A hallmark of aging in humans is the development of multiple, coexisting physiological and pathophysi-ological changes that may benefit from drug therapy. It is not uncommon for the older individual to have 5 to 10 diagnoses, each of which has one or more proved beneficial therapies (Table 24.1). Examples abound: hypertension, coronary artery disease, osteoarthritis, osteoporosis, type 2 diabetes mellitus, and treated prostate or breast cancer often coexist in an individual patient. In addition, treatable insomnia, depression, and anxiety may be present, either independently or associated with primary medical illnesses. As the number of individuals who are greater than 85 years old dramatically increases, the incidence of Alzheimer's disease and other forms of cognitive impairment for which somewhat effective treatment is available will increase as well (Figure 24.1). This will increase medication exposure and the potential for drug interactions (see Chapter 15) even more. With the availability of medications that are in many instances dramatically effective, it is imperative to understand the impact of multiple current medications (high drug burden) on the older individual.
A number of studies over the past three decades have demonstrated that the likelihood of adverse drug effect increases with the number of drugs prescribed (1,2). There is a disproportionate increase in both total and severe adverse drug reactions when more than five drugs are coadministered (3). Adverse drug effects also are more likely in older patients when certain drugs, such as warfarin, theophylline, or digoxin, are among the drugs prescribed. However, the absolute number of drugs the patient concurrently receives is probably the best predictor of an adverse drug event (Figure 24.2) (2).
Further complicating this issue is the fact that the relative therapeutic benefit of treatments such as thrombolytic therapy, hypocholesterolemic therapy, postmyocardial infarction b-locker treatment, and angiotensin-converting enzyme inhibitor treatment in congestive heart failure in patients over the age of 75 is similar to that seen in younger patients. Unfortunately, these data create a dilemma in that dramatic therapeutic advances have been made for many illnesses that afflict the elderly, yet administration of multiple medications increases the likelihood of adverse drug events.
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