33: Geriatric Principles

PREVALENCE, LETHALITY, AND UNDERRECOGNITION OF TOXIC EXPOSURE

The population is aging steadily across the world. In the United States, people older than 65 years of age comprise not only an increasing proportion of the population at large (13%) but also an increasing proportion of patients seen in medical practices. Compared with all other age groups, patients older than 65 years of age account for one-fourth of emergency department (ED) ambulance arrivals with the highest proportion of patients in EDs triaged as emergent¹⁰² and the highest number of hospital and intensive care unit admissions.¹¹⁷

Although the elderly account for only a small minority of toxicologic exposures, when exposed, they have a high mortality rate. Among exposures reported to the American Association of Poison Control Centers (AAPCC), the fatality ratio for adults (ie, number of cases divided by number of deaths) exhibits a bimodal pattern, declining after age 30 until age 60, when it again rises (Chap. 136). The factors associated with the increased fatality ratio after age 60 are complex but are likely due in part to physiologic vulnerability.

In a separate study, seven specific pharmaceuticals were selected from the AAPCC database for analysis based on their prevalent use and potential toxicity from 1995 through 2002. These pharmaceuticals were theophylline, digoxin, benzodiazepines, tricyclic antidepressants (TCAs), calcium channel blockers, acetaminophen (APAP), and salicylates.¹¹⁴ The death rate from intentional or unintentional exposure to these pharmaceuticals was found to increase by 35% for each decade of life after age 19 years.¹¹⁴ Although prescribing for some of these drugs has dramatically decreased over time, specific categories continue to pose problems for patients in the latest decades of life.^14,62

Exposures reported to the AAPCC may underestimate the serious consequences for elderly people exposed to xenobiotics that are toxic or potentially toxic. Data from the National Electronic Injury Surveillance System–Cooperative Adverse Drug Event Surveillance Project (NEISS-CADES) indicate that patients aged 65 years and older accounted for 25% of estimated visits related to adverse drug events (ADEs) and almost 50% of such visits requiring hospitalization or prolonged monitoring in the ED during 2004–2005.¹⁵ Furthermore, the incidence of ADEs increases steeply from age 65 years through the tenth decade of life.¹⁵ More recent NEISS-CADES data indicate that almost 50% of elders who required emergency hospitalization as a result of ADEs are people 80 years of age or older.¹⁴ The problem may be even greater than the NEISS-CADES study suggests, because their data did not capture ADEs in patients treated or dying outside of EDs, ADEs that could only have been recognized after admission, or ADEs that might be erroneously diagnosed as non–drug-related problems.

Toxic exposures in the elderly may be underrecognized for several reasons. First, because of pharmacokinetic and pharmacodynamic changes that occur with aging,³³ which a “standard” therapeutic dose may produce as an unexpected serious effect. ...