Donepezil

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.

Description

Donepezil is another “nonclassic,” centrally acting, reversible, noncompetitive AChEI that was approved in 1997 for treatment of mild-to-moderate AD and dementia. Its selectivity for AChE is 570- to 1,250-fold that for butyrylcholinesterase, and it also exhibits greater affinity for brain AChE than for AChE in the periphery.

The Uses of Donepezil

Acetylcholine is a neurotransmitter involved in neural signaling throughout the body. Donepezil is a reversible acetylcholinesterase inhibitor that readily crosses the blood-brain barrier to reduce the breakdown of acetylcholine. It has a half-life in circulation of about 70 hours. As acetylcholine modulates plasticity, excitability, and arousal in the central nervous system, donepezil is commonly used in the treatment of Alzheimer’s disease to improve cognition, memory, and behavior. In this way, it is intended to prevent or reverse dementia. Studies on these effects have been equivocal, indicating that more research into the therapeutic potential of donepezil is warranted.[Cayman Chemical]

Indications

Donepezil, administered orally or via transdermal delivery system, is indicated for the treatment of dementia of the Alzheimer's type. It is also available as an extended-release capsule in combination with memantine for the treatment of moderate-to-severe dementia of the Alzheimer's type in patients previously stabilized on 10mg of donepezil hydrochloride once daily.
Off-label uses include the management of vascular dementia, Parkinson's Disease-associated dementia, and Lewy body dementia, amongst others.

Background

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. A donepezil transdermal delivery system, Adlarity, was approved by the FDA in March 2022 for the treatment 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.

What are the applications of Application

Donepezil is shown to increase levels of cortical acetylcholine

Pharmacokinetics

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.