What is the impact of renal impairment on the pharmacokinetics of drugs that are renally cleared?

• A. Renal impairment increases clearance.
• B. Renal impairment reduces clearance, increases AUC and t1/2; may require dose reduction or interval extension.
• C. Renal impairment has no effect on PK.
• D. Renal impairment only affects Vd.

Answer: (B)

When a drug is cleared mainly by the kidneys, its elimination depends on renal function. In renal impairment, glomerular filtration and possibly tubular secretion decrease, so clearance falls. With lower clearance, the body cannot remove the drug as quickly, leading to higher systemic exposure (increased AUC) and a longer elimination half-life. If dosing continues at the same rate, the drug accumulates, raising the risk of toxicity. To manage this, you typically reduce the dose or extend the dosing interval to keep exposure within the therapeutic range. The idea is that AUC is inversely related to clearance, and t1/2 increases as clearance decreases.