Medication Prescribing for Older Adults
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INTRODUCTION
Persons over age 65 represent about 12% of the population, yet they receive over 25% of all prescribed drugs in the United States.1 One national survey showed that 50% of community-dwelling elderly over age 65 used five or more prescription and over-the-counter (OTC) medications per week, and 12% used 10 or more.2 Thirty percent of hospital admissions in elderly patients can be linked to adverse drug events, defined as “noxious and unintended patient events (ie, symptoms, signs, and laboratory abnormalities) caused by a drug.” The most common cause of adverse drug events is inappropriate medication prescribing.3
Medications are deemed to be inappropriate if they pose more risk than benefit to the individual. The risk of adverse drug events resulting from inappropriate medication prescribing range from weakness, to falls and fractures, to even life-threatening events.4,5 Studies show prevalence of at least one inappropriate medication being prescribed for up to 40% of nursing home residents and 21% of community-dwelling elderly.6
Underprescribing of medically indicated drugs such as low-dose aspirin can also place a person at risk. Suboptimal prescribing has been shown to adversely impact outcomes for many diagnoses, including cardiovascular disease, stroke prevention, and osteoporosis prevention.7-9 Underuse of medications can result from fear of prescribing a medication that might lead to adverse events, attempts to prevent polypharmacy, economic barriers, or lack of patient adherence to medications.10 Thus, providers must balance the pros and cons of each medication that they prescribe for their older patients.
Achieving adherence to needed medications can be challenging.11 Factors affecting adherence that are disproportionately represented in the elderly include polypharmacy, polydosing, cognitive deficits, and impaired physical function. Lack of adherence to prescribed medicines increases the likelihood of an adverse outcome, including treatment failure, medication overdose, and avoidable hospitalization.12
PHYSIOLOGIC CHANGES WITH AGING
Pharmacokinetics refers to drug absorption, distribution, metabolism, and elimination. While drug absorption is typically slowed but complete in the elderly, aging has profound affects on distribution, metabolism, and excretion of drugs. Volume of distribution of medications is decreased by the reduced muscle mass and total body water typical of aging. As a result, medications will attain higher plasma concentrations if they distribute into muscle or total body water. This is particularly important for medications that require loading doses. Another typical change with aging is increased fat mass, which acts as a depot for lipophilic drugs such as benzodiazepines and amiodarone.13
Drug potency and duration of action are often increased in the elderly due to decreased renal and hepatic function. The Cockroft-Gault formula should be used to estimate creatinine clearance in older adults when prescribing a new medication or when changing doses:
Creatinine clearance = (140-age) x weight (kg) (x 0.85 for women
72 x serum creatinine
Serum creatinine does not accurately reflect renal function in older persons because of decreased lean body mass.14
COMMON CHARACTERISTICS OF OLDER ADULTS WITH MEDICATION-RELATED PROBLEMS
In addition to physiologic changes of aging, the accumulation of medical diagnoses also contributes to medication-related problems. Certain patient characteristics should prompt the provider to pay special attention to potential prescribing problems.
References
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