Comprehensive Nursing Pharmacology Q 134
James Perez, a nurse on a geriatric floor, is administering a dose of digoxin to one of his patients. The woman asks why she takes a different pill than her niece, who also has heart trouble. James replies that as people get older, liver and kidney function decline, and if the dose is as high as her niece’s, the drug will tend to:
A. Have a shorter half-life.
B. Accumulate.
C. Have decreased distribution.
D. Have increased absorption.
Correct Answer: B. Accumulate.
The decreased circulation to the kidney and reduced liver function tend to allow drugs to accumulate and have toxic effects. Physiologic changes and disease associated with aging have an impact on pharmacokinetics and pharmacodynamics of medications. Altered drug response and increased adverse reactions are common amongst the elderly. The narrow therapeutic index of digoxin and pharmacokinetic changes associated with aging increases the risk of toxicity. The most important age-related change is that of deterioration of renal function and this is especially true for digoxin where poorer renal excretion demands lower dosage to avoid toxicity.
Option A: Aging results in prolonged elimination half-life and decreased volume of distribution for digoxin [3]. A recent examination of more than 1000 nursing home residents in Canada showed that 32% of elderly heart failure patients are treated with digoxin, 80% of those received doses higher than recommended, serum digoxin levels were higher than toxic levels in 30% of patients, and 26% had other medications known to be a high risk of digoxin interaction prescribed.
Option C: Drug distribution in the older person can vary due to changes in body composition and critical organ perfusion (due to reduced cardiac output and increased peripheral vascular resistance). The latter will also affect metabolism and elimination with decreased liver and kidney perfusion. The reduction in lean body mass in older people (as much as 19%) will cause an elevation in drug concentrations in muscles for drugs distributed in that manner (eg. digoxin).
Option D: With increasing age, the amount of saliva produced is often reduced and this can reduce the rate of drug absorption by influencing the gastric pH. Furthermore, older people have reduced gastric acid secretion and reduced acidity (increased pH) which can delay the dissolution of oral medications. This is exacerbated by delayed gastric empty due to reduced peristaltic force that reduces the mechanical influences on medication mixing with gastric juices. The surface area for drug absorption is also decreased in aging due to intestinal atrophy which, combined with reduced concentration gradient due to the poorer blood flow, inhibits passive diffusion of drugs into the bloodstream further delaying absorption rate.