Mohammed T. Abou-Saleh

614 PRINCIPLES AND PRACTICE OF GERIATRIC PSYCHIATRYfiltration rates fall steadily in old age, leading to the accumulationof renally excreted drugs. This may be compounded by renaldamage due to drug misuse, e.g. analgesic abuse 11 . Hepaticmetabolism is impaired due to a loss of liver mass and a reducedblood flow, which may also be compounded by toxic drug effects,such as alcohol leading to fatty liver. The efficiency of microsomaloxidation also falls with age, leading to reduced drug excretion ofhepatically metabolized drugs 12 . The combination of these effectsmay greatly alter pharmacokinetics in the elderly. For example,Klotz estimated the half-life of diazepam in the very elderly to beover 3 days, compared with 20 h in a younger subject 13 .Multiple drug use increases the difficulty of prediction of thebehaviour pattern of an individual substance, due to competitionfor binding sites and metabolic pathways. Polypharmacy mayhave different effects, depending on whether it is acute or chronic.Alcohol will inhibit microsomal enzyme activity in acute use,while prolonged administration will induce the same enzymes.Hence, alcohol will acutely raise concentrations of benzodiazepines,while lowering them if used chronically 14 .Pharmacodynamics also alter in the elderly. Sensitivity todrugs, particularly those acting on the central nervous system,tends to increase, while drug receptor populations also changewith increased age. The particular effect of the changes depends inpart upon whether the receptor involved is facilitatory orinhibitory.As a consequence of all these variables, the prediction of adrug’s effects in the elderly, based on observation of its effects onyounger adults, is foolhardy. Similarly rigid application ofrecommended ‘‘safe levels’’ of substance use, such as those issuedby the Department of Health in the UK, may result in falsereassurance to clinicians and patients with a consequent failure toidentify cases of harmful use in the elderly.CONCLUSIONThe terms ‘‘old age’’ and ‘‘substance misuse’’ are both terms thathave a wide range of meaning to different readers. The currentliterature is based primarily upon chronological age banding ofindividuals, as opposed to banding by overall health, possibly amore valid measure. Definitions of substance misuse are similarlyvaried. Often in transgenerational studies definitions of casenessare set at a level to prevent false-positive reports for youngeradults. In older age groups, where less of a substance may have agreater effect, there is the possibility of missing cases if suchstandards are applied. The greater likelihood of drug interactionsin the elderly should be considered when determining thedependency potential of any given drug or medication.PREVALENCE AND CORRELATESThe elderly may display harmful use of any psychoactivesubstance. Misuse of alcohol, opioids, cannabinoids, sedatives,stimulants, hallucinogens and tobacco are all reported among theelderly. However, access to a potential substance of abuse is keyto determining what an individual may misuse. Alcohol isobtainable with ease in most industrialized nations and is asocially acceptable and accessible psychoactive drug. Amongst theelderly, ill-health is common. Sedatives, hypnotics and analgesicsare easily accessible through prescription and consequently, alongwith alcohol, are responsible for the majority of cases of harmfuluse. Over-the-counter medication is also easily obtained and maybe misused. Illicit drugs are usually only available in potentiallydangerous environments from individuals who may pose asignificant risk to vulnerable older adults. Illicit drug use is notcommonly observed in the elderly.BENZODIAZEPINESBenzodiazepines replaced barbiturates as the mainstay ofpharmacological interventions in both anxiety and sleep disturbance.They maintain their relative dominance in this field despitethe recent development of newer drugs with reportedly lessaddictive potential. Benzodiazepines accumulate more readily inthe elderly due to changes in body composition, leading to agreater volume of distribution for lipophilic drugs. Chronic usemay contribute to toxic effects, including cognitive impairment,poor attention and anterograde amnesia, cerebellar signs such asataxia, dysarthria, tremor, impaired coordination and drowsiness39 . Increased falls and hip fractures are associated withbenzodiazepine use 40, , whilst withdrawal may be accompanied byrebound insomnia, agitation, convulsions and an acute confusionalstate. If benzodiazepines are required then short-term useof low doses of short- or medium-acting drugs is advised. There isno ‘‘safe’’ period of use but tolerance and dependence levelsincrease with prolonged use 41 .Prevalence of Benzodiazepine UseEstablishing levels of benzodiazepine use is subject to the samedifficulties as establishing alcohol use except where it is aprescription medication, when some idea of identity and demographiccharacteristics of the potential user should be available. Inareas where benzodiazepines are available over the counter, thenature of users and misusers is harder to establish. Nationalprescription audits can reflect trends in use but are unhelpful whenconsidering particular population subgroups. Prescribing ofbenzodiazepines in England and Wales has fallen from 20.6million prescriptions in 1987 to 13.9 million in 1996 42 , a fall of32%. In England in 1996, 55% of prescriptions for benzodiazepineswere issued to patients over the age of 60. Many of theseprescriptions were issued to long-term users. A recent communityfollow-up study of 5000 over-65s in Manchester 43 revealed that10% were using benzodiazepines on first assessment and that ofthese some 70% were taking a benzodiazepine 2 years later. Afurther 4 year follow-up revealed that 69% of these were still onbenzodiazepines. Patients entering the study on benzodiazepineshad a 52% chance of taking benzodiazepines throughout the4 year period. Women were twice as likely to be taking abenzodiazepine as men at any stage in the study. In the USA, astudy found 6.3% of a large sample of over-65s used a hypnotic,one-third of these daily and nine-tenths for at least 1 year 44 . Fiveyear follow-up found 46.6% still using hypnotics, but with aswitch away from barbiturates and longer-acting benzodiazepinestowards short-acting ones 45 .Use of benzodiazepines in institutional samples has traditionallybeen higher and associated with female gender, greater age,bereavement and poor health 46 . In the USA it has been shownthat one-fifth of nursing-home residents were taking potentiallyaddictive drugs on a daily basis. The medication in question isusually a benzodiazepine 47 . Studies from other countries revealsimilarly high levels of benzodiazepine use among institutionalizedolder adults 48 . The level of morbidity among institutionalresidents is likely to be higher than community-dwelling elders. Itis unclear whether this morbidity is sufficient to explain a doublingin levels of use of benzodiazepines in this group. While chronicpain may require treatment with dependence-inducing medication,there are few indications for long-term benzodiazepine use.It has been argued that the regular use of benzodiazepines ininstitutions is a form of behavioural control, used more for thebenefit of staff and others than these users. In many cases, theindividual may be incapable of giving valid consent to taking suchmedication. The use of medication in such circumstances may be