13.3: Drug Dosing: Geriatric Patients

Elderly individuals encompass a diverse population with varying degrees of age-related physiological changes. Defining the elderly presents challenges, as the geriatric population is often arbitrarily categorized as individuals older than 65. However, many individuals in this group lead active and healthy lives, with an increasing number surpassing 85 years and falling into the older elderly category. Physiological changes associated with aging impact performance capacity and homeostatic reserve, albeit to varying degrees across organs and patients.

Physiological and cognitive functions change during aging, influencing compliance, therapeutic safety, and drug efficacy. The prevalence of multiple drug therapy in the elderly, often due to concomitant illnesses, further complicates medication management. Decreased cognitive function, complex drug schedules, and the high cost of drug therapy can contribute to poor drug compliance, potentially leading to a lack of efficacy, drug interactions, and intoxication.

Vital physiologic functions such as renal plasma flow, glomerular filtration, cardiac output, and breathing capacity exhibit a 10% to 30% decline in elderly subjects compared to those aged 30. These changes necessitate multiple drug therapies for the elderly, potentially resulting in an age-dependent increase in adverse drug reactions or toxicity. This population is more susceptible to cognitive-related adverse events, including confusion, dizziness, delirium, and impaired coordination, especially with drugs that affect the central nervous system. These effects can further compromise safety, increasing the risk of falls, hospitalization, and loss of independence.

The pharmacodynamic hypothesis suggests that age-related alterations in the quantity and quality of target drug receptors may lead to altered drug responses. On the other hand, the pharmacokinetic hypothesis posits that age-dependent increases in adverse drug reactions may stem from physiologic changes in drug absorption, distribution, and elimination, including renal excretion and hepatic clearance.

Furthermore, age-related changes in drug absorption, distribution, and metabolism impact drug responsiveness and clearance in the elderly, potentially affecting drug efficacy and safety. The culmination of these factors underscores the need for comprehensive management and monitoring of medication use in the geriatric population.

The geriatric population is defined as individuals greater than or equal to 65 years.

Aging can impact vital physiological functions, decreasing renal plasma flow, glomerular filtration, cardiac output, and breathing capacity.

It may also alter the quality and quantity of drug receptors, necessitating special considerations when administering drugs to geriatric patients.

Elderly individuals also exhibit decreased lean body mass and increased body fat, which can affect drug distribution.

For instance, water-soluble drugs may exhibit decreased distribution, while lipid-soluble drugs may show increased distribution.

Additionally, the progressive decrease in renal size and function can prolong drug half-lives and reduce drug clearance, necessitating a reduction in the dosage regimen for drugs excreted in the urine.

Also, geriatric patients often have multiple pathophysiological conditions requiring multiple drug therapies, which increases the likelihood of drug interactions and adverse drug reactions.