- What is the primary goal of xenobiotic biotransformation?
A. To make chemicals more fat-soluble
B. To enhance absorption in the GI tract
C. To increase water solubility for easier excretion
D. To convert drugs into proteins
Answer: C
Explanation: Biotransformation makes xenobiotics more water-soluble so they can be excreted more easily.
- Which of the following is a Phase I reaction?
A. Glucuronidation
B. Oxidation
C. Sulfonation
D. Glutathione conjugation
Answer: B
Explanation: Oxidation is a Phase I reaction; the others are Phase II conjugation reactions.
- Which enzymes are most involved in Phase I oxidative metabolism of drugs?
A. UGTs
B. GSTs
C. Cytochrome P450s (CYPs)
D. COMT
Answer: C
Explanation: CYP enzymes are the major enzymes responsible for Phase I oxidation of drugs.
- What do Phase II reactions typically do to a chemical?
A. Make it more lipid-soluble
B. Conjugate it to increase water solubility
C. Oxidize the molecule
D. Inhibit its elimination
Answer: B
Explanation: Phase II reactions attach polar groups to xenobiotics, increasing water solubility and promoting excretion.
- Which CYP enzyme is responsible for metabolizing over 50% of drugs?
A. CYP2D6
B. CYP2C9
C. CYP3A4
D. CYP1A2
Answer: C
Explanation: CYP3A4 is the most abundant and versatile CYP enzyme in drug metabolism.
- Which of the following enzymes converts codeine to morphine?
A. CYP2C19
B. CYP2D6
C. FMO3
D. MAO-B
Answer: B
Explanation: CYP2D6 activates codeine by converting it into the active analgesic morphine.
- Which statement about CYP polymorphisms is TRUE?
A. They do not affect drug response.
B. They can lead to poor or ultra-rapid drug metabolism.
C. They only occur in rodents.
D. They only affect Phase II metabolism.
Answer: B
Explanation: Genetic polymorphisms in CYP enzymes lead to variations in metabolism and drug response.
- Which enzyme family is involved in conjugation of chemicals with glutathione?
A. SULTs
B. GSTs
C. ADHs
D. CYPs
Answer: B
Explanation: GSTs (Glutathione S-transferases) catalyze the conjugation of glutathione to reactive compounds.
- Which enzyme group is heat-sensitive and helps distinguish between CYP and non-CYP metabolism?
A. UGTs
B. MAOs
C. FMOs
D. NATs
Answer: C
Explanation: FMOs are heat-labile and can be inactivated at 50°C, unlike CYPs.
- Which of the following can inhibit CYP3A4 and cause drug-drug interactions?
A. Ranitidine
B. Ketoconazole
C. Omeprazole
D. Tamoxifen
Answer: B
Explanation: Ketoconazole is a known potent inhibitor of CYP3A4, leading to elevated levels of drugs metabolized by this enzyme.
