Fundamental Considerations
- Recognize that presenting features of disease/illness may be different and
having a greater awareness of the impact of chronic illness on the patient.
- Perspective is different than with younger adults.
Physiological Changes with Aging
- The clinician must be aware that all the systems interact an, in doing so, can
increase the older person’s vulnerability to illness/disease.
- During the clinical decision-making process, the clinician knowledgeable about
physiological changes with aging will be less likely to undertreat a treatable
condition. -Example- Use the diagnostic process to differentiate the more benign
seborrheic keratosis from actinic keratosis.
- Be informed; do not attribute a finding to the aging process alone. The elder may
conclude there is no point in changing behavior, because the process is inevitable.
- Three primary points:
1) There is a reduced physiological reserve of most body systems, particularly
cardiac, respiratory, and renal.
2) There are reduced homeostatic mechanisms that fail to adjust regulatory
systems such as temperature control and fluid and electrolyte balance.
3) There is impaired immunological function: infection risk is greater, and
autoimmune diseases are more prevalent.
Laboratory Values in Older Adults
- Many factors can influence lab value interpretation in the elderly, including the
physiological changes with aging, the prevalence of chronic disease, changes in
,nutritional and fluid intake, lifestyle (including activity), and the medications
taken.
- Reference ranges therefore may be preferable. Reference ranges or intervals,
such as age, sex, or race can be defined demographically. For example, the
reference range for older adults might be the intervals within which 95% of
persons over age 70 fall.
- Further defined physiologically (fasting or activity status) or pharmacologically
(medication, tobacco or ETOH use).
- Biochemical individuality is of particular importance in detecting asymptomatic
abnormalities in older adults. Significant homeostatic disturbances in the same
individual may be detected through serial laboratory tests, even though all
individual test results may lie within normal limits of the reference interval for the
entire group.
- The clinician must determine whether a value obtained reflects a normal aging
change, a disease, or the potential for disease.
- Misinterpretation of an abnormal lab value as an aging change can lead to
underdiagnosis and undertreatment in other (anemia or UTI) and overdiagnosis
and overtreatment in others (hyperglycemia or asymptomatic bacteriuria).
- At times, the result of a lab value may be within the appropriate reference range
yet indicate pathology for the older adult.
- Calculation of creatinine clearance is important in the estimation of renal
function.
- Reduced renal function, particularly GFR, affects clearance of many drugs, and
creat clearance provides an index of renal function for use in choosing doses of
renally eliminated or nephrotoxic drugs (such as dig, H2 blocker, lithium, and
water soluble antibiotics)
- The Modiciation of Diet in Renal Disease (MDRD) and Cockcroft-Gault equations
both provide useful estimates of the GFR.
- Any risks involved in lab testing must be considered with respect to the patient’s
clinical condition and weighed against the test’s expected benefits.
Pharmacokinetic & Pharmacodynamic Changes
, - Polypharmacy and the potential for an adverse drug reaction (ADR) are major
concerns in elders.
- Polypharmacy primary predictor for an ADR (any unwanted response).
- The therapeutic window narrows with age. The potential for benefiting the
patient measured against risk of doing harm important.
- Pharmacokinetics (what the body does to the drug) and pharmacodynamics
(what the drug does to the body) alter the dynamic processes that drugs undergo
to produce therapeutic effect due to the effects of the aging process.
Absorption
- Less impact than distribution, metabolism, elimination.
- Gastric acidity declines with age; offset by the longer contact time that occurs as
transit time slows – which is more functional than physiological.
- Presence of food and other drugs in the stomach at the same time affect drug
absorption.
- Antacids and Fe can inhibit absorption.
- Anticholinergic meds cause a slowing of colonic motility and can result in greater
absorption rates.
- Metabolic diseases, such as thyroid disease/DM can increase or decrease transit
time, can cause either increased/decreased drug absorption.
- When the med passes through the esophagus without adequate water, can
cause erosion.
Distribution
- Drug distribution is affected by aging, particularly in individuals of smaller body
size, decreased body water, higher body fat.
- Drugs distributed in water have a higher concentration in elders, and exert a
more profound effect.
- Drugs distributed fat have a wider distribution and a lesss intense effect but a
more prolonged action, particularly with more adipose tissue.
- Drugs with a high protein binding rate have a greater potential to cause an ADR
in those with less body mass. Fewer receptor sites, less albumin for binding,
greater plasma concentration, more free drug is available for processes.
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