Plasma Donepezil Concentrations Research Articles

Preparation of Novel Donepezil Long‐Acting Injectable, IVL3003, and its Pharmacokinetic Study via Subcutaneous Injection in Dogs and Monkeys

AbstractBackgroundDonepezil is a selective oral acetylcholinesterase inhibitor to treat Alzheimer’s disease (AD). Most patients with AD need help with taking oral donepezil for forgetfulness etc. Therefore, long acting injectables (LAIs) can improve patient’s compliance and quality of life. Because of narrow therapeutic window of donepezil, precisely size controlled microsphere technology is needed for drug release control. We have developed IVL3003 as a novel sustained release monodisperse subcutaneous (SC) LAI of donepezil for one month using IVL‐DrugFluidics® technology. The purpose of this study is to evaluate the physicochemical characteristics of IVL3003 and investigate the inter‐species pharmacokinetic profile differences in beagle and monkey models.MethodVarious one month formulations of donepezil microspheres were prepared by IVL‐DrugFluidics®. Characterization of IVL3003 was performed by scanning electron microscopy (SEM), and the size distribution was measured by laser particle size analyzer (PSA). The amount of donepezil and encapsulation efficiency (EE, %) was determined by HPLC. Size distributions were expressed as span value and CV(%). Non‐clinical models were used to optimize formulations and to evaluate their pharmacokinetic properties. IVL3003 was administered to male beagle dogs (n = 3/group, 11 months old, body weight 9∼11 kg) and male cynomolgus monkeys (n = 3/group, 30∼50 months old, body weight 2.6∼3.3 kg). Plasma concentrations were monitored for one month.ResultsThe SEM images of the microspheres appeared spherical and smooth. Donepezil was well encapsulated and homogeneously. The EE(%) of microspheres was 97.5% and the residual solvent was 232.2 ppm. The span value was 0.25 and CV(%) was 10.01%. The plasma concentrations of donepezil were maintained for 28 days without any initial burst and had small individual variation. There was no big difference between species in plasma concentration and showed a similar PK profile in both.ConclusionsAs we postulated, narrow distribution of the particles was led to improvement of controlled‐release characteristics. These results proved the excellence of IVL‐DrugFluidics® as an ideal microsphere fabrication method in manufacturing uniform and monodispersed microspheres. Long‐acting injectable, IVL3003 is expected to increase the compliance and the safety in the treatment of Alzheimer’s patients. We have filed Ph I for IVL3003 recently as the 1st donepezil containing LAI.

Novel High‐Donepezil Loaded One‐Month Release Microspheres for Alzheimer’s Disease Treatment

AbstractBackgroundDonepezil is the most commonly prescribed medication for treating Alzheimer’s disease. However, the most commonly used once daily oral formulation or recently developed once or twice weekly patch formulations have side effects such as nausea, vomiting and weight loss or skin irritation, and the patient’s compliance with these medications is very low. One month release injectable of donepezil microspheres can be a good alternative to increase patient compliance and reduce these side effects. The biggest obstacle in the development of one month donepezil microspheres is that patients tend to feel pain at the injection site due to the large volume of dosage. We have developed novel donepezil microspheres with high drug contents which can improve patient compliance and medication convenience by lowering dosage volume at the injection site.MethodMono‐dispersed and spherical shaped donepezil microspheres with different drug contents were manufactured by membrane emulsification method. The morphology of the microspheres was observed by electron microscope, and the particle size distribution was measured by laser diffraction analysis. The donepezil contents in the microspheres were analyzed using HPLC. Pharmacokinetic studies were performed after a single injection in male SD rats. The concentration of donepezil in the plasma samples was determined by LC‐MS/MS.ResultDonepezil microspheres with three different drug contents (27%, 45% and 60%) were prepared successfully with high drug encapsulation efficiency. All the donepezil microspheres regardless of high drug content have a spherical shape and smooth surface with a narrow side distribution. Despite the high content of donepezil, the initial release was well controlled to less than 5% during the first 24 hours after injection. In rat PK studies of donepezil microspheres after a single injection, plasma donepezil concentration of all three formulations was kept within the therapeutic range for more than one month.ConclusionWe have developed novel donepezil microspheres with high drug contents and without initial burst release. These high donepezil‐loaded microspheres can improve patient compliance and medication convenience by lowering dosage volume at the injection site. Currently, this novel donepezil formulation is planned for commercialization after clinical trials.

Impact of Plasma Donepezil Concentration on Behavioral and Psychological Symptoms of Dementia in Patients with Alzheimer’s Disease

Background/Aims: The behavioral and psychological symptoms of dementia (BPSD) detract from the quality of life of not only dementia patients but also their family members and caregivers. Donepezil is used to treat Alzheimer’s disease and is metabolized via cytochrome P450 (CYP) 2D6 and CYP3A4/5. It is controversial whether donepezil improves or exacerbates BPSD. This study investigated the relationships among BPSD, the pharmacokinetics of donepezil including its metabolite, 6-O-desmethyl donepezil, genetic polymorphisms of CYPs and P-glycoprotein, and patient backgrounds in 52 patients with Alzheimer’s disease. Methods: BPSD were assessed using the Neuropsychiatric Inventory (NPI), with scores ≥20 points defined as severe BPSD. Plasma donepezil and 6-O-desmethyl donepezil concentrations were measured using liquid chromatography–tandem mass spectrometry. Results: Although significant relationships between NPI scores and plasma donepezil concentrations were not seen, none of the 15 patients (29%) with high plasma donepezil concentrations (≥60 ng/mL) developed severe BPSD. Polymorphisms of CYP2D6, CYP3A5, and ABCB1 did not influence NPI scores. There were no significant relationships between NPI and patient background factors such as dosing regimen, concomitant use of other drugs, or laboratory test results. Two patients who underwent multiple blood samplings over 2 years showed an inverse correlation between plasma donepezil concentrations and NPI scores. Discussion/Conclusions: These results indicate that higher plasma concentrations of donepezil contribute to preventing or alleviating rather than developing or deteriorating BPSD.

Impact of the CYP2D6 single nucleotide polymorphism on the concentration of and therapeutic response to donepezil in mild-to-moderate Alzheimer's disease

Donepezil was approved for the treatment of Alzheimer's disease (AD) but causes variable therapeutic responses. Thus, identifying specific genetic polymorphisms, which can predict a therapeutic response to donepezil, would enable a development of personalized strategy to treatment for patients with AD. The research aimed to exam the impact of the cytochrome P450 2D6 (CYP2D6) single nucleotide polymorphism (SNP) rs1080985 on the concentration of and therapeutic response to donepezil in AD. In total, 40 newly diagnosed AD patients who had a clinical dementia rating (CDR) of 0.5-2 and who were on donepezil were enrolled and followed up. Plasma concentrations of donepezil were determined after 6 months of donepezil treatment. Cognitive and functional statuses were evaluated annually during follow-up. The response to therapy was defined based on the change in CDR. At a mean of 21.8±5.7 months of follow-up, 10 of 40 patients (25.0%) were nonresponders to donepezil treatment. Patients who were homozygous for the G allele exhibited a higher concentration of donepezil and concentration-to-dose ratio than those with other genotypes. Furthermore, a significantly higher proportion of patients with the G/G genotype were responders than nonresponders (90.0% vs 50.0%, P=0.015, effect size of V: 0.457) to donepezil treatment. Conversely, patients carrying the C allele had a significantly high risk of poor responses to donepezil treatment (odds ratio: 9.00, 95% confidence interval: 1.611-50.275). The CYP2D6 SNP rs1080985 might be a useful pharmacogenetic marker of the long-term therapeutic response to donepezil in patients with AD.

The Impact of Dextran Sodium Sulfate-Induced Gastrointestinal Injury on the Pharmacokinetic Parameters of Donepezil and Its Active Metabolite 6-O-desmethyldonepezil, and Gastric Myoelectric Activity in Experimental Pigs.

Gastrointestinal side effects of donepezil, including dyspepsia, nausea, vomiting or diarrhea, occur in 20–30% of patients. The pathogenesis of these dysmotility associated disorders has not been fully clarified yet. Pharmacokinetic parameters of donepezil and its active metabolite 6-O-desmethyldonepezil were investigated in experimental pigs with and without small intestinal injury induced by dextran sodium sulfate (DSS). Morphological features of this injury were evaluated by a video capsule endoscopy. The effect of a single and repeated doses of donepezil on gastric myoelectric activity was assessed. Both DSS-induced small intestinal injury and prolonged small intestinal transit time caused higher plasma concentrations of donepezil in experimental pigs. This has an important implication for clinical practice in humans, with a need to reduce doses of the drug if an underlying gastrointestinal disease is present. Donepezil had an undesirable impact on porcine myoelectric activity. This effect was further aggravated by DSS-induced small intestinal injury. These findings can explain donepezil-associated dyspepsia in humans.

Pharmacological evaluation and safety of a donepezil patch.

Our aim was to assess the feasibility of transdermal delivery of donepezil and evaluate the pharmacokinetics (PK), pharmacodynamics (PD), and safety of donepezil patch in vitro and in vivo. Donepezil patches were applied to the skin of rabbits and humans for 7 days, then, the PK profiles were observed in a dose-dependent manner. Donepezil was continuously released from the patch for 7 days as compared to oral administration in hairless rats and rabbits. In hairless rats, peak acetylcholinesterase (AChE) inhibition of 34.7±2.0% was observed within 8 h after oral administration of 4 mg/head donepezil, and lasted for less than 24 h, consistent with changes in the plasma donepezil concentration. Peak AChE inhibition by the donepezil patch was equivalent to that in the orally administered group. Donepezil was released continuously from the patch for 7 days with a linear PK in both rats and rabbits. AChE activity inhibition was dependent on donepezil plasma concentration. The data exhibited excellent PK/PD correlation. There was no dermal irritation (erythema/edema) in placebo or donepezil patch group during the study period in minipigs. Thus, Dong-A's donepezil patch appeared to be generally safe and was well tolerated.

CYP2D6 Predicts Plasma Donepezil Concentrations in a Cohort of Thai Patients with Mild to Moderate Dementia.

PurposeDonepezil, a drug frequently used to treat dementia, is mainly metabolized by cytochrome P450 2D6 (CYP2D6). This study investigated the relationships between CYP2D6 genotype and activity scores as well as predicted phenotype of plasma donepezil concentrations in 86 Thai dementia participants.Materials and MethodsCYP2D6 was genotyped using bead-chip technology (Luminex xTAG® v.3). Steady-state trough plasma donepezil concentrations were measured using high-performance liquid chromatography.ResultsSixteen genotypes were found but the most frequent genotypes detected among our participants were CYP2D6*10/*10 (27.9%) and *1/*10 (26.7%). One-third of the participants had an activity score of 1.25 which predicted that they were normal metabolizers. The overall median (interquartile range) of plasma donepezil concentration was 51.20 (32.59–87.24) ng/mL. Normal metabolizers (NMs) had lower plasma donepezil concentrations compared to intermediate metabolizers (IMs) (41.15 (28.44–67.65) ng/mL vs 61.95 (35.25–97.00) ng/mL). Multivariate analysis showed that CYP2D6 activity score (r2 = 0.50) and the predicted phenotype (independent of dose) could predict the plasma donepezil concentration (r2 = 0.49).ConclusionPlasma donepezil concentration in NMs was lower compared to IMs. Additional studies with larger sample size and use of next-generation sequencing as well as its outcomes are warranted to confirm the benefit of using pharmacogenetic-guided treatment for donepezil.

Impact of CYP2D6, CYP3A5, and ABCB1 Polymorphisms on Plasma Concentrations of Donepezil and Its Metabolite in Patients With Alzheimer Disease.

Donepezil is one of the most commonly prescribed drugs for the treatment of Alzheimer disease. It is predominantly metabolized through CYP2D6 and to a lesser extent by CYP3A4/5. There are conflicting reports regarding the influence of CYP2D6, CYP3A5, and ABCB1 polymorphisms on the plasma concentration of donepezil. This study investigated the influence of these polymorphisms and sex on the plasma concentrations of donepezil and its active metabolite, 6-O-desmethyl donepezil (6ODD), in 47 patients with Alzheimer disease. Plasma donepezil and 6ODD concentrations were measured using liquid chromatography tandem mass spectrometry. Sex, the concomitant use of psychotropics, and CYP2D6, CYP3A5, and ABCB1 polymorphisms were analyzed as possible influencers. The mean plasma concentrations of donepezil and 6ODD were well correlated (R2 = 0.418). The mean plasma concentration ratio of donepezil to 6ODD (metabolic ratio) was significantly lower in intermediate metabolizers of CYP2D6 than in extensive metabolizers. The metabolic ratio in patients receiving psychotropics was significantly lower than in those not receiving psychotropics. Among intermediate metabolizers, patients positive for CYP3A5 *3/*3 showed a significant increase in plasma mean 6ODD concentrations when compared with those who did not express this gene (CYP3A5 *1/*1 or *1/*3). Results indicate that the mean plasma concentration ratio of donepezil to 6ODD is associated with CYP2D6 polymorphism and the concomitant use of psychotropics in patients with Alzheimer disease. In intermediate metabolizers, CYP3A5 may play a significant role in the metabolism of donepezil.

RAT AND DOG PHARMACOKINETIC STUDIES OF GB-5001, A ONCE MONTHLY DONEPEZIL INJECTABLE FOR ALZHEIMER’S DISEASE

Donepezil is an acetylcholinesterase inhibitor and is the most commonly prescribed medication for treating Alzheimer's disease. However, the currently marketed donepezil products are once daily oral formulations with side effects such as nausea, vomiting and weight loss, etc. and the patient's compliance is also very low. Recently, once or twice weekly donepezil patch formulations have been developed but these formulations still have disadvantages such as skin irritation, effect of sweating, shower, etc. on in vivo donepezil release rate. One month release injectable of donepezil using biodegradable polymers can be a good alternative to increase patient compliance and reduce these side effects or disadvantages. In this study, GB-5001, once monthly donepezil depot injectable was prepared using InnoLAMP technology, which enables easy mass production of uniform biodegradable microspheres. Pharmacokinetic studies were performed after a single intramuscular injection of GB-5001 in male SD rats and Beagle dogs. Dose dependency and PK parameters were evaluated by analyzing plasma donepezil concentration by LC/MS/MS after administering three different doses of GB-5001 in each species. GB-5001, one-month release donepezil microspheres with uniform size, was successfully prepared by InnoLAMP technology. In rat PK study of GB-5001 after a single intramuscular injection, plasma donepezil concentration was kept within the therapeutic range for more than one month. Three different doses of GB-5001 showed Tmax of 14 days and dose dependent Cmax values. Moreover, the area under the curve of GB-5001 was also observed to be increased with accordance with the dose. Dog PK study after a single intramuscular injection of GB-5001 at three different doses also showed similar in vivo donepezil release profiles and dose dependent Cmax and AUC values as in rat experiments. Using proprietary InnoLAMP platform technology, we successfully produced uniform sustained release donepezil microspheres for Alzheimer's disease. Dose dependent and longer than one month releasing PK Results in rats and dogs of this formulation, GB-5001, indicate that GB-5001 could be used as an excellent alternative delivery Methods of donepezil for Alzheimer's disease treatment. Currently, scale-up and GMP manufacturing processes are under development to initiate human clinical trial of GB-5001.

The Effects of Donepezil, an Acetylcholinesterase Inhibitor, on Impaired Learning and Memory in Rodents.

A previous study in humans demonstrated the sustained inhibitory effects of donepezil on acetylcholinesterase (AChE) activity; however, the effective concentration of donepezil in humans and animals is unclear. This study aimed to characterize the effective concentration of donepezil on AChE inhibition and impaired learning and memory in rodents. A pharmacokinetic study of donepezil showed a mean peak plasma concentration of donepezil after oral treatment (3 and 10 mg/kg) of approximately 1.2 ± 0.4 h and 1.4 ± 0.5 h, respectively; absolute bioavailability was calculated as 3.6%. Further, AChE activity was inhibited by increasing plasma concentrations of donepezil, and a maximum inhibition of 31.5 ± 5.7% was observed after donepezil treatment in hairless rats. Plasma AChE activity was negatively correlated with plasma donepezil concentration. The pharmacological effects of donepezil are dependent upon its concentration and AChE activity; therefore, we assessed the effects of donepezil on learning and memory using a Y-maze in mice. Donepezil treatment (3 mg/kg) significantly prevented the progression of scopolamine-induced memory impairment in mice. As the concentration of donepezil in the brain increased, the recovery of spontaneous alternations also improved; maximal improvement was observed at 46.5 ± 3.5 ng/g in the brain. In conclusion, our findings suggest that the AChE inhibitory activity and pharmacological effects of donepezil can be predicted by the concentration of donepezil. Further, 46.5 ± 3.5 ng/g donepezil is an efficacious target concentration in the brain for treating learning and memory impairment in rodents.

Pharmacokinetic and Pharmacodynamic Modeling and Simulation Analysis of Icure Donepezil Patch in Healthy Male Volunteers

Donepezil is a well-known reversible noncompetitive acetylcholinesterase inhibitor for the symptomatic treatment of Alzheimer’s disease. The purpose of this study was to characterize the pharmacokinetics of donepezil patch under development using mixed effect modeling analysis, and to expore optimal dosing regimens of the donepezil patch in comparison with donepezil oral formulation. PK data used in this analysis were from 60 Korean, healthy, male subjects in two Phase 1 studies, where all the subjects received single or multiple doses of donepezil patch of 43.75, 87.5, and 175 mg, and 12 of them received single oral dose of donepezil, 10 mg followed by single dose of donepezil patch. Concentrations of donepezil were measured using validated LC/MS-MS. Donepezil PK were analyzed by nonlinear mixed effect modeling implemented in NONMEM (version 7.3). The PK modeling analysis were conducted seqentially for oral formulation and patch, which describes the data of oral formulation compared to simultaneous analysis of both oral and patch formulations. The final model predicted the real, observed concentration data reasonably well. The Monte-Carlo simulation for plasma donepezil concentration predicted that overall, exposure to plasma donepezil is similar between donepezil 10 mg oral dosing every 24 hours and donepezil patch 175 mg every 72 hours, and between donepezil 5 mg oral dosing every 24 hours and donepezil patch 87.5 mg every 72 hours We developed a population PK model describing the plasma PK of donepezil patch formulation and compared it with that of donepzeil oral formulation in healthy Korean adult males. PK simulation based on the final PK model suggested that donepezil 175 mg patch every 72 hours shows similar concentration profile with oral dosing of donepezil 10 mg every 24 hours, and 87.5 mg patch every 72 hours with oral dosing of 5 mg every 24 hours.

Whole-Body Distribution of Donepezil as an Acetylcholinesterase Inhibitor after Oral Administration in Normal Human Subjects: A 11C-donepezil PET Study.

Objective(s):It is difficult to investigate the whole-body distribution of an orally administered drug by means of positron emission tomography (PET), owing to the short physical half-life of radionuclides, especially when 11C-labeled compounds are tested. Therefore, we aimed to examine the whole-body distribution of donepezil (DNP) as an acetylcholinesterase inhibitor by means of 11C-DNP PET imaging, combined with the oral administration of pharmacological doses of DNP.Methods:We studied 14 healthy volunteers, divided into group A (n=4) and group B (n=10). At first, we studied four females (mean age: 57.3±4.5 y), three of whom underwent 11C-DNP PET scan at 2.5 h after the oral administration of 1 mg and 30 µg of DNP, respectively, while one patient was scanned following the oral administration of 30 µg of DNP (group A). Then, we studied five females and five males (48.3±6.1 y), who underwent 11C-DNP PET scan, without the oral administration of DNP (group B). Plasma DNP concentration upon scanning was measured by tandem mass spectrometry. Arterialized venous blood samples were collected periodically to measure plasma radioactivity and metabolites. In group A, 11C-DNP PET scan of the brain and whole body continued for 60 and 20 min, respectively. Subjects in group B underwent sequential whole-body scan for 60 min. The regional uptake of 11C-DNP was analyzed by measuring the standard uptake value (SUV) through setting regions of interest on major organs with reference CT.Results:In group A, plasma DNP concentration was significantly correlated with the orally administered dose of DNP. The mean plasma concentration was 2.00 nM (n=3) after 1 mg oral administration and 0.06 nM (n=4) after 30 µg oral administration. No significant difference in plasma radioactivity or fraction of metabolites was found between groups A and B. High 11C-DNP accumulation was found in the liver, stomach, pancreas, brain, salivary glands, bone marrow, and myocardium in groups A and B, in this order. No significant difference in SUV value was found among 11C-DNP PET studies after the oral administration of 1 mg of DNP, 30 µg of DNP, or no DNP.Conclusion:The present study demonstrated that the whole-body distribution of DNP after the oral administration of pharmacological doses could be evaluated by 11C-DNP PET studies, combined with the oral administration of DNP.

Clinical Response to Donepezil in Mild and Moderate Dementia: Relationship to Drug Plasma Concentration and CYP2D6 and APOE Genetic Polymorphisms.

The clinical response to donepezil in patients with mild and moderate dementia was investigated in relation to the drug plasma concentration and APOE and CYP2D6 polymorphisms. In a prospective naturalistic observational study, 42 patients with Alzheimer's disease (AD) and AD with cerebrovascular disease who took donepezil (10 mg) for 12 months were evaluated. Their DNA was genotyped, and the donepezil plasma concentrations were measured after 3, 6, and 12 months. Good responders scored ≥-1 on the Mini-Mental State Examination at 12 months in comparison to the baseline score. The study results indicated the good response pattern was influenced by the concentration of donepezil, but not by APOE and CYP2D6 polymorphisms.

Increased plasma donepezil concentration improves cognitive function in patients with dementia with Lewy bodies: An exploratory pharmacokinetic/pharmacodynamic analysis in a phase 3 randomized controlled trial

ObjectiveTo investigate whether increasing plasma donepezil concentration further improves cognitive function and neuropsychiatric symptoms without compromising safety in patients with dementia with Lewy bodies (DLB). MethodsWe analyzed data from a 12-week phase 3 trial of donepezil (5 and 10mg/day) in patients with DLB. The contribution of factors affecting plasma donepezil concentration was evaluated using multivariate regression analysis. The relationships between plasma donepezil concentration and efficacy (cognitive function as measured by the Mini-Mental State Examination [MMSE], hallucinations and cognitive fluctuation), or safety (blood pressure, pulse rate, body weight, and parkinsonism as measured by the Unified Parkinson's Disease Rating Scale part III) were assessed by scatterplots and Pearson correlation. ResultsThe data of 87 patients were used in the analyses. Plasma donepezil concentration increased proportionally with increasing dose from 5 to 10mg/day. The dose (contribution rate: 0.39, p<0.0001) and age (contribution rate: 0.12, p=0.0003) were statistically significant contributing factors affecting plasma donepezil concentration. Plasma donepezil concentration correlated significantly with improvement of MMSE score (p=0.040), but no significant correlations were found with the change in other tested parameters. ConclusionsPlasma donepezil concentration correlated positively with change in cognitive function without affecting safety, and was affected mainly by dose and to a lesser extent by age. Therefore, for patients in whom safety concerns are not found at donepezil 5mg/day, increasing the dose to 10mg/day to increase plasma concentration is worthwhile to further improve cognitive function.

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

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

Single dose pharmacokinetics of the novel transdermal donepezil patch in healthy volunteers.

BackgroundDonepezil is an acetylcholinesterase inhibitor indicated for Alzheimer’s disease. The aim of this randomized, single-blind, placebo-controlled, single-dose, dose-escalation study was to investigate the safety, tolerability, and pharmacokinetics of the donepezil patch in healthy male subjects.MethodsEach healthy male subject received a single transdermal donepezil patch (72 hours patch-on periods) of 43.75 mg/12.5 cm2, 87.5 mg/25 cm2, or 175 mg/50 cm2. Serial blood samples were collected up to 312 hours after patch application. The plasma concentrations of donepezil were determined by using a validated liquid chromatography–tandem mass spectrometry method. Pharmacokinetic parameters were obtained by noncompartmental analysis. Tolerability of the patches and performance of the patches (adhesion, skin irritation, residual donepezil content in the patch) were assessed throughout the study.ResultsThe study was completed by 36 healthy subjects. After patch application, the maximal plasma donepezil concentration (Cmax) and the area under the curve (AUC) increased in a dose-proportional manner. Median time to Cmax was ~74–76 hours (~2–4 hours after patch removal), and mean t1/2β was ~63.77–93.07 hours. The average donepezil residue in the patch after 72 hours was ~73.9%–86.7% of the loading dose. There were neither serious adverse events nor adverse events that lead to discontinuation. Skin adhesion of the patch was good in 97.2% of the subjects. All skin irritations after patch removal were mild and were resolved during the study period.ConclusionThe donepezil patch appeared to be generally well tolerated and adhesive. Pharmacokinetic analysis of the donepezil patch demonstrated linear kinetics.

Dose-dependent sigma-1 receptor occupancy by donepezil in rat brain can be assessed with 11C-SA4503 and microPET

Sigma-1 receptor agonists are under investigation as potential disease-modifying agents for several CNS disorders. Donepezil, an acetylcholinesterase inhibitor used for the symptomatic treatment of Alzheimer's disease, is also a high-affinity sigma-1 agonist. The objectives of the present study were to investigate if the sigma-1 agonist tracer (11)C-SA4503 and microPET can be used to determine sigma-1 receptor occupancy (RO) of donepezil in the rat brain; to establish RO of donepezil at doses commonly used in rodent behavioural studies; and to determine the effective plasma concentration of donepezil required for 50% of max-min occupancy (EC50). Male Wistar rats were pre-treated with donepezil (0.1 to 10mg/kg) for about 1h before microPET scans using (11)C-SA4503. The total distribution volume (V T) of the tracer was determined by Logan graphical analysis using time activity curves from arterial plasma and regions of interest drawn around the entire brain and individual brain regions. RO by donepezil was calculated from a modified Lassen plot, and ED50 was estimated from the sigmoidal dose-response curves obtained when the RO was plotted against log donepezil dose. A dose-dependent reduction was observed for V T in the whole brain as well as individual brain regions. RO increased dose-dependently and was 93% at 10mg/kg. ED50 was 1.29mg/kg. Donepezil, in the common dose range, was found to dose-dependently occupy a significant fraction of the sigma-1 receptor population. The data indicate that it is possible to determine sigma-1 RO by an agonist drug in rat brain, using (11)C-SA4503 and microPET.

Concentration of Donepezil to the Cognitive Response in Alzheimer Disease

Donepezil has been approved, and higher dosages are recommended for the treatment of Alzheimer disease (AD). However, a few studies have reported different cognitive responses in patients with AD treated with donepezil without measuring the concentration. We evaluated the relationships between the therapeutic responses and plasma concentrations of donepezil in various cognitive domains using the Cognitive Ability Screening Instrument among 37 patients with newly diagnosed mild stage AD taking donepezil 5 mg/d. Among the 9 cognitive domains in the Cognitive Ability Screening Instrument, the long-term memory domain had the highest improvement ratio (81.1%) compared with the other domains. An increased donepezil plasma concentration [mean (SD), 75.14 (32.16) ng/mL] was significantly associated with the improvement of long-term memory (P = 0.045; odds ratio, 0.959; 95% confidence interval, 0.920-0.999) after adjusting for age, sex, education, and apolipoprotein E genotype. Although there are some limitations in our study, these findings indicate that a higher concentration of donepezil improves long-term memory in patients with mild stage AD and imply the possible benefits in the advanced stage of AD for relatively preserved long-term memory.

Bioequivalence Study of Donepezil Hydrochloride Tablets in Healthy Male Volunteers

The objective of this study was to investigate the bioequivalence of two formulations of 5 mg donepezil HCL tablets: Tonizep as the test and Aricept as the reference. The two products were administered as a single oral dose according to a randomized two-phase crossover with a 3-week washout period in 20 healthy Thai Male volunteers. After drug administration, serial blood samples were collected over a period of 216 hours. Plasma donepezil concentrations were measured by high performance liquid chromatography with UV detection. Pharmacokinetic parameters were analyzed based on noncompartmental analysis. The logarithmically transformed data of AUC0–∞ and Cmax were analyzed for 90% confidence intervals (CI) using ANOVA. The mean (90% CI) values for the ratio of AUC0–∞ and Cmax values of the test product over those of the reference product were 1.08 (1.02–1.14) and 1.08 (0.99–1.17), respectively (within the bioequivalence range of 0.8–1.25). The median Tmax for the test product was similar to that of the reference product (2.0 hr), and the 90% CI for the Tmax difference between the two preparations was –0.19 to 0.29 hr and within the bioequivalence range of ± 20% of the Tmax of the reference formulation. Our study demonstrated the bioequivalence of the two preparations.

Dried Blood Spot Analysis of Donepezil in Support of a GLP 3-month Dose-Range Finding Study in Rats

Donepezil hydrochloride is a reversible acetyl cholinesterase inhibitor approved for Alzheimer disease treatment. As an alternate therapy, a donepezil hydrochloride transdermal patch is in development. Recommended nonclinical safety studies include a 3-month Good Laboratory Practice (GLP) dose-range finding (DRF) study prior to conducting the 2-year dermal carcinogenicity study in rats. Demonstration of systemic exposure is necessary to interpret the in vivo data. Previous nonclinical reports supporting oral dosing have utilized liquid chromatography tandem mass spectrometry (LC/MS/MS) to quantify donepezil concentrations in plasma. Smaller species with limited blood volumes do not allow serial sampling to derive the full pharmacokinetic profile from a single animal. Therefore, the option of another analytical method requiring decreased sample volumes is desirable as it would decrease the required number of animals while obtaining the complete profile. The dried blood spot (DBS) technique allows drug level measurement from a few microliters; however, the method is still not widely utilized in GLP studies. Because donepezil plasma levels are known by the oral route, DBS was used to bridge the previous oral data and to support a 13-week GLP DRF study for repeated topical application in rats, comparing oral administration with 4 topical formulations. The DBS method was validated and demonstrated robustness and reproducibility for application to the DRF study. The assay results were comparable to a previously reported plasma LC/MS/MS assay-derived pharmacokinetic profile and provided justification for selection of the topical formulation and dose levels for the subsequent dermal carcinogenicity study.