An older adult patient presents with signs and symptoms related to drug toxicity. Which age-related change may have contributed to this problem?

Choice A reason: A reduced adipose-to-lean body mass ratio increases drug distribution for lipophilic drugs, but this is less relevant for most toxicities. In older adults, fat increases relative to lean mass, altering drug distribution, but renal clearance is a more significant factor in drug accumulation and toxicity. Choice B reason: Decreased renal blood flow in older adults reduces glomerular filtration rate, impairing drug excretion. This leads to accumulation of renally cleared medications, increasing toxicity risk. Aging kidneys have reduced nephron function, prolonging drug half-life, making this a primary contributor to drug toxicity in this population. Choice C reason: Elevated total body water is not typical in older adults, who have reduced body water. This affects water-soluble drug distribution but is less critical than renal impairment. Decreased renal function is a more direct cause of drug accumulation, making this choice incorrect for toxicity. Choice D reason: Gastrointestinal absorption does not significantly increase in older adults; it may decrease due to reduced gastric motility or acid production. Drug toxicity is more commonly caused by impaired renal clearance than enhanced absorption, as the kidneys’ reduced function leads to drug accumulation and adverse effects.