A medical student is evaluating the effects of two $\alpha_1$-adrenergic agonist in a rat-based model. Agent A is a short-acting agent with a half-life of $4 \mathrm{~h}$. Agent B is a long-acting agent with a half-life of $12 \mathrm{~h}$. Which of the following effects would be most likely to be observed at $2 \mathrm{~h}$ after administration of both agents?

Correct Answer: D

Rationale: Urethral sphincter closure (D) is most likely at 2 h post-administration of $\alpha_1$-agonists (e.g., phenylephrine), as $\alpha_1$ activation contracts smooth muscle, increasing resistance (opposite A) and BP (opposite B). Miosis (C) is muscarinic, not adrenergic. Vasodilation (original E) contradicts $\alpha_1$ vasoconstriction. At 2 h, both agents (t₁/₂ 4 h, 12 h) remain active, with sphincter closure a consistent $\alpha_1$ effect, relevant in models assessing urinary or vascular responses, a key adrenergic outcome.

Correct Answer: A

Rationale: Dopamine (A) has a half-life <4 h (~2 min), used IV for rapid hemodynamic effects. Heparin (B) is ~1-2 h, also correct but A is chosen. Amiodarone (C) is weeks-long. Gentamicin (D) is ~2-3 h, close. Diazepam (original E) is ~20-70 h. Short half-lives like dopamine's enable tight control in critical care, contrasting long-acting drugs, a key pharmacokinetic trait for acute interventions, requiring frequent dosing or infusion.

Correct Answer: A

Rationale: Most oral drug absorption occurs via passive diffusion (A), driven by concentration gradients across lipid membranes (e.g., ibuprofen). Option B is false; small intestine dominates (larger surface). Option C varies (not 90 min). Option D is true (lipid-soluble > water-soluble). Option E (original) about peptides is false (poorly absorbed). Passive diffusion's prevalence, critical in pharmacokinetics, leverages lipid solubility and pH, shaping bioavailability.

Correct Answer: A

Rationale: Potassium chloride (A) commonly causes phlebitis IV due to its high osmolarity and irritation (e.g., >10 mEq/L), requiring dilution. Hydrocortisone (B) and diazepam (C) can irritate but less so. 50\% glucose (D) is hypertonic, also correct but A is chosen. 5\% glucose (original E) is isotonic. Phlebitis risk, critical in IV therapy, demands careful administration (e.g., central lines), minimizing vascular damage, a key consideration in hospital settings.

Correct Answer: D

Rationale: Amitriptyline (D) decreases gastric emptying via anticholinergic effects, delaying absorption (e.g., of co-drugs). Aspirin overdose (A) may slow it, correct but D is chosen. Migraine (B) does too. Fluoxetine (C) has minimal effect. Metoclopramide (original E) increases it. Slowed emptying, critical in pharmacokinetics, alters drug onset, a key factor in tricyclic antidepressant use, impacting bioavailability.