Which of the following provides information about the variation in sensitivity of the drug within the population studied?

Correct Answer: D

Rationale: Quantal dose-response curves (D) provide information about variation in drug sensitivity within a population, plotting the percentage of subjects responding (e.g., pain relief) against dose, revealing ED50 and variability (e.g., standard deviation). Maximal efficacy (A) measures the maximum effect (graded curves). Therapeutic index (B) is TD50/ED50, assessing safety, not sensitivity spread. Drug potency (C) compares doses for equal effects (e.g., ED50), not population variation. Graded curves (original E) measure continuous responses, not all-or-none. Quantal curves, used in clinical and preclinical studies, highlight interindividual differences (e.g., genetic polymorphisms), guiding dosing adjustments for diverse populations.

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.

Correct Answer: A

Rationale: Divided powders are dispensed in individual-dose packets (A), pre-measured paper or foil packets (e.g., headache powders) ensuring accurate dosing and convenience. Bulk containers (B) suit undivided powders. Sifter-type containers (C) are for topical use, not oral doses. No option D or original E exists. This packaging protects hygroscopic or unstable drugs, enhancing patient compliance and stability, a traditional yet effective dispensing method in pharmacy practice.