well as safety parameters. In addition, AChE inhibition was measured in red blood cells by radiolabeled-enzyme assay following administration of donepezil alone and after a single memantine dose.

RESULTS

Data from 19 subjects who completed the study indicated no significant pharmacokinetic interactions between a single dose of memantine and multiple doses of donepezil. Percent maximum inhibition of AChE activity (mean +/- SD) by donepezil was 77.8 +/- 7.3% and not significantly different upon coadministration of a single dose of memantine (81.1 +/- 5.7%). Two subjects withdrew due to adverse events while taking donepezil alone. Single memantine doses administered with multiple donepezil doses were well tolerated.

CONCLUSIONS

The pharmacokinetic and pharmacodynamic data from this study indicated a lack of interaction between memantine and donepezil, suggesting that memantine and donepezil may be safely and effectively used in combination.

In vitro and in vivo evaluation of donepezil-sustained release microparticles for the treatment of Alzheimer's disease

The purpose of this work is to prepare donepezil microparticles (DM) and evaluate its advantage as a sustained release delivery system with subcutaneous injection once a month. DM was prepared using poly (d,l-lactide-co-glycolide) (PLGA) by an oil-water emulsion solvent evaporation technique. DM showed the loading ratio 13.2+/-2.1% (w/w) and yield 54.8+/-0.8% with mean particle size about 75mum. In vitro release of DM showed that donepezil completely released within 28 days in water, but the cumulative release percentages up to day 30 were 98.4% and 49.1% for phosphate buffer saline (PBS, pH 5.8) and PBS (pH 7.4), respectively. The in vivo experiment demonstrated that DM (90mg/kg) produced a sustained release process in rats, and reached steady-state concentration at day 8 and maintained until day 27 with steady-state levels of donepezil between 130.3+/-7.8 and 121+/-9.8ng/ml, which was accordance with that of free donepezil by oral application route (3mg/kgday). DM (90mg/kg) by subcutaneous infusion in rats produced the same pharmacological role as free donepezil (3mg/kgday) by oral application route. These results implicated that DM as a sustained release delivery strategy could substitute for its oral formulation for therapy of AD and come true its administration once a month.

A method for the simultaneous identification and quantitation of five superwarfarin rodenticides in human serum

A high-performance liquid chromatographic method with ultraviolet (UV) and fluorescence detection was developed for the analysis of one indandione and four hydroxycoumarin anticoagulant rodenticides in human serum. The superwarfarin rodenticides, chlorophacinone, bromadiolone, difenacoum, brodifacoum, and difethialone, can be identified and quantitated simultaneously with this method. After adding a buffer (pH 5.5), the anticoagulants were extracted from serum with chloroform-acetone. The organic phase was separated and evaporated to dryness, and the residue was subjected to chromatographic analysis. The anticoagulants were separated by reversed-phase chromatography and detected by UV absorption at 285 nm and by fluorescence at an excitation wavelength of 265 nm and an emission wavelength of 400 nm. Extraction efficiencies from 55 to 131% were obtained. The within-run precision ranged from 2.0 to 7.1% for UV detection and from 0.0 to 4.8% for fluorescence detection. Between-run precision ranged from 1.3 to 16.0% for UV detection and from 1.8 to 9.0% for fluorescence detection. The anticoagulants can be quantitated at serum concentrations down to 3-12 ng/mL for fluorescence detection and down to 20-75 ng/mL for UV detection. No interferences were observed with the related compounds warfarin and vitamin K1.

Simultaneous determination of donepezil (aricept) enantiomers in human plasma by liquid chromatography-electrospray tandem mass spectrometry

A rapid, sensitive and enantioselective LC-MS-MS method using deuterium-labeled internal standard was developed and evaluated for the simultaneous quantitative determination of donepezil enantiomers in human plasma without interconversion during clean-up process and measurement. The use of an avidin column allowed the separation of donepezil enantiomers, which were specifically detected by MS-MS without interference from its metabolites and plasma constituents. Evaluation of this assay method shows that samples can be assayed with acceptable accuracy and precision within the range from 0.0206 ng/ml to 51.6 ng/ml for both R-donepezil and S-donepezil. This analytical method was applied to the simultaneous quantitation of donepezil enantiomers in human plasma.

Characterization of cognitive deficits in a transgenic mouse model of Alzheimer's disease and effects of donepezil and memantine

Alzheimer's disease is characterized by a progressive decline in cognitive function and involves β-amyloid (Aβ) in its pathogenesis. To characterize cognitive deficits associated with Aβ accumulation, we analyzed PS1/APP mice overexpressing mutant presenilin-1 (PS1, M146L; line 6.2) and amyloid precursor protein (APP, K670N/M671L; line Tg2576), a mouse model of Alzheimer's disease with accelerated Aβ production. Age-dependent changes in working and spatial memory behaviors were investigated using Y-maze and Morris water maze tasks, respectively, in female PS1/APP mice at ages of 2, 4, 6, and 12 months. Significant deficits in working and spatial memory were observed from 4 and 6 months of age, respectively. Acute single-dose administrations of memantine, a low-to-moderate-affinity N-methyl-d-aspartate (NMDA) antagonist, showed improvements in working memory deficits at 4 months of age, whereas donepezil, an acetylcholinesterase (AChE) inhibitor, did not. However, both drugs improved spatial memory dysfunction at 6 months of age at therapeutically relevant doses. No age-related dramatic changes were observed in expression levels of several proteins relating to memory dysfunction and also the mechanisms of donepezil and memantine in the cerebral cortex of PS1/APP mice until 6 months of age. Taken together, these results suggest dysfunctions in cholinergic and/or glutamatergic transmissions may be involved in the cognitive deficits associated with Aβ toxicity. Since donepezil and memantine have been widely used for treating patients of Alzheimer's disease, these results also suggest that cognitive deficits in PS1/APP mice assessed in the Y-maze and Morris water maze tasks are a useful animal model for evaluating novel Alzheimer's disease therapeutics.

Developmental toxicity and toxicokinetics of two endothelin receptor antagonists in rats and rabbits

Embryo-fetal development studies with toxicokinetic evaluations were conducted in rats and rabbits after oral or intravenous administration of two endothelin receptor antagonists. In the rat studies, females were administered SB-217242 (0.01-300 mg/kg/day) orally or SB-209670 (0.01-50 mg/kg/day) intravenously from days 6-17 postcoitus (pc). External and visceral fetal examinations were performed at necropsy on day 21 pc. Maternal body weight and food consumption were decreased only at 300 mg/kg/day SB-217242. Embryolethality was seen at 300 mg/kg/day SB-217242. Decreased fetal body weight occurred at 300 mg/kg/day SB-217242 and 50 mg/kg/day SB-209670. Dose-dependent increases in the mean percentage of fetuses per litter with malformations were seen at > or = 50 mg/kg/day SB-217242 and > or = 10 mg/kg/day SB-209670. Craniofacial, great vessel, heart, and thyroid were the predominant malformations. In the rabbit studies, females were administered SB-217242 (0.01-50 mg/kg/day) orally or SB-209670 (0.01-25 mg/kg/day) intravenously from days 6-20 pc. There was no drug-related effect on maternal body weight or food consumption. Embryolethality was observed at 50 mg/kg/day of SB-217242. Dose-related increases in the mean percentage of fetuses per litter with malformations were seen at > or = 10 mg/kg/day SB-217242 and > or = 10 mg/kg/day SB-209670. The malformations were similar to those observed in the rat studies, except that craniofacial development was not altered by SB-209670. The malformations observed are consistent with the pattern of endothelin-1 gene expression described in mouse embryonic pharyngeal arches and heart, and with the craniofacial and cardiovascular malformations observed in endothelin-1-deficient mice. Given the known role for endothelins in development, and concordant malformations in rats and rabbits observed in this study, teratogenicity is likely to be a class effect of endothelin receptor antagonists.

An evaluation of the pharmacokinetics of donepezil HCl in patients with moderately to severely impaired renal function

AIM

The aim of this study was to evaluate the pharmacokinetics of donepezil HCl (5 mg) in patients with moderately to severely impaired renal function (creatinine clearance: <30 ml min(-1) 1.73 m(-2)), following the administration of single oral doses.

METHODS

This was an open-label, non-randomized study in patients with compromised renal function (n=11), and in age- and gender-matched healthy controls (n =11). Each subject received a single oral dose of 5 mg donepezil. Blood samples for pharmacokinetic measurements were taken at specified intervals for 17 days post-dose. Concentrations of donepezil in plasma were measured by HPLC with UV detection.

RESULTS

There were no statistical differences between the two groups for any of the pharmacokinetic parameters evaluated (ANOVA). Cmax (mean +/- SD) was 7.7+/-1.2 ng ml(-1) in healthy subjects and 8.3+/-3.2 ng ml(-1) in renally impaired patients. AUC(0-infinity) in healthy subjects and in renally impaired patients was 539+/-115 ng h ml(-1) and 640+/-150 ng h ml(-1), respectively. The mean half-life of donepezil was 86.7+/-23.3 h in healthy subjects and 91.3+/-40.9 h in the renally impaired patients. The drug was well tolerated by all study participants. There were no clinically significant changes in vital signs, clinical chemistry or ECG parameters.

CONCLUSIONS

These findings suggest that the pharmacokinetics of donepezil do not change in patients with moderately to severely impaired renal function.

Direct determination of E2020 enantiomers in plasma by liquid chromatography-mass spectrometry and column-switching techniques

High-performance liquid chromatography with column switching and mass spectrometry (MS) was applied to the on-line determination and resolution of the enantiomers of E2020 (acetylcholinesterase inhibitor) in plasma. This system employs two avidin columns and fast atom bombardment (FAB)-MS. A plasma sample was injected directly into an avidin trapping column (10 mm x 4.0 mm I.D.). The plasma protein was washed out from the trapping column immediately while E2020 was retained. After the column-switching procedure, E2020 was separated enantioselectivity in an avidin analytical column. The separated E2020 enantiomers were specifically detected by FAB-MS without interference from metabolites of E2020 and plasma constituents. The limit of quantification for each enantiomer of E2020 in plasma was 1.0 ng/ml and the intra- and inter-assay relative standard deviations for the method were less than 5.2%. The assay was validated for enantioselective pharmacokinetic studies in the dog.

Determination of donepezil, an acetylcholinesterase inhibitor, in human plasma by high-performance liquid chromatography with ultraviolet absorbance detection

A simple and sensitive high-performance liquid chromatographic (HPLC) method with UV absorbance detection is described for the quantification of donepezil, a centrally and selectively acting acetyleholinesterase inhibitor, in human plasma. After sample alkalinization with 0.5 ml of NaOH (0.1 M), the test compound was extracted from I ml of plasma using isopropanol-hexane (3:97, v/v). The organic phase was back-extracted with 75 microl of HCl (0.1 M) and 50 microl of the acid solution was injected into a C18 STR ODS-II analytical column (5 microm, 150x4.6 mm I.D.). The mobile phase consisted of phosphate buffer (0.02 M, pH 4.6), perchloric acid (6 M) and acetonitrile (59.5:0.5:40, v/v) and was delivered at a flow-rate of 1.0 ml/min at 40 degrees C. The peak was detected using a UV detector set at 315 nm, and the total time for a chromatographic separation was approximately 8 min. The method was validated for the concentration range 3-90 ng/ml. Mean recoveries were 89-98%. Intra- and inter-day relative standard deviations were less than 7.3 and 7.6%, respectively, at the concentrations ranging from 3 to 90 ng/ml. The method shows good specificity with respect to commonly prescribed psychotropic drugs, and it could be successfully applied for pharmacokinetic studies and therapeutic drug monitoring.

Safety and tolerability of the free-radical scavenger OPC-14117 in Huntington's disease. The Huntington Study Group

Oxidative damage due to free-radical generation in the setting of underlying defects of neuronal energy metabolism has been implicated as a pathogenetic mechanism for Huntington's disease (HD). The authors conducted a randomized, double-blind, placebo-controlled, multicenter trial of the tolerability of OPC-14117, a lipophilic free-radical scavenger that concentrates in the brain. Ambulatory patients with HD received OPC-14117 60 mg/d, 120 mg/d, 240 mg/d, or placebo and were assessed by the Unified Huntington's Disease Rating Scale (UHDRS) for 20 weeks, including 12 or 16 weeks of assigned treatment and 8 or 4 weeks of blinded withdrawal of the study drug. Tolerability was measured by the proportion of patients completing the initial 12-week course of treatment on their originally assigned regimen. Sixty-four patients were enrolled in the study, 56 of whom completed the 12 weeks of treatment. Treatment was discontinued in four patients (1 placebo, 1 60 mg/d, 2 240 mg/d) due to asymptomatic but persistent serum elevations of liver transaminase. Two patients (1 60 mg/d and 1 120 mg/d) withdrew because of increased involuntary movements, one patient (60 mg/d) withdrew due to persistent dry eyes, and one patient (120 mg/d) withdrew because of persistent vomiting. There were no significant differences between treatment arms in the primary measures of tolerability, the frequency and types of clinical adverse events, or the clinical/functional features of HD. OPC-14117 was safe and generally well tolerated; however, elevations of liver transaminase suggested that continued surveillance monitoring is warranted in conducting more long-term studies of this antioxidant therapy.

Rasagiline and its (S) enantiomer increase survival and prevent stroke in salt-loaded stroke-prone spontaneously hypertensive rats

The aim of this study was to determine whether chronic treatment with the selective MAO-B inhibitor rasagiline, N-propargyl-1-(R)-aminoindan (R-PAI), can prevent or delay stroke or improve its outcome in salt-loaded stroke-prone spontaneously hypertensive rats (SHRSP). The S-enantiomer of rasagiline, S-PAI a much weaker MAO inhibitor was included in the study in order to expose a possible contribution from MAO inhibition to any beneficial effect by R-PAI. SHRSP were isolated, fed rat stroke prone diet and given 1% NaCl instead of water. Drugs were administered in the drinking fluid for 84 days. Rats were grouped as follows: (1) Untreated control; (2) R-PAI 1 mg/kg/day; (3) R-PAI 3 mg/kg/day; (4) S-PAI 3 mg/kg/day; (5) S-PAI 6 mg/kg/day. Survival, stroke frequency and neurological severity score following stroke were determined. R-PAI at 3 mg/kg/day significantly increased cumulative survival from 56.09 +/- 1.77 days in the untreated to 73.6 +/- 2.22 days in the R-PAI treated; S-PAI at 6 mg/kg/day to 78.61 +/- 2.05 (censored at 84 days). In these groups stroke was delayed, its incidence was decreased and its outcome was less severe than in the control group. Proteinurea observed in the untreated rats and in both lower dose groups of R-PAI and S-PAI was absent in the higher dose groups of both drugs. Histological examination of the brains and kidneys showed that the effects on stroke and survival were associated with decreased infarcts and hemorrhages in the brains and decreased tubular nephropathy and glomerulopathy. The time-dependent rise in systolic blood pressure in the untreated rats was significantly attenuated only in the R-PAI group at 3 mg/kg/day but not in the S-PAI group. There were no significant effects on heart rate. MAO-B activity in the brain was 95% blocked by both doses of R-PAI but only 62% by S-PAI at 6 mg/kg/day. In salt-loaded SHRSP chronic therapy with either R-PAI or S-PAI prevented stroke and severe vascular lesions in the kidney. When stroke did occur its neurological outcome was less severe. The drugs were equipotent when they were given at a ratio of 1:2. The mechanism has yet to be elucidated. The differential effects of the drugs on blood pressure and MAO inhibition rule out either effect as the sole explanation.

CHF3381, a N-methyl-D-aspartate Receptor Antagonist and Monoamine Oxidase–A Inhibitor, Attenuates Secondary Hyperalgesia in a Human Pain Model

CHF3381 is a new low-affinity, noncompetitive N-methyl-D-aspartate (NMDA) receptor antagonist and reversible monoamine oxidase-A (MAO-A) inhibitor. The analgesic activity of CHF3381 was investigated in the heat-capsaicin human pain model and compared with those of gabapentin. Twenty-seven young, healthy male volunteers received a single oral dose of CHF3381 (500 mg), gabapentin (1,200 mg), or placebo in a randomized, double-blind, crossover study design. Measurements were done before and 135 to 145 minutes after treatment administration and included area of secondary hyperalgesia around the sensitized skin of the forearm (45 degrees C for 5 minutes followed by topical capsaicin for 30 minutes), area of secondary hyperalgesia after thermal sensitization of the thigh (45 degrees C for 3 minutes), heat pain detection thresholds (degrees C), and pain on a visual analogue scale after long thermal stimulation (45 degrees C for 1 minute). Compared with placebo, both gabapentin and CHF3381 significantly reduced the area of secondary hyperalgesia on the dominant forearm. Median (and interquartile range) percent values over baseline were 86% after placebo (69% to 100%), 56% (41% to 76%) after gabapentin (P < .001), and 67% (49% to 88%) after CHF3381 (P < .009). Both drugs also significantly decreased the area of secondary hyperalgesia on the dominant thigh. The other pain variables were not significantly affected. Adverse events, mainly fatigue and dizziness, were mild to moderate.

PERSPECTIVE

This article presents the antihyperalgesic effect of CHF3381, a new NMDA receptor antagonist and reversible MAO-A inhibitor, in a human pain model and might guide the proper selection of CHF3381 doses to be used in Phase 2 studies in patients with neuropathic pain.

Assessment of ruminal degradation, oral bioavailability, and toxic effects of anticoagulant rodenticides in sheep

OBJECTIVE

To assess the rate and extent of ruminal degradation of warfarin, chlorophacinone, and bromadiolone in vitro and determine the oral availability and clinical and hemostatic effects of each anticoagulant rodenticide in adult sheep.

ANIMALS

3 Texel sheep.

PROCEDURE

Samples of ruminal fluid were incubated with each of the anticoagulants to assess the kinetics of ruminal degradation over 24 hours. To determine the plasma kinetics of the anticoagulants, each sheep received each of the anticoagulants IV or via a rumenimplanted cannula at 2-month intervals (3 rodenticide exposures/sheep). At intervals during a 240- to 360- hour period after treatment, prothrombin time (PT) was measured, plasma anticoagulant concentration was assessed, and clinical signs of rodenticide poisoning were monitored. In plasma and rumen extracts, anticoagulant concentrations were determined via high-performance liquid chromatography.

RESULTS

In the rumen extracts, anticoagulants were slightly degraded (< 15%) over 24 hours. In vivo, oral availability of warfarin, chlorophacinone, and bromadiolone was estimated at 79%, 92%, and 88%, respectively. Although maximum PT was 80 seconds after chlorophacinone and bromadiolone treatments, no clinical signs of toxicosis were detected; PT returned to baseline values within 2 weeks.

CONCLUSIONS AND CLINICAL RELEVANCE

In sheep, warfarin, chlorophacinone, and bromadiolone were not degraded in the rumen but their bioavailabilities were high after oral administration; the kinetics of these compounds in sheep and other mammals are quite similar. These data suggest that the lack of susceptibility of ruminants to these anticoagulant rodenticides cannot be explained by either ruminal degradation or the specific toxicokinetics of these anticoagulants.

Quantitative determination of donepezil in human plasma by liquid chromatography/tandem mass spectrometry employing an automated liquid–liquid extraction based on 96-well format plates

An automated high-throughput liquid chromatography/tandem mass spectrometry (LC-MS/MS) method was developed for quantitative determination of donepezil in human plasma. 150 MicroL of plasma samples were placed in 2.2 mL 96-deepwell plates and both donepezil and loratadine (IS) were extracted from human plasma by liquid-liquid extraction (LLE), using hexane as the organic solvent. Robotic liquid handling workstations were employed for all liquid transfer and solution preparation steps and resulted in a short sample preparation time. After vortexing, centrifugation and freezing, the supernatant organic solvent was evaporated and reconstituted in a small volume of reconstitution solution. The method developed, includes a sample analysis performed by reversed phase LC-MS/MS, with positive ion electrospray ionization, using multiple reaction monitoring (MRM). The chromatographic run time was set for 2.0 min with a flow rate of 0.7 mL/min in a C18 analytical column. The method was significantly sensitive, specific, accurate and precise for the determination of donepezil in human plasma and had the shortest run time. The curve was proven to be linear for the concentration range of 0.1-100 ng/mL. After validation, the method was applied to the rapid and reliable quantitative determination of donepezil in a bioequivalence study after per os administration of a 5mg donepezil tablet.

Reduction of carry-over in column-switching HPLC/MS system with automated system washing procedure for highly sensitive direct analysis of donepezil in dog plasma

To solve the problem of carry-over--a persistent chromatographic challenge for bioanalytical assays with highly sensitive detector such as a mass spectrometry (MS)--a new on-line sample pretreatment HPLC/MS system using a column-switching technique was established. This system was designed to reduce carry-over based on a hydrophobic interaction mechanism using a washing function (multi-mobile phase flow system), as well as to remove impurities on-line in a mobile phase for the pretreatment. As a result, a washing function in this system was enabled to reduce carry-over and to remove impurities in a mobile phase by automatic operation. Therefore, concentration levels of donepezil (DH) in dog plasma as low as 10 pg/mL could be determined using this on-line sample pretreatment HPLC/MS system. In addition, method validation results of specificity, linearity, accuracy, precision, lower limit of quantitation (LLOQ), and carry-over demonstrated that this on-line sample pretreatment HPLC/MS system was robust and valid as a practical assay of drugs and metabolites in the biological samples.