Donepezil Stats & Data
COc1cc2CC(CC3CCN(CC3)Cc3ccccc3)C(=O)c2cc1OCADEBPBSSDYVVLD-UHFFFAOYSA-NPharmacology
DrugBankDescription
In 2016, the global burden of dementia was estimated to be 43.8 million, demonstrating a significant increase from a global prevalence of 20.2 million in 1990. Donepezil, also known as Aricept, is a piperidine derivative acetylcholinesterase inhibitor used in the management of the dementia of Alzheimer's Disease, and in some cases, is used to manage other types of dementia. Donepezil was first approved by the FDA in 1996, and its extended-release form was approved in combination with Memantine in 2014 to manage moderate and severe forms of Alzheimer's dementia. Though it does not alter the progression of Alzheimer's disease, donepezil is effective in managing the symptoms of its associated dementia.
Mechanism of Action
The commonly accepted cholinergic hypothesis proposes that a portion of the cognitive and behavioral decline associated with Alzheimer's are the result of decreased cholinergic transmission in the central nervous system. Donepezil selectively and reversibly inhibits the acetylcholinesterase enzyme, which normally breaks down acetylcholine. The main pharmacological actions of this drug are believed to occur as the result of this enzyme inhibition, enhancing cholinergic transmission, which relieves the symptoms of Alzheimer's dementia. In addition to the above, other mechanisms of action of donepezil are possible, including the opposition of glutamate-induced excitatory transmission via downregulation of NMDA receptors and the regulation of amyloid proteins, which have demonstrated significant effects on the disease process of Alzheimer's. Other possible targets for donepezil may also include the inhibition various inflammatory signaling pathways, exerting neuroprotective effects.
Pharmacodynamics
By inhibiting the acetylcholinesterase enzyme, donepezil improves the cognitive and behavioral signs and symptoms of Alzheimer's Disease, which may include apathy, aggression, confusion, and psychosis.
Metabolism
Donepezil is metabolized by first pass metabolism in the liver, primarily by CYP3A4, in addition to CYP2D6. After this, O-dealkylation, hydroxylation, N-oxidation, hydrolysis, and O-glucuronidation occur, producing various metabolites with similar half-lives to the unchanged parent drug. A study of the pharmacokinetics of radiolabeled donepezil demonstrated that about 53% of plasma radioactivity appeared as donepezil in the unchanged form, and 11% was identified as the metabolite 6-O-desmethyl donepezil, which exerts similar potency inhibition of the acetylcholinesterase enzyme. This drug is heavily metabolized to four primary metabolites, two of which are considered pharmacologically active, as well as to multiple inactive and unidentified metabolites.
Absorption
Donepezil is slowly absorbed via the gastrointestinal tract after oral administration. Tmax is 3 to 4 hours with a bioavailability of 100% and steady-state concentrations are attained within 15 to 21 days of administration. The Tmax in one pharmacokinetic study determined a Tmax of 4.1 ± 1.5 hours. The Cmax of 5 mg donepezil tablets is estimated to be 8.34 ng/mL, according to the Canadian monograph. The AUC of 5 mg donepezil tablets has been determined to be 221.90-225.36 ng.hr/mL.
Toxicity
LD50 The rat oral LD50 of donepezil is 32.6 mg/kg. Overdose information Signs and symptoms of overdose with cholinesterase inhibitors such as donepezil can include severe nausea and vomiting, bradycardia, hypotension, perspiration, seizures, muscle weakness respiratory depression, and collapse. Significant muscle weakness may result in death if the respiratory muscles are affected by donepezil overdose. To manage an overdose, anticholinergics can be employed as antidotes. Atropine at intravenous doses of 1.0 - 2.0 mg can be administered and titrated according to the clinical response. Consult the local poison control center for the most updated guidelines on the management of a donepezil overdose. Whether donepezil can be removed from the body with dialysis is unknown at this time.
Indication
Donepezil is indicated for the management of mild to moderate Alzheimer’s Disease at doses of 5 mg or 10 mg. It is also indicated for the management of moderate to severe Alzheimer’s Disease in a higher dose of 10 mg or 23 mg administered once daily. Off-label uses include the management of vascular dementia, Parkinson's Disease-associated dementia, and Lewy body dementia, among others. When combined with memantine, the extended-release form of donepezil is indicated to treat the symptoms of moderate to severe dementia.
Half-life
The average elimination half-life of donepezil is about 70 hours according to the results of various studies and the FDA label for donepezil.. One pharmacokinetic study determined the average terminal half-life to be 81.5±22.0 h
Protein Binding
Donepezil is 96% protein-bound, with approximately 75% binding to albumin and approximately 21% binding to alpha-1-glycoprotein.
Elimination
In a study of radiolabeled administration donepezil in healthy adults, 57% of measured radioactivity was identified in the urine, and 5% was identified in the feces.
Volume of Distribution
The volume of distribution of donepezil is 11.8 ± 1.7 L/kg for a 5-mg dose and 11.6 ± 1.91 L/kg for a 10-mg dose. It is largely distributed in the extravascular compartments. Donepezil crosses the blood-brain barrier and cerebrospinal fluid concentrations at the above doses have been measured at 15.7%. The volume of distribution at steady-state according to the FDA label for donepezil ranges from 12 - 16 L/kg.
Clearance
According to the FDA label, the average apparent plasma clearance of this drug is 0.13 – 0.19 L/hr/kg. A 5 mg dose of donepezil in healthy patients was shown to have a plasma clearance of 0.110±0.02 L/h/kg. In 10 patients diagnosed with alcoholic cirrhosis, showed a mean decrease in clearance by 20% when compared to the clearance in 10 healthy subjects. In 4 patients with severe renal impairment compared to 4 healthy subjects, no significant change in clearance was noted.