All of the following are general mechanisms of drug permeation Except

Correct Answer: B

Rationale: Aqueous hydrolysis is the correct answer because it is not a mechanism of drug permeation across biological membranes. Permeation refers to the process by which drugs move across cell membranes to reach their site of action, and it includes aqueous diffusion (A), where drugs pass through aqueous channels or pores; lipid diffusion (C), where lipophilic drugs dissolve into the lipid bilayer; and pinocytosis or endocytosis (D), where cells engulf drugs in vesicles. Special carrier transport (original E) involves specific proteins facilitating drug movement. Aqueous hydrolysis (B), however, is a chemical degradation process where a drug reacts with water, breaking chemical bonds (e.g., in esters or amides), not a physical movement across membranes. This distinction is critical in pharmacology, as permeation mechanisms determine bioavailability and tissue distribution, while hydrolysis affects drug stability, often in the gastrointestinal tract or plasma, not membrane crossing.

Correct Answer: A

Rationale: Phase I involves the study of a small number of normal volunteers by highly trained clinical pharmacologists (A), assessing safety, pharmacokinetics, and tolerability (e.g., 20-100 subjects) in controlled settings. Phase II (B) tests efficacy in patients (100-300), not thousands. Phase III (C) compares efficacy and safety in larger populations (300-3000), not inducing toxicity for therapeutic index. Option D is irrelevant. Phase II with controls (original E) is true but less defining than A. Phase I's focus on healthy subjects establishes safe dosing, critical for advancing drug development, balancing risk and scientific rigor.

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.