Br J Clin Pharmacol 1998; 46: 531–533

Prescribing for the elderly patient: why do we need to exercise caution?

S. G. HughesDivision of Geriatrics, St George’s Hospital Medical School, Blackshaw Road, London SW17

age [5] but this may reflect poor nutrition, chronic illnessIntroduction

or debility rather than the effects of the ageing process itselfand for the vast majority of drugs any changes in proteinAdvancing age is accompanied by pharmacokinetic and

pharmacodynamic changes which, together with impairment binding which do occur are not clinically significant.However, in the case of extensively bound drugs just a smallof homeostatic mechanisms and the effect of coexisting

disease, contribute to a significant increase in sensitivity to reduction in protein binding may result in a clinicallysignificant increase in free drug concentration. Drugs whoseparticular drugs and a corresponding increase in the incidence

of adverse drug reactions (ADRs). Increasing medical reduced protein binding in elderly people may result inadverse reactions include warfarin, tolbutamide, phenytoinawareness of these facts has not universally been translated

into clinical practice as polypharmacy remains a particular and salicylic acid. Coexisting disease (the incidence of whichincreases with age) may have a more profound effect onproblem amongst elderly people and the degree of polyphar-

macy increases with advancing age [1, 2]. Such prescribing serum albumin concentration than age alone and maytherefore alter the pharmacokinetics of an even wider rangepractice serves to further elevate the risk of drug interactions

and ADRs, both directly via the synergistic or antagonistic of protein bound drugs.actions of coprescribed drugs, and indirectly by increasingthe likelihood of failed compliance.

Elimination

Elimination of most drugs occurs via metabolism in thePharmacokinetics

liver and/or excretion by the kidneys.Pharmacokinetics comprises drug absorption, distributionand elimination. Metabolism

Hepatic metabolism comprises phase 1 reactions (oxidation,Absorption reduction and hydroxylation, largely performed by the

mixed function oxidases such as cytochrome P450) andNumerous gastrointestinal changes occur with age, e.g.phase 2 reactions (conjugation with glucuronate, sulphateincreased gastric pH, delayed gastric emptying, decreasedor acetate). Phase 2 reactions usually involve conjugation ofintestinal motility and decreased splanchnic blood flow, butphase 1 metabolites and appear to be unchanged by thesurprisingly drug absorption changes very little [3]. However,ageing process although they may impaired in some frailthe fact that older patients are often taking severalelderly people [6, 7]. Phase 1 reactions however, aremedications concurrently (both prescribed and over-the-reduced, probably due to a combination of reduced hepaticcounter preparations) means that it is particularly importantblood flow (35% reduction in hepatic blood flow in theto consider the effects of any coprescribed drugs onelderly) and reduced hepatic volume (hepatic volume isabsorption. For example antacids or bile acid sequestrantsreduced by 28% in men and 44% in women by the age ofmay reduce the absorption of certain drugs.91) [8]. The result is that drug metabolism, particularly first-pass metabolism (e.g. propranolol, labetalol, verapamil,

Distribution metoclopramide, opioids) may be considerably reduced inelderly people. In addition many other factors includingAgeing is accompanied by an increase in body fat, a decreasesmoking, alcohol consumption, coexisting diseases andin lean body mass and a decrease in total body water [4].certain drugs (e.g. erythromycin, amiodarone) can alsoSince drug distribution depends largely on body compositioninhibit hepatic enzymes and so impair drug metabolismthese changes result in reduced volume of distribution ofstill further.water soluble drugs, e.g. digoxin (which may lead to

increased initial drug concentration) and increased volumeof distribution of lipid soluble drugs, e.g. benzodiazepines Excretion(which may lead to increased elimination half-life and

Ageing is accompanied by a number of renal changes [9,prolonged effect). Both types of drug may therefore require10] These include both reduced glomerular function (GFRreduction in dose and/or dose interval. Drug distribution isis reduced by 6 to 10% per decade after the age of 40 [11]also affected by binding to plasma proteins, with highlyand reduced tubular function which means that by the ageplasma protein bound drugs tending to have a low volumeof 90 there may be a 30 to 40% reduction in overall renalof distribution (the converse is true for poorly bound drugs).function. This results in reduced clearance of both drugsSerum albumin levels have been reported to reduce withwhich are mainly excreted via filtration at the kidney, e.g.digoxin and of drugs which are actively secreted by therenal tubules e.g. penicillin. Dose reduction may thereforeCorrespondence: Dr S. G. Hughes, Division of Geriatrics, St George’s Hospital

Medical School, Blackshaw Road, London SW17. be required when prescribing such drugs for older patients.

© 1998 Blackwell Science Ltd 531

S. G. Hughes

Renal function may also be adversely affected by the Congestive cardiac failure results in reduced absorption(due to mucosal oedema, reduced epithelial blood supplypresence of coexisting disease e.g. hypertension, diabetes,

congestive cardiac failure, or acute illness such as urinary and splanchnic vasoconstriction), reduced volume of distri-bution (due to decreased tissue perfusion) and reducedtract infection and dehydration, all of which are common

in elderly people. elimination (due to reduced hepatic blood flow, reducedoxidising capacity as a result of hypoxia, reduced GFR andincreased tubular reabsorption).

Pharmacodynamics

Pharmacodynamics concerns drug action and side effects.PolypharmacyThe pharmacodynamic changes that occur with ageing are

complex and have not been well characterised in humans.Polypharmacy results in both increased likelihood of drug

They depend upon both receptor density, signal transductioninteractions/ADRs and increased tendency to mistakes in

(e.g. via cyclic AMP in the case of b-adrenergic receptors)drug compliance. Elderly people constitute the major

and intracellular response (e.g. biochemical changes orconsumers of prescribed medications in this country with

induction of protein transcription). They may also beabout 70% receiving prescribed drugs. Consequently many

affected by diet [12] Reported changes that occur withsurveys of prescribing patterns in elderly people have been

ageing include increased response (i.e. sensitivity) to warfarin,performed with the fairly unanimous conclusion that

benzodiazepines and opiates and reduced inotropic andpolypharmacy is more common in older people and that

chronotropic responses to b1-adrenergic stimulation [13, 14].the degree of polypharmacy increases with advancing ageof the patient [2]. One might argue that this trend is

Adverse drug reactions expected due to the fact that the incidence of chronicdisease and hence subsequent treatment increases with age.

ADRs increase steadily in incidence with age [15] and areHowever the fact remains that many elderly patients are on

three times more common in those over 90 years than inunnecessary medications and evidence suggests that

those under 50. This is due not only to pharmacokineticinfrequent review of patient medication may be a major

and pharmacodynamic changes but also to impairment ofcontributing factor. For example one community survey of

homeostatic mechanisms. Those mechanisms that are par-elderly people found that 59% of drugs had been prescribed

ticularly affected by ageing include baroreceptor responses,for more than 2 years and 32% for more than 5 years, the

control of body sway, thirst, volume regulation, glucose andvast majority (88%) were issued by repeat prescription and

electrolyte control, and thermoregulation. It is therefore not40% of the patients had not discussed their treatment with

surprising that elderly people are particularly sensitive toa doctor in the previous 6 months [20].

drugs which may cause, respectively, postural hypotension(e.g. antihypertensive or antiparkinsonian medication), ataxia(e.g. benzodiazepines), volume depletion and electrolyte

Complianceimbalance (e.g. diuretics) or hypothermia (e.g. phenothiaz-ines). The scale of the problem is illustrated by the results Contrary to popular belief an elderly person whose mental

function is intact is no more likely to make mistakes withof studies which show that 10% or more of elderly patientadmissions are due to ADRs [16, 17]. Even in hospitalized their medication than a younger person. However polyphar-

macy does make such errors more likely: in one study thepatients the incidence of ADRs is in the order of 15% [18].These are usually type A (dose related) rather than type B incidence of mistakes increased 15-fold when the number

of drugs prescribed was increased from 1 to 4 [21].(idiosyncratic) which implies that they are largely prevent-able. Lindley et al. found that 50% of cases were actually Consequently accidental errors in drug compliance are very

common in elderly people and some of these errors maydue to inappropriate prescribing [19].actually be due to oversights on part of the doctor orpharmacist, for example a patient with arthritic hands may

Coexisting diseasehave difficulty in removing child-proof caps or a patientwith poor eyesight may not be able to read the instructionsThe incidence of chronic disease increases with age and

some diseases can have profound effects on pharmacokinetics, on the drug bottle.Deliberate non-compliance is also a major problempharmacodynamics and sensitivity to certain drugs. Renal

impairment and congestive cardiac failure are particularly although not one that is specific to elderly people. It maytake the form of failing to take prescribed medication ascommon in elderly people and are discussed below.

Renal failure results in reduced secretion of drugs which frequently as directed; taking a larger dose in the mistakenbelief that it will be more therapeutic or lead to a fasterare mainly eliminated via the kidneys resulting in both

accumulation of the drug and increased length of time to cure; hoarding drugs for future unauthorised use, or self-prescribing with over-the-counter preparations (OTCs). Thereach steady state plasma levels (takes approximately 5 half-

lives). In addition subtle changes in the structure of albumin causes of deliberate non-compliance are multifactorial butcontributing factors include ADRs, inconvenience of takingmay result in reduced binding of acidic drugs leading to

increased unbound (i.e. biologically active) drug. Increased medication and differing perceptions of what is importantby doctor and patient.meningeal permeability can result in increased sensitivity to

certain drugs e.g. opiates, barbiturates, phenothiazines, More detailed reviews of compliance in elderly peoplehave been published elsewhere [22, 23].benzodiazepines.

© 1998 Blackwell Science Ltd Br J Clin Pharmacol, 46, 531–533532

Prescribing for the elderly patient

5 Greenblatt DJ. Reduced serum albumin concentration in theConclusion elderly: a report for the Boston Collaborative Drug

Surveillance Program. J Am Geriatr Soc 1979; 27: 20–22.The pharmacokinetic, pharmacodynamic and homeostatic6 Wynne HA, Cope LH, Herd B, Rawlins MD, James OF,changes that occur with age combine with the effects of

Woodhouse KW. The association of age and frailty withchronic disease to make the elderly person particularlyparacetamol conjugation in man. Age & Ageing 1990; 19:

sensitive to both the desired and adverse effects of many 419–424.drugs. This is compounded by an increase in both the 7 Wynne HA, Yelland C, Cope LH, Boddy A, Woodhouseincidence and degree of polypharmacy. The result is that KW, Bateman DN. The association of age and frailty withboth ADRs and poor compliance are particularly common the pharmacokinetics and pharmacodynamics ofin elderly people. metoclopramide. Age & Ageing 1993; 22: 354–359.

8 Woodhouse KW, James OFW. Hepatic drug metabolism andA rational approach to prescribing for elderly people isageing, Br Med Bull 1990; 46: 22–35.therefore essential, particularly in the current climate where

9 Miller M. Fluid and electrolyte homeostasis in the elderly:an increasing number of drugs are becoming available asphysiological changes of ageing and clinical consequences.OTCs. It is our responsibility, as medical practitioners, toBailliere’s Clinical Endocrinology & Metabolism 1997; 11:minimize polypharmacy; to simplify drug regimens as much367–387.

as possible (e.g. by using once daily or combined preparations10 Fliser D, Ritz E. Renal haemodynamics in the elderly.

wherever possible); to pay attention to the correct dose Nephrology, Dialysis, Transplantation 1996; 11(Suppl 9): 2–8.and/or dose interval; to consider possible drug interactions, 11 Davies D F, Shock N W. Age changes in GFR, effect ofand to communicate effectively with our patients in terms renal plasma flow and tubular excretory capacity in adultthat they will understand. We should provide patients with males. J Clin Invest 1950; 29: 496–507.

12 Feldman RD. A low sodium diet corrects the defect in betaclear and simple instructions about how much, how oftenadrenergic response in older subjects. Circulation 1992; 85:and for how long they should take each of their medications612–618.and ensure that the patient knows exactly why he takes each

13 Scarpace P, Tumer N, Mader S. Beta adrenergic function inof his drugs, the importance of taking these medications atageing: basic mechanisms and clinical implications. Drugs andthe correct times and the importance of continuing treatmentAging 1991; 141: 116–129.uninterrupted. Suggested guidelines to aid rational prescrib-

14 White M, Roden R, Minobe W, Khan M F, Larrabee P,ing for elderly people are shown below Wollmering M et al. Age-related changes in beta-adrenergic

neuroeffector systems in the human heart. Circulation 1994;90: 1225–1238.

Guidelines for Prescribing for Older People15 Walker J, Wynne H. Review: the frequency and severity of

adverse drug reactions in elderly people. Age & Ageing 1994;(adapted from Walley & Scott, 1995) [24]23: 255–259.1 Appropriate treatment requires adequate clinical assess-

16 Williamson J, Chopin JM. Adverse drug reactions toment and accurate diagnosisprescribed drugs in the elderly: a multicentre investigation.2 Problem orientated prescribing, i.e. treat only theAge and Ageing 1980; 9: 73–80.

disorders that need to be treated17 Cunningham G, Dodd TR, Grant DJ, McMurdo ME,

3 Keep drug regimens simple Richards RM. Drug-related problems in elderly patients4 Use low doses and increase slowly admitted to Tayside hospitals, methods for prevention and5 Avoid polypharmacy subsequent re assessment. Age & Ageing 1997; 26: 375–382.6 Consider potential drug interactions 18 Gray SL, Sager M, Lestico MR, Jalaludin M. Adverse drug

events in hospitalized elderly. Journals of Gerontology Series A,7 Provide patient with clear instructions, both verbal andBiological Sciences & Medical Sciences 1998; 53: M59–63.in writing

19 Lindley CM, Tully MP, Paramsothy V, Tallis RC.8 Review patients and their medications regularlyInappropriate medication is a major cause of adverse drug9 If in doubt, don’t prescribereactions in elderly patients. Age & Ageing 1992; 21: 294–300.

20 Cartwright A, Smith C. Elderly people: their medicines and theirdoctors. London: Routledge, 1988.References

21 Parkin DM, Henney CR, Quirk, Crooks J. Deviation from1 Griffin JP, Chew R. Trends in the usage of prescription medicines prescribed drug treatment after discharge from hospital.

by the elderly and very elderly between 1977 and 1988. London: Br Med J 1976; 2: 686–688.Association of the British Pharmaceutical Industry, 1990. 22 Stewart R B. Noncompliance in the elderly: is there a cure?

2 Purves I, Kenny J. The quality of general practice repeat Drugs & Aging 1991; 1: 163–167.prescribing. University of Newcastle upon Tyne: Dept of 23 Hughes S. Compliance with drug treatment in the elderly.Primary Health Care, 1994. Prescriber 1998; 9: 45–54.

3 Bender AD. The effect of age on intestinal absorption: 24 Walley T, Scott AK. Prescribing in the elderly. Postgrad Med Jimplications for drug absorption in the elderly. J Am Geriatr 1995; 71: 466–471.Soc 1968; 16: 1331–1339.

4 Greenblatt DJ, Sellers EM, Shader RI. Drug disposition in old (Received 25 February 1998,accepted 16 July 1998 )age. N Engl J Med 1982; 306: 1081–1088.

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