Besides serum creatinine and eGFR, which measurement may influence dosing of renally cleared medications?

• A. Urine output
• B. Blood pressure
• C. Heart rate
• D. Temperature

Answer: (A)

Renal drug clearance depends on how the kidneys are actually excreting substances at the moment, not just on their filtration capability. Serum creatinine and eGFR give a snapshot of filtration function, but urine output provides direct, real-time information about how much drug is being eliminated. If urine production drops (oliguria), clearance falls, drug levels can accumulate, and dosing often needs to be reduced or dosing intervals lengthened. When urine output is adequate, dosing can be guided more confidently by filtration estimates. Other measurements like blood pressure, heart rate, or temperature don’t directly reflect the kidney’s current excretion of a drug and are less informative for adjusting doses of renally cleared medications.