Table 1.

Specific impacts for different categories of analgesia

Class of drug	Mechanism of action and indication	Common side effects	Considerations in the older person
Paracetamol (acetaminophen)	Inhibits prostaglandin synthesis.	Generally well tolerated with minimal side effects.	Renal impairment: in the older person there is glomerulosclerosis and renal cortical atrophy, consequently, there is a decrease in the glomerular filtration rate (GFR) and a decreased clearance of medications and a reduced renal reserve to recover from nephrotoxic medications. Hepatic impairment: older adults have fewer hepatocytes so there is a decreased hepatic metabolism.
Non-steroidal anti-inflammatory drugs (NSAIDs)	Inhibits cyclooxygenase enzymes.	Gastrointestinal bleeding. Asthma. Renal failure.	Generally avoided in older people who are frail. If used, a short course with a definite stop date is advised. Renal impairment: reduced renal reserves means a higher risk of renal injury; in addition, older adults may be taking a number of other potentially nephrotoxic medications (such as diuretics and ACE inhibitors). The addition of NSAIDs can, therefore, exacerbate existing kidney damage. Gastrointestinal bleeds: NSAIDs can cause gastrointestinal mucosal injury resulting in gastrointestinal bleeding and/or gastritis. Thrombotic events: the risk of thrombotic events is increased in older adults due to the inhibition of substances such as thromboxanae A2, which is an anti-throbotic.
Opioids	Used in conjunction with other analgesia such as paracetamol when these alone have been ineffective. Moderate pain: codeine phosphate and tramadol. Moderate to severe pain: morphine, oxycodone and hydromorphine (causes less pruritus compared with other opioids). Patient-controlled analgesia (PCA) in those who are cognitively intact.	Confusion. Constipation. Respiratory depression.	Certain metabolites within opiates can cross the blood brain barrier resulting in delirium (especially for those with an existing vulnerable brain), respiratory depression and falls. This occurs to a greater extent in older adults. Older adults are more prone to constipation (primarily due to slowed gut transit and medications), which can be exacerbated by opiates. The majority of opioids are renally excreted, therefore, renal changes in the older adult (such as a reduced GFR) can lead to an accumulation of opioids.
Topical analgesia	Capsasin: causes a brief initial sensitisation followed by a prolonged desensitisation of the local pain nerves. Topical NSAIDS eg diclofenac.	Muscle spasms. Palpitations. Peripheral oedema.	The side effects of these medications include localised irritation, erythema and swelling. Topical NSAIDs can cause complications, such as stomach ulcers
Anticonvulsants	Gabapentin and pregabalin: blocks voltage-gated calcium channels. Carbamazepine: blocks voltage-gated sodium channels. All effective for neuropathic pain.	Arthralgia. Confusion. Headache. Drowsiness. Dizziness. Dry mouth.	Through their effects on the central nervous system, anticonvulsants can cause oversedation. There are a number of consequences of this, such as falls and cognitive impairment.
Tricyclic antidepressants (TCAs)	Amitriptyline: blocks noradrenaline and serotonin transporters. Effective for neuropathic pain.	Cardiac arrhythmias. Drowsiness.	Certain considerations in older adults include anticholinergic effects, such as urinary retention, blurred vision and a dry mouth. TCAs can also cause cardiac arrhythmias in various ways, such as blocking noradrenaline reuptake. TCAs can increase intraocular pressure and cause narrow angle glaucoma
Ketamine	Blocks the N-methyl-D-aspartate (NMDA) receptor.	Confusion. Hallucinations.	Ketamine can cause a number of side effects (such as delirium and night terrors) and is rarely used for older adults.
Lignocaine	Hyperpolarisation and decreased excitability of postsynaptic spinal dorsal horn neurones.	Anxiety. Atrioventricular block.	Lignocaine can cause allergic reactions, such as anaphylaxis, nausea, vomiting and changes in heart rate.
Regional anaesthesia	Spinal anaesthesia. Epidural anaesthesia. Nerve blocks along the distribution of the nerve. Helpful perioperatively.	Spinal haematoma. Headache. Infection. Nerve block: bleeding and itching.	Regional anaesthesia can be anatomically challenging to perform in the older adult due to problems such as degenerative bone disease and vertebral joint disease. Both the intervertebral and epidural spaces decrease with ageing along with calcification of the ligamentum flavum.
Duloxetine	This inhibits the reuptake of serotonin and noradrenaline in the central nervous system. Helpful in the treatment of neuropathic pain, such as diabetic neuropathy.	Headache. Diarrhoea. Dry mouth. Insomnia.	Duloxetine is to be used cautiously in the older person as it can cause a number of problems (such as drug-induced movement disorders, confusion and hypertension) due to their noradrenergic effects.