Donepezil

Donepezil is an acetylcholinesterase inhibitor used in the treatment of mild to moderate Alzheimer's disease, and in some cases severe Alzheimer's disease under specialist supervision. It belongs to a class of medicines that work by reducing the breakdown of acetylcholine in the brain, a neurotransmitter that plays a critical role in memory, learning, and cognition. By inhibiting the enzyme acetylcholinesterase, donepezil increases the concentration of acetylcholine available for neurotransmission at synapses in the brain, thereby compensating partially for the cholinergic deficit that characterises Alzheimer's disease.

Understanding Alzheimer's Disease and Cholinergic Deficit

Alzheimer's disease is a progressive neurodegenerative condition in which specific populations of neurons, particularly those in regions important for memory formation, including the hippocampus and basal forebrain, are damaged and lost over time. Among the most consistently affected neuronal systems is the cholinergic system, which relies on acetylcholine as its signalling molecule. The resulting cholinergic deficit contributes significantly to the cognitive impairment seen in Alzheimer's, including difficulties with short-term memory, word-finding, planning, and orientation.

Donepezil does not halt or reverse the underlying disease process; it does not prevent neuronal loss or the deposition of amyloid plaques or tau tangles. Rather, it modestly but meaningfully improves cognitive function and day-to-day functioning in many patients by making better use of the diminishing cholinergic reserves in the brain.

Treatment Goals and Clinical Evidence

Clinical trials have demonstrated that donepezil significantly slows cognitive decline compared with placebo in patients with mild to moderate Alzheimer's disease. Patients and carers often report improvements in memory, attention, and the ability to carry out daily tasks. The medicine also appears to have modest beneficial effects on behavioural and psychological symptoms of dementia, such as agitation and apathy. Donepezil is typically initiated by a specialist in memory disorders or old age psychiatry and continued under the supervision of a GP, with regular reviews to assess ongoing benefit and tolerability.

How to Take Donepezil

Donepezil tablets are taken once daily, in the evening just before bedtime. Taking it at night helps to minimise nausea and dizziness, which are most common during the initial treatment period. The tablet can be swallowed whole with water. Orodispersible tablets can be placed on the tongue and allowed to dissolve without water — useful for people who have difficulty swallowing.

Treatment is started at 5 mg once daily. After four to six weeks, if this is well tolerated, the dose is usually increased to 10 mg once daily, which is the recommended maintenance dose for moderate to severe Alzheimer's disease.

Long-term Use

Donepezil does not cure Alzheimer's disease or halt progression, but it can improve cognitive function and help maintain daily functioning for a period of time. Regular review by the prescribing doctor or memory clinic is important to assess ongoing benefit and tolerability.

The initial dose of donepezil is 5mg once daily taken at bedtime. After a minimum of four weeks, the dose may be increased to 10mg once daily, which is the standard maintenance dose for most patients. In some patients with severe Alzheimer's disease, doses up to 10mg are used under specialist guidance; 10mg is the maximum recommended daily dose.

Donepezil is predominantly metabolised by the liver via CYP2D6 and CYP3A4 enzymes, and dose adjustment is not routinely required for patients with renal impairment. However, patients with significant hepatic impairment may require lower doses and close monitoring. Elderly patients do not require dose adjustment based on age alone. The orodispersible tablet formulation (which dissolves on the tongue) is available in both 5mg and 10mg strengths and provides a convenient alternative for patients who find swallowing difficult, a common issue in advanced dementia.

Common Side Effects

• Nausea (most common during the initial dose-increase period, usually settles after a few weeks)
• Diarrhoea
• Vomiting
• Muscle cramps
• Fatigue
• Insomnia or vivid dreams (due to increased cholinergic activity during sleep)
• Headache
• Dizziness
• Reduced appetite

Important Cardiac Warning

Donepezil can slow the heart rate (bradycardia) and, in rare cases, cause heart block. This is more significant in people with pre-existing heart conditions or those also taking other medicines that affect heart rate (such as beta-blockers or amiodarone). Tell your doctor if you experience fainting, dizziness, or a very slow heartbeat. Donepezil can also worsen peptic ulcers due to its effect on stomach acid production — tell your doctor if you have a history of stomach ulcers.

Cardiovascular Monitoring

Donepezil can cause bradycardia (a slowing of the heart rate) due to its cholinergic mechanism of action. This effect is generally mild and well tolerated but can be more significant in patients with pre-existing cardiac conduction abnormalities such as sick sinus syndrome or various degrees of heart block. A baseline ECG is often recommended before initiating treatment in patients with known cardiac disease. Patients taking other medicines that slow the heart rate, such as beta-blockers, digoxin, or certain antiarrhythmics, may be at increased risk of significant bradycardia.

Donepezil also increases gastric acid secretion via cholinergic stimulation, which raises the risk of peptic ulceration in susceptible patients, particularly those taking NSAIDs or aspirin concurrently. Patients at risk of gastrointestinal ulceration may require gastroprotective therapy alongside donepezil.

Use in Specific Populations

Donepezil should not be used during pregnancy or breastfeeding unless absolutely necessary, as its effects on the developing baby are not well established. Patients with severe hepatic impairment should use donepezil with caution. The medicine has the potential to exacerbate or unmask Parkinson's disease symptoms in susceptible individuals, due to increased cholinergic tone. Patients with asthma or chronic obstructive pulmonary disease should be monitored carefully, as cholinergic stimulation can cause bronchoconstriction. Anaesthetists should be informed that the patient is taking donepezil, as it can interact with suxamethonium and other neuromuscular blocking agents used during surgery.

• Hypersensitivity to donepezil hydrochloride, piperidine derivatives, or any excipient
• Known cardiac conduction abnormalities (sick sinus syndrome, uncontrolled heart block) without pacemaker
• Severe hepatic impairment (relative contraindication -- use only under specialist supervision)
• Pregnancy and breastfeeding (avoid unless strictly necessary)
• Active peptic ulcer disease (exercise caution -- consider gastroprotection)
• History of seizures not well controlled on antiepileptic therapy
• Co-administration with medicines that significantly slow heart rate without cardiac monitoring