ADVERSE DRUG REACTIONS AND THE ELDERLY

An adverse drug reaction has been defined as ‘any response to a drug which is noxious and unintended and which occurs at doses used in man for prophylaxis, diagnosis or therapy, excluding failure to accomplish the intended purpose’ (1). Adverse drug reactions (ADR) are more common among female patients, particularly those over 60 years of age, among those who take large numbers of drugs (as the elderly often do), and among those who have previously experienced an ADR (2-4). However, the study of ADRs is fraught with difficulties. Whether a symptom is due to administration of a drug or to a patient’s underlying illness needs to be distinguished (1). In addition, many studies of the incidence of ADRs are uncontrolled and fail to consider pretreatment symptoms in the populations examined. This is particularly important because many ADRs mimic non-specific subjective complaints such as dizziness or nausea. Riedenberg et al. (1986) (5) gave a questionnaire, which surveyed symptoms commonly listed as side-effects of drugs, to 414 University students and hospital staff who were taking no medication. Only 19y0 of their subjects had not experienced any of the symptoms in the preceding 72 h; 8% had suffered more than six symptoms. Thus it is essential to compare the symptom profile of a group of patients with that of the population from which it derives. For patients who take several different medications it may prove difficult to identify which causes a particular ADR. Indeed symptoms may be induced by ingesting a tablet rather than the medication it contains. Green (1964) (6) performed a study of three ‘well’ populations: prisoners, hospital staff and their spouses and residents of an elderly person’s home. He recorded symptoms before and after administration of placebo tablets and informed his subjects that new drugs were being studied and side-effects documented. The greatest number and widest variety of symptoms were found among the elderly group: 58% had more than one symptom related to taking the placebo tablet. However, in this group pre-existing complaints were alleviated. Among professionals prior symptoms were compounded by the placebo tablet. When a possible ADR has been identified the next problem is to establish a causeeffect relationship (1). To be ‘definite’ (1) an ADR must be related in time to the administration of a medication (a long interval between exposure to the drug and onset of symptoms may make this difficult), characteristic of the type of drug, resolve on withdrawal of the medication and return on rechallenge (1 , 7). The evaluation of ADRs, based on ‘definite’ events, underestimates their true incidence, whereas ‘probable’ reactions lead to a gross overestimate. Clinical judgement, which decides whether an ADR is definite or not, can vary between doctors. Karch & Lasagna (1977) (8) advocate a more objective assessment of ADRs in response to this problem of definition. They describe an algorithm which analyses each drug reaction systematically, accurately and reproducibly. The decision reached by this method was compared for 63 potential ADRs with the judgement of a group of clinical pharmacologists; both agreed in 45 cases. If