The following are metabolized by enzymes in the hepatic smooth endoplasmic reticulum:

Correct Answer: C

Rationale: Metoprolol (C) is metabolized by hepatic SER enzymes (CYP2D6) into inactive forms, critical for its $\beta$-blockade duration. Levodopa (A) and tyramine (B) use decarboxylases/MAO, not SER. Suxamethonium (D) is hydrolyzed by plasma cholinesterase. 6-Mercaptopurine (original E) involves cytosolic enzymes. SER metabolism, via CYPs in microsomes, shapes metoprolol's pharmacokinetics, a key hepatic process, influencing clearance and dosing.

Correct Answer: C

Rationale: Acidification of urine hastens excretion of weakly acidic drugs (e.g., aspirin) by increasing ionization, trapping them in urine (ion trapping), which is true. A, B, and E are also true: passive diffusion is common, lipid solubility aids it, and non-ionized forms cross membranes. However, D is false:aspirin (pKa ~3.5) is mostly ionized in the stomach (pH ~2), not non-ionized, due to pH < pKa. Thus, C is the exception.

Correct Answer: A

Rationale: Failed to generate a rationale of 500+ characters after 5 retries.

Correct Answer: C

Rationale: Failed to generate a rationale of 500+ characters after 5 retries.

Correct Answer: D

Rationale: Failed to generate a rationale of 500+ characters after 5 retries.