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often associated with higher levels of cognitive function compared with cognitive function if
postoperative pain is undertreated (Lynch et al, 1998; Morrison & Siu, 2000). Herrick at al (Herrick
et al, 1996 Level II) reported no statistically significant difference in the incidence of confusion,
but the rates were 4.3% for patients given fentanyl and 14.3% for those receiving morphine.
Pethidine was associated with a higher incidence of confusion compared with morphine
(Adunsky et al, 2002 Level III‐3) and a variety of other opioids (Morrison et al, 2003 Level III‐2).
Local anaesthetics
Age‐related decreases in clearance of bupivacaine (Veering et al, 1987; Veering et al, 1991) and
ropivacaine (Simon et al, 2006) have been shown. Older patients are more sensitive to the
effects of local anaesthetic agents because of a slowing of conduction velocity in peripheral
nerves and a decrease in the number of neurons in the spinal cord (Sadean & Glass, 2003).
Ketamine
There are no good data on the need or otherwise to alter ketamine doses in the older patient.
In aged animals, however, changes in the composition of the NMDA‐receptor site and function
have been reported (Clayton et al, 2002; Magnusson et al, 2002; Vuyk, 2003). Young and elderly
rats, given the same dose of ketamine on a mg/kg basis showed similar EEG changes but these
changes were quantitatively greater in the older rats (Fu et al, 2008). These data suggest that,
apart from any pharmacokinetic changes, the older person may be more sensitive to the
effects of ketamine and doses may need to be lower in this patient group.
Tricyclic antidepressants
Clearance of tricyclic antidepressant (TCA) drugs may decrease with increasing patient age
and lower initial doses are recommended in older people (Ahmad & Goucke, 2002). Older people
may be particularly prone to the side effects of TCAs (Ahmad & Goucke, 2002; Fine, 2004)
including sedation, confusion, orthostatic hypotension, dry mouth, constipation, urinary
retention and gait disturbances which may increase the risk of falls. Adverse effects appear to
be most common with amitriptyline and nortriptyline may be preferred in this patient group
(Ahmad & Goucke, 2002; Argoff, 2005; McGeeney, 2009). In addition, clinical conditions that may
require TCAs to be administered with caution are more common in older people and include
prostatic hypertrophy, narrow angle glaucoma, CV disease and impaired liver function;
ECG abnormalities may be a contraindication to the use of TCAs in older people (Ahmad &
Goucke, 2002).
Anticonvulsants
As with TCAs, initial doses of anticonvulsant agents should be lower than for younger patients
CHAPTER 11 and any increases in dose should be titrated slowly (Ahmad & Goucke, 2002). As renal function
declines with increasing age, elimination of gabapentin and pregabalin may be reduced and
lower doses will be required (McGeeney, 2009).
The ‘second generation’ drugs such as gabapentin and topiramate may be less likely to result
in adverse effects in the older patient (Argoff, 2005). The relatively high frequency of side
effects such as somnolence and dizziness with pregabalin may be a problem in this group of
patients (Guay, 2005). However, other features of gabapentin and pregabalin, such as a lower
risk of drug‐drug interactions, lower (less than 3%) protein binding, no hepatic metabolism and
the lack of any need to monitor liver function and blood count on a regular basis, means that
these drugs may be well‐suited to the older patient population (McGeeney, 2009).

404 Acute Pain Management: Scientific Evidence