11 Geriatrics
There has been a steady increase in the number of elderly people, defined as those over 65 years of age, since the beginning of the twentieth century. They formed only 4.8% of the population in 1901, increasing to 15.2% in 1981 and about 18% in 2001. In 2008, there were 4.8 million people over the age of 75 years in the UK. Their number is projected to increase to 5.8 million by 2018 and to 8.7 million by 2033 – a rise of 81% over 25 years. In addition, the number of people over 85 years of age is also projected to increase from 1.3 million in 2008 to 3.3 million in 2033. The number of centenarians is projected to increase from 11,000 in 2008 to 80,000 in 2033 (Office for National Statistics, 2010). The significant increase in the number of very elderly people will have important social, financial and health care planning implications.
Pharmacokinetics
Pharmacodynamics
Changes in pharmacodynamics in the elderly may be considered under two headings:
Reduced homeostatic reserve
Common clinical disorders
Dementia
Dementia is characterised by a gradual deterioration of intellectual capacity. Alzheimer’s disease (AD), vascular dementia (VaD), dementia with Lewy bodies and frontotemporal dementia are the most important diseases of cognitive dysfunction in the elderly. AD has a gradual onset, and it progresses slowly. Forgetfulness is the major initial symptom. The patient has difficulty in dressing and other activities of daily living. He or she tends to get lost in his or her own environment. Eventually, the social graces are lost. VaD is the second most important cause of dementia. It usually occurs in patients in their 60s and 70s, and is more common in those with a previous history of hypertension or stroke. It is commonly associated with mood changes and emotional lability. Physical examination may reveal focal neurological deficits. A number of drugs and other conditions cause confusion in the elderly, and their effects may be mistaken for dementia. These are listed in Box 11.1.
In patients with AD, damage to the cholinergic neurones connecting subcortical nuclei to the cerebral cortex has been consistently observed. Postsynaptic muscarinic cholinergic receptors are usually not affected, but ascending noradrenergic and serotonergic pathways are damaged, especially in younger patients. Based on those abnormalities, several drugs have been investigated for the treatment of AD. Lecithin, which increases acetylcholine concentrations in the brain, 4-aminopyridine, piracetam, oxitacetam and pramiracetam, all of which stimulate acetylcholine release, have been tried, but have produced no, or unimpressive, improvements in cognitive function. Anticholinesterases block the breakdown of acetylcholine and enhance cholinergic transmission. Donepezil, galantamine and rivastigmine are recommended for treatment of patients with AD of moderate severity only (those with a Mini Mental State Examination (MMSE) score of between 10 and 20 points; NICE, 2009). Donepezil is a piperidine-based acetylcholinesterase inhibitor. It has been shown to improve cognitive function in patients with mild to moderately severe AD. However, it does not improve day-to-day functioning, quality-of-life measures or rating scores of overall dementia. Rivastigmine is a non-competitive cholinesterase inhibitor. It has been shown to slow the rate of decline in cognitive and global functioning in AD. Galantamine, a reversible and competitive inhibitor of acetylcholinesterase, has also been shown to improve cognitive function significantly and is well tolerated. Adverse effects of cholinesterase inhibitors include nausea, vomiting, diarrhoea, weight loss, agitation, confusion, insomnia, abnormal dreams, muscle cramps, bradycardia, syncope and fatigue. Treatment with these drugs should only be continued in people with dementia who show an improvement or no deterioration in their minimental score, together with evidence of global (functional and behavioural) improvement after first few months of treatment. The treatment effect should then be reviewed critically every 6 months, before a decision to continue drug therapy is made.
Memantine, an N-methyl-d-aspartate (NMDA) antagonist, has also been used for the treatment of moderate to severe AD. It acts mainly on subtypes of glutamate receptors related to memory (i.e. NMDA), resulting in improvements in cognition. It has also been shown to have some beneficial effects on behaviour and its use is recommended in patients with moderate to severe AD as part of well-designed clinical studies (NICE, 2009).
In some studies, donepezil and galantamine have been shown to improve cognition, behaviour and activities of daily living in patients with VaD, and in those with AD and coexistent cerebrovascular disease. Memantine has been reported to stabilise progression of VaD compared with placebo. However, acetylcholinesterase inhibitors and memantine should not be prescribed for the treatment of cognitive decline in patients with VaD, except as part of properly constructed clinical studies (National Collaborating Centre for Mental Health, 2007). Aspirin therapy has also been reported to slow the progression of VaD. The incidence of VaD is likely to decrease with other stroke prevention strategies such as smoking cessation, anticoagulation for atrial fibrillation, control of hypertension and hyperlipidemia.