17th May 2025

Delirium

Delirium is an acute global disorder of the central nervous system function characterised by altered cognition, awareness, and attention.

As elderly patients’ central nervous system become more sensitive to neurochemical imbalances, all sedative medications can easily cause decompensation and delirium:

• Opioids
• Benzodiazepines
• Z-drugs for insomnia
• First generation antihistamines
• Antidepressants
• Antipsychotics
• Anticholinergics
• Antiemetics
• General anaesthesia

Steroids are well known to cause confusion and cognitive impairment, and in severe cases, hallucinations and delusions.

Medications that cause arrhythmias also have the potential to cause delirium. For instance, beta blockers and Digoxin cause bradycardia and may disrupt blood flow to the brain.

Anticholinergic burden

Anticholinergic medications are associated with many side effects to which the elderly are more susceptible:

• Cognitive impairment
• Confusion
• Drowsiness
• Ataxia
• Headache
• Hallucination
• Blurred vision (due to dry eyes)
• Dry mouth
• Nausea and vomiting
• Tachycardia and palpitations
• Urinary retention
• Constipation
• Reduced sweating

Anticholinergics not only can precipitate acute conditions such as acute closed angle glaucoma, but they are also associated with higher chance of hospital admission, longer length of stay and greater incidence of falls. Therefore, they should be avoided in elderly patients if possible.

Anticholinergic burden (ACB) is the cumulative measure of anticholinergic effect on an individual taking one or more drugs with anticholinergic activity. The ACB score for each patient can be calculated by adding up the score of each medication they are taking. A higher score represents a higher likelihood of adverse effects. Each 1-point increase in ACB total score is suggested to result in decline of MMSE score of 0.33 points and around 80% increase in mortality risk over 2 years.

Table 2. ACB score for different drugs

Levodopa is often combined with a peripheral blocker of dopamine metabolism for managing Parkinson’s disease, such as dopa decarboxylase inhibitor (e.g., Carbidopa, Benserazine), monoamine oxidase B (MAO-B; e.g., Selegiline, Rasagiline), and catechol‑O‑methyl transferase (COMT) inhibitor (e.g., Tolcapone, Entacapone). Topical dopamine agonist in the form of a patch, usually containing Rotigotine, can be given to patients who cannot comply with oral medications. First generation antipsychotics should be avoided in Parkinson’s patients as they can exacerbate extrapyramidal symptoms (EPS). Management of drug-induced EPS is Procyclidine.

In patients with dementia, antimuscarinics can more easily cause decompensation of cerebral function and delirium. When prescribing and reviewing an elderly patient’s drug chart, we should be aware of the high ACB medications and try to switch them to drugs with lower ACB scores.