Though ethacrynic acid is also a high-ceiling diuretic, it is rarely used compared to furosemide because

Correct Answer: D

Rationale: In the context of CNS drugs pharmacology, understanding the differences between ethacrynic acid and furosemide is crucial for safe and effective prescribing practices. The correct answer, D) All of the above, is the most appropriate choice because it encapsulates the main reasons why ethacrynic acid is rarely used compared to furosemide. Firstly, ethacrynic acid is more ototoxic compared to furosemide. Ototoxicity refers to the potential of a drug to cause damage to the ear, particularly the auditory system. This side effect can lead to hearing loss, dizziness, and balance disturbances, making ethacrynic acid a less favorable option in clinical practice. Secondly, ethacrynic acid is known to cause diarrhea and gut bleeding. These gastrointestinal side effects can significantly impact a patient's quality of life and may lead to complications such as dehydration, electrolyte imbalances, and gastrointestinal bleeding. Additionally, ethacrynic acid exhibits a steep increase in diuretic response over a narrow dose range. This means that small changes in dosage can result in significant changes in diuretic effect, increasing the risk of dose-related adverse reactions and therapeutic challenges. Conversely, furosemide is preferred over ethacrynic acid in clinical practice due to its relatively lower ototoxicity, milder gastrointestinal side effects, and a broader therapeutic window, allowing for more predictable and manageable dosing. Educationally, this question highlights the importance of understanding the nuances of high-ceiling diuretics in pharmacology. By grasping the specific differences between ethacrynic acid and furosemide, healthcare professionals can make informed decisions when selecting the most appropriate treatment options for patients with conditions requiring diuretic therapy.

Correct Answer: A

Rationale: The correct answer is A) Adrenaline. Dale's vasomotor reversal phenomenon refers to the phenomenon where, at low doses, adrenaline causes vasodilation through beta-2 adrenergic receptor activation, instead of vasoconstriction which is typically seen at higher doses through alpha-1 adrenergic receptors. This phenomenon is crucial in understanding the complex effects of catecholamines on the cardiovascular system. Option B) Noradrenaline predominantly acts on alpha-1 adrenergic receptors, leading to vasoconstriction. Option C) Isoprenaline is a non-selective beta-adrenergic receptor agonist, thus it does not exhibit the vasomotor reversal phenomenon seen with adrenaline. Educationally, understanding the vasomotor reversal phenomenon is essential for healthcare professionals, especially when prescribing drugs that manipulate the adrenergic system. It highlights the dose-dependent effects of catecholamines on blood vessels and underscores the importance of receptor selectivity in pharmacological actions. This knowledge is crucial in managing conditions where modulation of vascular tone is necessary, such as in hypertension or shock.

Correct Answer: D

Rationale: The correct answer is D) Redistribution to body tissues outside the CNS. Thiopentone sodium is an ultra-short-acting barbiturate commonly used for induction of anesthesia due to its rapid onset and short duration of action. The reason for the rapid clearance of its sedative effects is its redistribution to body tissues outside the central nervous system (CNS). Option A) Rapid hepatic metabolism is not the primary reason for the ultra-short duration of action of thiopentone sodium. While metabolism does play a role, rapid redistribution is the key factor. Option B) Rapid renal clearance is also not the primary reason for the drug's short duration of action. Thiopentone sodium is mainly eliminated by hepatic metabolism and redistribution. Option C) Extensive binding to plasma proteins would actually prolong the drug's effects rather than contribute to its ultra-short duration of action. In an educational context, understanding the pharmacokinetics of CNS drugs like thiopentone sodium is crucial for healthcare professionals, particularly anesthesiologists. Knowing how drugs are metabolized, cleared, and distributed can help in optimizing dosing regimens, anticipating drug interactions, and managing adverse effects effectively. It is important to grasp the mechanisms underlying drug actions to ensure safe and effective patient care.

Correct Answer: A

Rationale: In the context of CNS drugs pharmacology, understanding the specific characteristics of H1 receptor antagonists is crucial. In this question, the correct answer is A) Diphenhydramine. Diphenhydramine is a first-generation H1 receptor antagonist known for its high anticholinergic activity. This means that it has a strong affinity for blocking the muscarinic acetylcholine receptors, leading to common side effects such as dry mouth, blurred vision, constipation, and urinary retention. Terfenadine (option B) is a second-generation H1 receptor antagonist known for its non-sedating properties and lacks significant anticholinergic activity. Mepyramine (option C) and Clemastine (option D) are first-generation antihistamines but do not exhibit as high anticholinergic activity as Diphenhydramine. In an educational context, this question highlights the importance of understanding the diverse pharmacological properties of H1 receptor antagonists and their clinical implications. It emphasizes the need for healthcare professionals to be aware of the specific side effect profiles of different drugs to make informed decisions in patient care.

Correct Answer: C

Rationale: The correct answer is C) It is probably the drug of choice in the treatment of arrhythmias caused by digitalis intoxication. Phenytoin is known to be effective in treating arrhythmias caused by digitalis intoxication due to its ability to increase intracellular calcium levels, which helps counteract the effects of digitalis on cardiac conduction. This makes it a suitable choice in such cases. Option A is incorrect because phenytoin actually decreases the action potential duration in Purkinje fibers. Option B is incorrect as phenytoin has a long half-life of around 24 hours, resulting in a sustained duration of action. Option D is incorrect as phenytoin does not markedly depress conduction velocity in the A-V node and intraventricular conduction system. In an educational context, understanding the specific effects of phenytoin on cardiac conduction and its role in managing arrhythmias caused by digitalis intoxication is crucial for healthcare professionals, especially those involved in cardiovascular care or pharmacology. This knowledge ensures appropriate drug selection and safe, effective patient management.