Which of the following statements about metabolism is TRUE:

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Question restatement: Which of the following statements about metabolism is TRUE?

Option a: 'CYP3A4 is the most abundant Phase II metabolic enzyme and is responsible for metabolising the majority of drugs on the market.' This is inaccurate because CYP3A4 is a Phase I (not Phase II) enzyme that mainly carries out oxidation reactions; while it metabolizes many drugs, it is not categorized as a Phase II enzyme, and it is not correct to claim it is the most abundant Phase II enzyme or that it metabolizes the majority of drugs on the market.

Option b: 'Drug metabolising enzymes are responsible for the clearance of many drug molecules from the plasma.' This statement is correct. Drug-metabolizing enzymes (primarily Phase I and Phase II enzymes in the liver and other tissues) transform lipophilic drugs into more hydrophilic forms, facilitating elimination from the bloodstream and body. This describes the fundamental purpose of drug metabolism and clearance.

Option c: 'Most drug metabolising enzymes are found in microsomes in the kidneys.' This is misleading. While some drug-metabolizing activity occurs in the kidneys, the liver (specifically hepatic microsomes containing cytochrome P450 enzymes) is the primary site of drug metabolism. Renal microsomes do exist, but they contribute a much smaller portion of overall drug metabolism compared with hepatic enzymes.

Option d: 'Drug metabolism enzymes usually convert hydrophilic drugs to more hydrophobic metabolites.' This is false. The main goal of metabolism is to increase hydrophilicity (water solubility) to enhance excretion; many metabolic reactions (especially Phase I oxidation/reduction and Phase II conjugation) convert lipophilic (hydrophobic) compounds into more polar, hydrophilic metabolites for easier elimination. Therefore, this statement reverses the actual direction of polarity change.

In summary, option b accurately states a core function of drug metabolizing enzymes—contributing to the clearance of many drug molecules from the plasma—whereas the other options contain factual inaccuracies about enzyme location, phase classification, or the hydrophilicity/properties of metabolites.

PHR1022 S2 2025 PA Practice Test for progress test 1

Which of the following statements about metabolism is TRUE:

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