Pick out the correct definition of a toxic dose:

Correct Answer: B

Rationale: The correct definition of a toxic dose is B: The amount of substance to produce effects hazardous for an organism. This is because a toxic dose refers to the quantity of a substance that can cause harm or adverse effects to an organism. It is important to differentiate between toxic doses and other types of doses, such as therapeutic doses (choice C) which produce the desired effect without causing harm. Choices A and D are incorrect as they do not accurately describe a toxic dose and are not related to the harmful effects of a substance on an organism.

Correct Answer: C

Rationale: Correct Answer: C (Pralidoxime) Rationale: 1. Pralidoxime reactivates inhibited cholinesterase enzymes. 2. This helps counteract the toxic effects of organophosphate cholinesterase inhibitors. 3. Atropine is used to treat the symptoms but does not directly counteract the toxic effects. 4. Pilocarpine and edrophonium are not used for acute toxic effects of organophosphate poisoning.

Correct Answer: C

Rationale: Step-by-step rationale: 1. Succinylcholine causes transient muscle fasciculations due to its depolarizing mechanism of action. 2. It binds to nicotinic acetylcholine receptors, causing initial muscle twitching. 3. This fasciculation phase is a distinct feature of succinylcholine. 4. Mivacurium, Pancuronium, and Tubocurarine are non-depolarizing blockers, so they do not cause initial muscle fasciculations. Summary: A, B, and D are incorrect because they are non-depolarizing blockers and do not induce muscle fasciculations like succinylcholine.

Correct Answer: D

Rationale: Isoproterenol is a nonselective beta receptor agonist. It activates both beta1 and beta2 adrenergic receptors. This is because it has a higher affinity for beta receptors compared to alpha receptors, making it nonselective. Therefore, option D is correct. Option A is incorrect because isoproterenol does not significantly activate alpha receptors. Option B is incorrect as it is not beta1-selective. Option C is incorrect as isoproterenol activates both beta1 and beta2 receptors.

Correct Answer: B

Rationale: The correct answer is B because propranolol does not reduce blood flow to the brain. Propranolol is a non-selective beta-blocker that decreases cardiac work and oxygen demand (choice A), inhibits renin secretion (choice C), and increases the atrioventricular nodal refractory period (choice D). By blocking beta receptors in the heart and blood vessels, propranolol reduces heart rate, contractility, and blood pressure, leading to decreased oxygen demand. Inhibiting renin secretion helps lower blood pressure. Increasing the atrioventricular nodal refractory period can slow down the conduction of electrical impulses in the heart, helping to control heart rhythm. Therefore, choices A, C, and D are all accurate effects of propranolol on the cardiovascular system.