Understand drug excretion.

For a drug to be excreted unchanged in the urine, it must be sufficiently water-soluble (hydrophilic) to remain in the aqueous environment of the urine and not be reabsorbed back into the bloodstream by the renal tubules.

• A. One which is non-polar: Non-polar drugs are lipid-soluble and tend to be reabsorbed from the renal tubules, requiring metabolism to more polar forms for excretion.
• B. One which is hydrophilic: Hydrophilic drugs are water-soluble and are poorly reabsorbed, making them likely to be excreted unchanged.
• C. One with low ionization at glomerular filtrate: Low ionization means the drug is mostly in its uncharged form, which is more lipid-soluble and thus more easily reabsorbed.
• D. An acidic drug in acidified urine: An acidic drug in acidified urine will be largely in its un-ionized form, which is lipid-soluble and reabsorbed. For an acidic drug to be excreted, the urine should be alkaline to keep it in its ionized form.

A hydrophilic drug is most likely to be excreted unchanged in the urine.

The correct option is B.
$\boxed{\text{B. One which is hydrophilic}}$

Question 2: Which of the following statements best explains why the class of antibiotics to which the drugs above belongs does not destroy human cells but only microbial cells? (Referring to Figure 1, which shows an aminoglycoside antibiotic).

Figure 1 shows a structure characteristic of an aminoglycoside antibiotic (e.g., streptomycin, gentamicin). These antibiotics are known to inhibit bacterial protein synthesis.

Aminoglycosides exert their antibacterial effect by binding to the 30S ribosomal subunit of bacteria, thereby inhibiting protein synthesis. The selective toxicity of these drugs (meaning they harm bacteria but not human cells) arises from structural differences between bacterial and human ribosomes.

• A. Human cells have cholesterol instead of ergosterol: This relates to antifungal drugs targeting fungal cell membranes, not aminoglycosides.
• B. Human cells obtain folic acid from the diet: This relates to sulfonamides and trimethoprim, which inhibit bacterial folic acid synthesis.
• C. Human cells have a lower affinity for the drug: While true, it's a consequence of the structural difference, not the fundamental reason.
• D. Human cells have a different size of ribosome: Bacterial ribosomes are 70S (composed of 30S and 50S subunits), while human (eukaryotic) ribosomes are 80S (composed of 40S and 60S subunits). Aminoglycosides specifically target the bacterial 30S subunit, which is structurally distinct from the eukaryotic 40S subunit, leading to selective toxicity.

The difference in ribosomal size and structure is the primary reason for the selective toxicity of aminoglycosides.

The correct option is D.
$\boxed{\text{D. Human cells have a different size of ribosome}}$

Figure 2 shows a 1,4-benzodiazepine derivative with a methyl group at N1 and a chlorine atom at C7. This structure is typical of many benzodiazepine drugs.

Benzodiazepines typically undergo Phase I (functionalization) reactions such as N-dealkylation (