Question 1

Which of the following statements best describes the role of cytochrome P450 enzymes in Phase I drug metabolism?

Accepted Answer

They perform functionalization reactions such as aliphatic and aromatic hydroxylation, dealkylation, and epoxidation, primarily in the endoplasmic reticulum.

Question 2

A drug containing an aromatic ring undergoes Phase I metabolism resulting in the introduction of a hydroxyl group at the para position. Which reaction is most likely responsible?

Accepted Answer

Aromatic hydroxylation

Question 3

Which equation correctly represents the oxidation of ethanol by cytochrome P450?

Accepted Answer

$$ \mathrm{CH_3CH_2OH} + \mathrm{O_2$} \rightarrow \mathrm{CH_3CHO} + \mathrm{H_2O} $$

Question 4

Which Phase I reaction is responsible for the conversion of codeine to morphine?

Accepted Answer

O-demethylation (a type of dealkylation)

Question 5

Which of the following is TRUE regarding flavin-containing mono-oxygenases (FMO)?

Accepted Answer

They are less likely to be induced or inhibited by other drugs compared to cytochrome P450.

Question 6

Which statement best explains why some drugs do not require metabolism for elimination?

Accepted Answer

They are already hydrophilic and can be directly excreted without modification.

Question 7

Which of the following reactions involves the removal of an alkyl group adjacent to a heteroatom, resulting in the formation of an aldehyde?

Accepted Answer

Dealkylation

Question 8

What is the main difference between reversible and apparent reversible reduction reactions in Phase I metabolism?

Accepted Answer

Reversible reactions use the same enzyme for both oxidation and reduction, while apparent reversible reactions use different enzymes for each direction.

Question 9

Which enzyme system is primarily responsible for the oxidation of endogenous purines such as xanthine and theophylline?

Accepted Answer

Xanthine oxidase

Question 10

Which of the following is a correct statement about the hydrolysis of esters and amides?

Accepted Answer

Esters are generally hydrolyzed at a faster rate than amides.

Question 11

Which of the following reactions is most likely to occur in drugs with unsaturated groups, resulting in the formation of a cyclic ether intermediate?

Accepted Answer

Epoxidation

Question 12

During oxidative deamination of amphetamine, what is the fate of the amine group?

Accepted Answer

It is released as ammonium ion ($$ \mathrm{NH_4$^+} ).$$

Question 13

Which of the following is a product of S-oxidation of thioridazine?

Accepted Answer

Sulphoxide and sulphone metabolites

Question 14

Which statement about the nomenclature of cytochrome P450 isoforms is correct?

Accepted Answer

CYP2C9 and CYP2C19 are subfamily members of CYP2.

Question 15

Which of the following is TRUE regarding the reduction of warfarin in Phase I metabolism?

Accepted Answer

It produces a mixture of diastereoisomers due to the formation of a new chiral center.

Question 16

Which of the following statements about xanthine oxidase is correct?

Accepted Answer

It uses water as the source of oxygen incorporated into substrates.

Question 17

Which of the following is a correct description of the role of NADPH in Phase I reduction reactions?

Accepted Answer

NADPH acts as a cofactor and is required for the reduction reactions catalyzed by cytochrome P450.

Question 18

Which of the following is TRUE regarding the hydrolysis of acetylcholine and succinylcholine?

Accepted Answer

Succinylcholine is hydrolyzed at a slower rate than acetylcholine due to its larger size.

Question 19

Which of the following reactions is catalyzed by both microsomal and non-microsomal enzymes?

Accepted Answer

Reduction of epoxides

Biotransformation: Phase I Reactions in Drug Metabolism

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