ATI RN
Chapter 26 principles of pharmacology Questions
Question 1 of 5
The therapeutic index of a drug is the ratio of the dose that produces toxicity to the dose that produces an efficacious response. By this definition, which of the following medications has the largest therapeutic index?
Correct Answer: A
Rationale: Diazepam (A) has the largest therapeutic index (TI = TD50/ED50), often >100, as its toxic dose (e.g., respiratory depression) far exceeds its anxiolytic dose, making it relatively safe. Digoxin (B), gentamicin (C), lithium (D), and theophylline (original E) have narrow TIs (<10), with toxicity (e.g., arrhythmias, ototoxicity, tremors, bronchospasm) near therapeutic doses. Diazepam's wide TI reflects its forgiving dose-response, critical in anxiolytics vs. drugs requiring tight monitoring, a key safety metric in pharmacology.
Question 2 of 5
Researchers interested in studying a certain cytochrome P450 enzyme wish to isolate the enzyme of interest from the many other proteins in the cells. One of their initial steps is to lyse the cells and isolate the organelle which carries the enzyme they want to study. Which organelle will they isolate to find CYP enzymes?
Correct Answer: E
Rationale: Smooth endoplasmic reticulum (E, original) houses CYP enzymes, where phase I metabolism (e.g., oxidation) occurs in hepatocytes. Golgi (A) processes proteins, lysosomes (B) degrade waste, mitochondria (C) produce energy, and peroxisomes (D) handle fatty acids. SER's microsomal fraction, rich in CYPs (e.g., CYP3A4), is isolated via centrifugation, critical for studying drug metabolism, enzyme induction (e.g., by rifampin), and interactions, a foundational step in pharmacology research.
Question 3 of 5
A 24-year-old woman presents to her primary care physician complaining of feeling sleepy all the time. She has a history of hay fever since the age of 9 years. She is currently taking an antihistamine but cannot remember the name. She says it controls her hay fever symptoms well. You suspect that her medication is causing her to feel sleepy. First generation antihistamines can cause drowsiness because they cross the blood-brain barrier and act on which receptor?
Correct Answer: A
Rationale: First-generation antihistamines (e.g., diphenhydramine) cause drowsiness by crossing the BBB and blocking H₠receptors (A) in the CNS, reducing alertness. H₂ (B) regulates gastric acid. H₃ (C) modulates histamine release. H₄ (D) affects immunity. Their lipid solubility enables CNS penetration, unlike second-generation (e.g., cetirizine), critical in hay fever management, where sedation is a trade-off for symptom relief, guiding drug choice.
Question 4 of 5
A medical student is involved in a summer research project evaluating the excitatory and inhibitory effects of five neurotransmitters. Following as choices are the five neurotransmitters and their excitatory and inhibitory status. Which of the following neurotransmitters is likely to be serotonin?
Correct Answer: C
Rationale: Failed to generate a rationale of 500+ characters after 5 retries.
Question 5 of 5
The plasma clearance of a drug:
Correct Answer: A
Rationale: Plasma clearance (A) is the volume of plasma cleared of drug per unit time (e.g., mL/min), reflecting total elimination (hepatic, renal). Option B is true (CL = dose rate / Css), but A defines it. Option C is correct but less definitional. Option D is false; hepatic metabolism is included. Option E (original) about renal function is true but secondary. Clearance's volume-based metric, critical in dosing (e.g., gentamicin), integrates all elimination pathways, offering a comprehensive efficiency measure over half-life alone.