Which of the following best describes the mechanism of action of beta-blockers in managing heart failure?

Correct Answer: C

Rationale: Step 1: Beta-blockers block the effects of adrenaline on beta receptors in the heart. Step 2: Adrenaline (epinephrine) binds to beta receptors in the heart, leading to increased heart rate and contractility. Step 3: By blocking beta receptors, beta-blockers reduce heart rate and contractility. Step 4: This reduces the workload on the heart, improves efficiency, and helps in managing heart failure. Summary: A: Incorrect. Beta-blockers actually decrease heart rate and contractility. B: Incorrect. Beta-blockers primarily affect heart function, not preload and afterload. D: Incorrect. Beta-blockers do not directly increase cardiac output; they improve heart function by reducing workload.

Correct Answer: C

Rationale: Rationale for Choice C: In noncompetitive antagonism, the antagonist binds irreversibly to a site different from the agonist binding site, preventing agonist binding. Increasing agonist concentration cannot overcome this as the antagonist blocks the receptor irreversibly. This results in a fixed maximum response. Summary: A: Incorrect. The potency of the drug may change due to noncompetitive antagonism. B: Incorrect. Noncompetitive antagonism does not affect the number of receptors available to bind the agonist. D: Incorrect. Choice C is correct, making this statement wrong.

Correct Answer: D

Rationale: The correct answer is D: Induction of powerful uterine contracture. Ergonovine is a uterotonic agent that works by stimulating uterine contractions, which helps control postpartum hemorrhage due to uterine atony. The drug acts directly on the smooth muscle of the uterus, leading to increased tone and decreased bleeding. A: Selective constriction of uterine arteries is incorrect because ergonovine primarily acts on the uterine muscle itself, not the blood vessels supplying the uterus. B: Endothelin release in the uterine vascular bed is incorrect as ergonovine does not directly affect endothelin release. C: Platelet aggregation in the uterine vascular bed is incorrect as ergonovine's action is not related to platelet aggregation but rather to uterine muscle contraction. In summary, the therapeutic effect of ergonovine in this patient is mediated by its ability to induce powerful uterine contr

Correct Answer: C

Rationale: The correct answer is C: Ergotamine. Ergotamine is known to cause vasoconstriction, leading to decreased blood flow to extremities, resulting in numbness and tingling. Ibuprofen is a nonsteroidal anti-inflammatory drug and does not typically cause numbness and tingling. Valproic acid is used for epilepsy and mood disorders. Propranolol is a beta-blocker used for hypertension and migraines but is not associated with numbness and tingling in extremities.

Correct Answer: B

Rationale: The correct answer is B: Diphenhydramine. Diphenhydramine is a first-generation antihistamine that can cause anticholinergic toxicity in overdose. The symptoms described in the question such as high body temperature, dry skin, dilated pupils, and agitation are consistent with anticholinergic poisoning. Diphenhydramine also has sedative effects which can lead to seizures in high doses. A: Ibuprofen is a nonsteroidal anti-inflammatory drug and overdose typically presents with symptoms like gastrointestinal upset and kidney injury, not the symptoms described in the question. C: Phenylephrine is a decongestant that can cause hypertension and tachycardia in overdose, not the symptoms described in the question. D: Celecoxib is a selective COX-2 inhibitor used as an NSAID and overdose usually presents with gastrointestinal symptoms, not the symptoms described in the question.