Distribution of drugs to specific tissues

Correct Answer: C

Rationale: The correct answer is that distribution depends on the unbound drug concentration gradient between blood and tissue (C). Only free (unbound) drug can cross membranes into tissues, driven by the concentration gradient, as per Fick's law of diffusion. Option A is false; blood flow (e.g., high to brain, low to fat) significantly affects distribution, as seen with anesthetics. Option B is incorrect; tissue solubility (lipid vs. aqueous) determines partitioning, like thiopental in fat. Option D is wrong; strong plasma protein binding (e.g., warfarin) reduces free drug, limiting distribution. Option E (original) about half-life is unrelated. This gradient-driven process explains rapid onset in highly perfused organs and prolonged effects in poorly perfused ones, critical for therapeutic targeting and avoiding toxicity.

Correct Answer: D

Rationale: The Ames test detects mutagenesis in bacteria (D), using Salmonella strains to identify reverse mutations from chemicals (e.g., aflatoxin), a rapid screen for potential carcinogens due to mutation-cancer correlation. Options A and B (carcinogenesis) require animal models, not bacteria. Option C (teratogenesis) involves developmental toxicity, not the Ames focus. Option E (original) is redundant with D. Developed by Bruce Ames, this assay's simplicity and sensitivity make it a cornerstone in genotoxicity screening, though positive results need animal confirmation for carcinogenicity, balancing cost and predictive power.

Correct Answer: A

Rationale: Blood flow to the tissue is an important determinant (A), as highly perfused organs (e.g., brain, heart) receive drugs faster, influencing onset (e.g., anesthetics). Solubility (B) affects partitioning (e.g., lipophilic drugs into fat), but blood flow drives initial delivery. Concentration (C) sets the gradient, but flow dictates access. Tissue size (D) impacts total drug amount, not rate. Option E (original) is true but A is primary. This perfusion-limited distribution explains rapid effects in critical organs and slower accumulation in fat, guiding drug design and dosing schedules.

Correct Answer: D

Rationale: Aspirin (pKa 3.49) is most soluble at pH 4.0 (D). As a weak acid, its solubility increases when ionized (A⁻ form), per Henderson-Hasselbalch: pH = pKa + log([A⁻]/[HA]). At pH 4.0, pH > pKa, favoring ionization (log(0.51) ≈ 0.2, [A⁻] > [HA]), enhancing water solubility. At pH 1.0 (A), 2.0 (B), and 3.0 (C), pH < pKa, aspirin is mostly un-ionized (lipid-soluble), less soluble. pH 6.0 (original E) increases solubility further, but D is closest optimal. This pH-dependent solubility aids aspirin's absorption in the intestine (pH ~6), not stomach (pH ~2), guiding formulation strategies.

Correct Answer: B

Rationale: A very fine powder completely passes through a #120 sieve (B), with mesh size ~125 μm, per USP standards, ensuring small, uniform particles for rapid dissolution (e.g., in suspensions). Option A (#80, ~180 μm) is fine, not very fine. Option C (#20, ~850 μm) is coarse. Option D describes a fine powder range. Option E (original) is coarser still. This fineness enhances bioavailability and mixing, critical in formulations where particle size affects absorption rates, like oral powders or inhalants.