Which of these is NOT a method used by the body to eliminates drugs?以下哪一项不是人体用来排除药物的方法？

Question

BlackTom AI · Accepted Answer

Renal clearance is a pharmacokinetic parameter used to quantify how effectively the kidneys remove a drug from plasma, not a physiological mechanism that itself eliminates drugs.

1) Relevant knowledge points and concepts
- Elimination mechanisms: glomerular filtration (passive filtration of unbound drug into urine), tubular secretion (active transport of drug into tubular fluid), biotransformation (metabolic conversion in liver or tissues making drugs more water‑soluble), and routes like biliary excretion and pulmonary exhalation.  
- Renal handling equation and clearance concept: renal clearance (CLR) is a calculated value reflecting net kidney removal: CLR = (U × V) / P where U = urine drug concentration, V = urine flow rate, P = plasma drug concentration. It can also be described as CLR = filtration + secretion − reabsorption.

2) Step-by-step reasoning
- Glomerular filtration: unbound drug is physically filtered at the glomerulus into the tubular lumen → this directly contributes to elimination. (So option a is a true elimination mechanism.)
- Biotransformation: hepatic and extrahepatic enzymes chemically alter drugs, often producing polar metabolites that are more readily excreted → this is a main elimination pathway. (Option b is correct as an elimination method.)
- Tubular reabsorption: movement of drug from tubular fluid back into blood; this reduces urinary excretion and therefore is a renal handling process that affects elimination (it opposes elimination), but it is a physiological process in renal drug handling. (Option d is a physiological mechanism involved in renal handling.)
- Renal clearance: computed measure (units mL/min) summarizing net effect of filtration, secretion and reabsorption; it is not itself a mechanism that eliminates drug but a way to quantify elimination. Example calculation: if urine concentration U = 50 mg/L, urine flow V = 1 mL/min, plasma concentration P = 0.5 mg/L, then CLR = (50 mg/L × 1 mL/min) / 0.5 mg/L = 100 mL/min.

3) Why the correct answer is correct
Because renal clearance is a pharmacokinetic metric (a calculated rate), not a physiological process that actively removes drug. The other options describe physiological processes (filtration and biotransformation actively promote elimination; tubular reabsorption is a renal process that modifies elimination).

4) Why other options are incorrect
- a: Glomerular filtration is a direct elimination route.  
- b: Biotransformation (metabolism) converts drugs to excretable forms.  
- d: Tubular reabsorption is a renal process affecting excretion (it returns drug to blood and thus influences elimination), so it is part of renal handling.

Conclusion: Renal clearance (option c) is not a method used by the body to eliminate drugs, therefore the correct answer is c, matching the provided answer.

Which of these is NOT a method used by the body to eliminates drugs?以下哪一项不是人体用来排除药物的方法？单项选择题

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