ATI RN
Ch 30 principles of pharmacology Questions
Question 1 of 5
The P-glycoprotein is a multidrug transmembrane transporter protein that transports medications across cell membranes. Functions of this protein include
Correct Answer: B
Rationale: P-glycoprotein (P-gp) transports drugs into liver hepatocytes (B), effluxing substrates (e.g., digoxin) into bile for elimination, a key hepatic function. It pumps drugs out of cells (e.g., into intestinal lumen or bile), not into urine (A, renal role). It limits fetal entry (C is opposite), protecting the fetus. It effluxes drugs from enterocytes to lumen (D is reversed). Brain efflux (original E) restricts CNS entry. P-gp's hepatic role reduces bioavailability, critical in drug interactions (e.g., with rifampin), influencing pharmacokinetics in liver-centric metabolism.
Question 2 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 3 of 5
A 17-year-old pregnant female asks her doctor what she can do about her acne. The doctor prescribes a topical benzoyl peroxide preparation, but the patient is unsatisfied with the results. She has a close friend taking a vitamin A-based acne control product, and her friend often tells her how well it works. She begins taking her friend's pills and is pleased with the reduction in her acne. During which prenatal period is her unborn child at greatest risk for developing a birth defect?
Correct Answer: C
Rationale: Days 18-55 (C) pose the greatest risk for birth defects from isotretinoin (vitamin A-based, e.g., Accutane), a teratogen causing craniofacial, cardiac, and CNS defects during organogenesis. Pre-conception (A) affects germ cells, not direct defects. Days 1-17 (B) risk implantation failure, not malformation. Days 56-birth (D) affect growth, not structure. Option E (original) is false; vitamin A is teratogenic. This critical period, weeks 3-8, underscores isotretinoin's Category X status, necessitating strict contraception, a major concern in pregnancy pharmacology.
Question 4 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 5 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.