15.8: Alzheimer’s Disease: Treatment

Alzheimer's Disease (AD), a neurodegenerative disorder, is pathologically identified by amyloid plaques and neurofibrillary tangles composed of tau protein. AD pharmacotherapy aims to manage cognitive symptoms, delay disease progression, and treat behavioral symptoms. The treatment is primarily symptomatic and palliative, with no definitive disease-modifying therapy available. Cholinesterase inhibitors, including donepezil (Aricept), rivastigmine (Exelon), and galantamine (Razadyne), are first-line treatments for the first two stages of AD. These drugs work by inhibiting acetylcholinesterase (AChE), thus enhancing cholinergic transmission in the brain. The loss of cholinergic neurons is a characteristic of AD. Common adverse effects of these inhibitors include nausea, diarrhea, vomiting, anorexia, tremors, bradycardia, and muscle cramps.

Memantine (Namenda), an NMDA antagonist, is used in moderate to severe stages of AD as an adjunct or alternative to cholinesterase inhibitors. It acts as an NMDA receptor antagonist, limiting calcium ion influx into neurons and preventing neuronal damage caused by excessive glutamate. Memantine is generally well-tolerated, with few dose-dependent adverse events reported. Often, it is given in combination with an AChE inhibitor due to its different mechanism of action and potential neuroprotective effects. For behavioral and psychiatric symptoms in dementia (BPSD), SSRIs or atypical antipsychotics can be used alongside cholinesterase inhibitors and memantine. Several other drugs, including cholinomimetic drugs, MAO type B inhibitors, and NMDA receptor inhibitors, have been explored to treat AD. Furthermore, antibodies targeting amyloid-beta (Aβ) have shown the potential to slow AD cognitive decline.

In summary, treating AD involves a multi-pronged approach focusing on symptom management, disease progression delay, and behavioral symptom treatment. However, these treatments do not alter the underlying neurodegenerative process of AD.

The goal of Alzheimer's disease or AD pharmacotherapy is to manage cognitive symptoms, delay disease progression, and treat behavioral symptoms, providing palliative and average short-term benefits.

Cholinesterase inhibitors like donepezil, rivastigmine, and galantamine are first-line treatments for mild or moderate AD. They work by inhibiting AChE in the CNS to enhance cholinergic transmission.

Side effects of cholinesterase inhibitors include nausea, vomiting, diarrhea, anorexia, tremors, bradycardia, and muscle cramps.

Memantine, an NMDA receptor antagonist, is used in later stages of AD as an adjunct to cholinesterase inhibitors.

It limits Ca²⁺ influx into neurons, preventing neuronal damage due to excessive glutamate.

Memantine is generally well-tolerated, with few dose-dependent adverse events reported.

For behavioral symptoms in AD, SSRIs or second-generation antipsychotics can be used alongside cholinesterase inhibitors and memantine.

Despite available treatments, AD remains incurable, with drugs only mitigating symptoms and improving quality of life.