ATI RN
Ch 30 principles of pharmacology Questions
Question 1 of 5
A 27-year-old woman takes phenytoin to control focal seizures. Most of the phenytoin in her blood is plasma-protein bound, and only the free fraction is pharmacologically active. The free fraction must diffuse through many barriers to reach its site of action. Many characteristics influence a drug's ability to diffuse across biologic membranes. Which of the following possible drug characteristics would aid such diffusion?
Correct Answer: D
Rationale: A weak base with pKa of 7 (D) aids diffusion across membranes (e.g., to CNS for phenytoin's antiseizure effect). At physiologic pH (7.4), it's mostly un-ionized (lipid-soluble), per Henderson-Hasselbalch, enhancing permeability. Hydrophilicity (A) hinders lipid bilayer crossing. Large size (B) slows diffusion. A weak acid pKa 7 (C) is ionized at pH 7.4, less permeable. Phenytoin (weak acid, pKa ~8) behaves similarly, but D fits typical CNS drugs. Lipid solubility drives BBB crossing, critical for anticonvulsant efficacy.
Question 2 of 5
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 (tâ‚/â‚‚ 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.
Question 3 of 5
The following drugs are reversible competitive antagonists:
Correct Answer: C
Rationale: Ranitidine (C) is a reversible competitive antagonist at Hâ‚‚ receptors, reducing gastric acid secretion, displaced by excess histamine. Suxamethonium (A) is a depolarizing neuromuscular blocker, not competitive. Loratadine (B) is an Hâ‚ antagonist, also correct but C is selected. Phenoxybenzamine (D) is an irreversible $\alpha$-blocker. Naloxone (original E) is a reversible opioid antagonist, another fit. Competitive antagonism, as with ranitidine, allows surmountability by agonists, critical in managing acid-related disorders, distinguishing it from irreversible binding in pharmacotherapy.
Question 4 of 5
The following drugs have an elimination half-life of less than 4 hours in a healthy adult:
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.
Question 5 of 5
Drug absorption following oral administration:
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.