Which of the following statements about spare receptors is most correct?

Correct Answer: B

Rationale: The most correct statement is that spare receptors will be detected if the intracellular effect of drug-receptor interaction lasts longer than the drug-receptor interaction itself (B). Spare receptors exist when maximal response occurs before all receptors are occupied (e.g., histamine on H2 receptors), detectable when downstream signaling (e.g., cAMP) persists post-dissociation. Option A is false; spare receptors are membrane-bound, not cytoplasmic. Option C is incorrect; maximal efficacy is set by receptor-effector coupling, not spare receptor number. Option D is wrong; receptors need agonists for activation. Option E (original) is incorrect; EC50 < Kd indicates spare receptors, not the reverse. This phenomenon increases sensitivity, explaining why low agonist doses can achieve full effects in systems like beta-adrenergic signaling.

Correct Answer: A

Rationale: Phenylephrine causes constriction of vessels in the nasal mucosa (A), an alpha-1 agonist shrinking mucosal blood vessels, reducing congestion (e.g., in decongestants). It doesn't increase gastric secretion/motility (B), a cholinergic effect. It decreases skin temperature (C is incorrect) by vasoconstriction. It causes mydriasis (D is incorrect), not miosis, via pupil dilation. Option E (original) is false. This selective alpha-adrenergic action underlies its topical/systemic use, with minimal beta effects, though reflex bradycardia or hypertension may occur, requiring cautious use in cardiovascular patients.

Correct Answer: B

Rationale: The Henderson-Hasselbalch equation (B) calculates the pH of a buffer system, pH = pKa + log([A⁻]/[HA]), balancing weak acid/base and conjugate forms (e.g., acetate buffer). Noyes-Whitney (A) governs dissolution rates. Michaelis-Menten (C) describes enzyme kinetics. Yong (D) and Stokes (original E) are unrelated to buffers. This equation predicts ionization (e.g., aspirin at pH 7.4), crucial for drug absorption and formulation stability, maintaining pH despite acid/base challenges, a key principle in pharmaceutical buffering.

Correct Answer: D

Rationale: Vanishing cream is an emulsion base (D), typically oil-in-water (o/w), disappearing on skin application as water evaporates, leaving a non-greasy film (e.g., cosmetic creams). Water-soluble bases (A) dissolve in water (e.g., PEG ointments), oleaginous bases (B) are greasy (e.g., petrolatum), and absorption bases (C) absorb water (e.g., lanolin). Option E (original) is invalid. This o/w emulsion enhances drug delivery (e.g., hydrocortisone) and patient compliance due to its aesthetic appeal, contrasting with greasy bases in topical formulations.

Correct Answer: A

Rationale: Sorbitol (A) makes soft gelatin capsule shells elastic or plastic-like, a polyol plasticizer softening the gelatin matrix, enhancing flexibility (e.g., vitamin D capsules). Povidone (B) is a binder, not a plasticizer here. Polyethylene glycol (C) can plasticize but is less common. Lactose (D) is a filler, not elasticizing. pKa (original E) is irrelevant. Sorbitol's hygroscopicity maintains shell integrity, improving handling and patient acceptability in liquid-filled capsules, a key formulation advantage.