Pharmacology Of Donepezil

Indication	For the palliative treatment of mild to moderate dementia of the Alzheimer's type.
Pharmacodynamics	Donepezil is a centrally acting reversible acetyl cholinesterase inhibitor. Its main therapeutic use is in the treatment of Alzheimer's disease where it is used to increase cortical acetylcholine. An early pathophysiological feature of Alzheimer's disease that is associated with memory loss and cognitive deficits is a deficiency of acetylcholine as a result of selective loss of cholinergic neurons in the cerebral cortex, nucleus basalis, and hippocampus. Donepezil is postulated to exert its therapeutic effect by enhancing cholinergic function. This is accomplished by increasing the concentration of acetylcholine through reversible inhibition of its hydrolysis by acetylcholinesterase. If this proposed mechanism of action is correct, donepezil's effect may lessen as the disease progresses and fewer cholinergic neurons remain functionally intact. There is no evidence that donepezil alters the course of the underlying dementing process.
Mechanism of action	Donepezil is a piperidine derivative that is a centerally active, reversible inhibitor of acetylcholinesterase. This drug is structurally unrelated to other anticholinesterase agents. Donepezil's proposed mechanism of action involves the reversible inhibition of cholinesterases (eg. acetylcholinesterase), which prevents the hydrolysis of acetycholine, and leads to an increased concentration of acetylcholine at cholinergic synapses. Evidence suggests that the anticholinesterase activity of donepezil is relatively specific for acetylcholinesterase in the brain.
Absorption	Donepezil is well absorbed with a relative oral bioavailability of 100% and reaches peak plasma concentrations in 3 to 4 hours.
Volume of distribution	12 L/kg
Protein binding	96%
Metabolism	Donepezil is metabolized by CYP 450 isoenzymes 2D6 and 3A4 in the liver and also undergoes glucuronidation. The main metabolite, 6-O-desmethyl donepezil, has been reported to inhibit AChE to the same extent as donepezil in vitro.
Route of elimination	Donepezil is both excreted in the urine intact and extensively metabolized to four major metabolites, two of which are known to be active, and a number of minor metabolites, not all of which have been identified.
Half life	70 hours
Clearance	apparent plasma cl=0.13 L/hr/kg
Toxicity	Symptoms of overdose include severe nausea, vomiting, salivation, sweating, bradycardia, hypotension, respiratory depression, collapse and convulsions. Increasing muscle weakness is a possibility and may result in death if respiratory muscles are involved.