Propofol has a reported systemic clearance approaching 2 litres per minute, a value that exceeds hepatic blood flow in a healthy adult. This observation implies:

• A Measurement error from first-pass pulmonary uptake
• B Zero-order saturation kinetics at clinical doses
• C Predominant renal excretion of unchanged drug
• D Significant extrahepatic metabolism, with the lungs being the major site ✓

Explanation

Clearance cannot exceed organ blood flow if elimination occurs solely in that organ. Since propofol clearance exceeds hepatic blood flow, extrahepatic removal must contribute substantially, and studies using isolated lung preparations confirm the lung as the principal additional site of metabolism, with possible renal contribution. Less than 1 percent appears unchanged in urine, so renal excretion of parent compound is negligible.

Reference: Miller's Anesthesia, 9th ed.

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