In older adults, decreased GFR leads to which pharmacokinetic change?

• A. Increased drug clearance and shorter half-life.
• B. Reduced drug clearance and prolonged half-life; increased toxicity risk.
• C. No change in pharmacokinetics.
• D. Only hepatic metabolism is affected.

Answer: (B)

As people age, kidney function typically declines, lowering the glomerular filtration rate. This directly reduces the body's ability to clear drugs that are eliminated renally. When clearance drops, the elimination half-life lengthens (t1/2 = 0.693 × Vd / Cl), so the drug stays in the body longer and can accumulate with repeated dosing. That accumulation raises the risk of toxicity, especially for drugs with a narrow therapeutic range.

So the situation described—decreased GFR leading to reduced drug clearance and a longer half-life, with increased toxicity risk—fits the pharmacokinetic changes seen in older adults. The other statements don’t align with renal elimination: clearance wouldn’t increase, there wouldn’t be no change, and the idea that only hepatic metabolism is affected ignores the impact of reduced GFR on renal clearance.