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Prescribing for older patients offers special challenges. Older people take about three times as many prescription medications as do younger people, mainly because of an increased prevalence of chronic medical conditions among the older patient population. Taking several drugs together substantially increases the risk of drug interactions and adverse events. Many medications need to be used with special caution because of age-related changes in pharmacokinetics (i.e., absorption, distribution, metabolism, and excretion) and pharmacodynamics (see Chapter 8). For some drugs, an increase in the volume of distribution (e.g., diazepam) or a reduction in drug clearance (e.g., lithium) may lead to higher plasma concentrations in older patients than it does in younger patients. Pharmacodynamic changes with aging may result in an increased sensitivity to the effects of certain drugs, such as opioids, for any given plasma concentration. The pharmacokinetic and pharmacodynamic changes with aging are discussed in Chapter 8.

While a physician can usually do little to alter the characteristics of individual older patients to affect the kinetics or dynamics of drugs, the decision whether to prescribe any drug, the choice of drug, and the manner in which it is to be used (e.g., dose and duration of therapy) are all factors that are under control of the prescriber. This chapter discusses ways to optimize prescribing of drug therapy for older adults.

Writing a prescription is the most frequently employed medical intervention. Yet, creating optimal drug regimens that meet the complex needs of older persons requires thought and careful planning. Multiple factors contribute to inappropriate drug prescribing, including lack of adequate training of doctors in safe prescribing behavior and in prescribing for geriatric patients. Further, a lack of a routine use of safe medication prescribing behaviors such as checking drug allergies, double checking drug doses, adjusting doses for renal impairment, and potential drug–drug interactions also contribute to prescribing errors. Avoidable adverse drug events (ADEs) are the most serious consequences of inappropriate drug prescribing. The possibility of an ADE should always be borne in mind when evaluating an elderly individual. A maxim from one wise geriatrician recommends: “In evaluating virtually any symptom in an older patient, the possibility of an ADE should be considered in the differential diagnosis.” Advanced age, frailty, and increased drug utilization are all factors that contribute to an individual patient's risk for developing a drug-related problem. In the ambulatory setting, 25% of patients may have ADEs. When an ADE is identified in the ambulatory setting between 11% and approximately 25% are considered to be preventable. In the nursing home setting, the incidence is higher and approaches 10 ADEs per 100 resident-months, of which over half were preventable. These estimates are probably low because preventable ADEs were strictly defined and assumed that, in many cases, the prescription of the offending drug was indicated and the ADE was therefore not preventable. As many as 28% of hospital admissions among older patients result from drug-related problems. Up to 70% of these ...

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