In older adults with decreased renal function, what is the likely effect on drug half-life?

• A. The half-life increases
• B. The half-life decreases
• C. No change
• D. Unpredictable

Answer: (A)

Renal clearance governs how quickly a drug is removed from the body. In older adults, decreased kidney function lowers the glomerular filtration rate, so the body clears drugs more slowly. The half-life of a drug depends on how quickly it’s eliminated (t1/2 ≈ 0.693 × Vd / CL). When clearance (CL) drops due to reduced renal function, the half-life increases. That means renally cleared drugs stay in the body longer, raising the risk of accumulation and toxicity unless the dose or dosing interval is adjusted. So the likely effect is an increased drug half-life.