In renal impairment, what happens to drug clearance and half-life, and what is the typical dosing implication?

• A. Clearance decreases, half-life decreases; increase dosing interval.
• B. Clearance increases, half-life increases; reduce dose.
• C. Clearance decreases, half-life increases; reduce dosing interval or dose.
• D. Clearance remains the same; no dose adjustment needed.

Answer: (C)

When kidney function is reduced, the body's ability to clear the drug decreases, so elimination slows down. Because the elimination half-life is determined by t1/2 = 0.693 × Vd / Cl, a drop in clearance lengthens the half-life (assuming the volume of distribution remains constant or doesn’t compensate fully). With a longer half-life, the drug lingers longer in the body, increasing the risk of accumulation if dosing isn’t adjusted. To prevent toxicity, you adjust by either lowering the dose or extending the dosing interval (or both), with the exact approach depending on how severely the kidneys are impaired and how the drug is cleared.