Renal clearance (Clᵣ) is the volume of plasma cleared of a drug by the kidneys per unit time (mL/min or L/h).
It evaluates kidney efficiency in drug elimination and helps determine appropriate drug dosing, especially in renal impairment
Renal Clearance Formula
Where:
ClR = Renal clearance (mL/min)
U = Drug concentration in urine (mg/mL)
V = Urine flow rate (mL/min)
P = Drug concentration in plasma (mg/mL)
Alternatively, renal clearance is estimated using inulin or creatinine, which are freely filtered but not secreted, reabsorbed, or metabolized. Comparing drug clearance with these markers helps assess renal excretion's contribution to drug elimination.
Interpretation of Renal Clearance Values
ClR < 125 mL/min → Drug undergoes reabsorption (e.g., glucose).
ClR ≈ 125 mL/min → Drug is filtered but not reabsorbed or secreted.
ClR > 125 mL/min → Drug undergoes active secretion (e.g., penicillin).
Factors Affecting Renal Clearance
GFR – Higher GFR increases clearance; lower GFR (renal impairment) reduces clearance.
Tubular Secretion – Active transport enhances clearance; competition can cause drug interactions.
Tubular Reabsorption – Lipophilic, non-ionized drugs are reabsorbed; urine pH affects ionization and clearance.
Plasma Protein Binding – Highly protein-bound drugs have lower clearance
