Sensitivity of a nerve fiber to blockade by lidocaine depends on

Correct Answer: D

Rationale: In understanding the sensitivity of a nerve fiber to blockade by lidocaine, it is crucial to consider both the myelination status and the internodal distances. The correct answer, option D, "Both (b) and (c)," is supported by the fact that myelinated fibers are more sensitive to lidocaine blockade compared to nonmyelinated fibers. This is due to the presence of a myelin sheath which accelerates the conduction velocity, making these fibers more susceptible to local anesthetics like lidocaine. Additionally, internodal distances play a role as longer internodal lengths increase the likelihood of successful blockade. Option A, "Whether the fiber is sensory or motor," is incorrect because the sensitivity to lidocaine blockade is not primarily dependent on the fiber being sensory or motor but rather on its myelination status and internodal distances. Option C, "Internodal distances in the fiber," is only partially correct as it is a factor in sensitivity but not the sole determinant. In an educational context, this question highlights the importance of understanding the physiological and anatomical factors that influence the response of nerve fibers to pharmacological interventions. It underscores the need for healthcare professionals to have a comprehensive grasp of how different nerve fibers react to medications like lidocaine, which is crucial in clinical practice when administering local anesthesia or managing pain.

Correct Answer: D

Rationale: Bisphosphonates are a class of drugs commonly used to treat osteoporosis by inhibiting bone resorption. The correct answer, option D, "Postmenopausal osteoporosis," is the appropriate indication for bisphosphonate use. Postmenopausal women are at an increased risk of osteoporosis due to hormonal changes that lead to bone density loss, making bisphosphonates an effective treatment to prevent fractures and maintain bone health. Option A, "Organophosphate poisoning," is incorrect because bisphosphonates are not indicated for this condition. Organophosphate poisoning is typically managed with antidotes like atropine and pralidoxime. Option B, "Dementia," is also incorrect as bisphosphonates do not have a role in the treatment of dementia. Dementia is a neurodegenerative condition that requires specific therapies targeting cognitive function. Option C, "Steven's Johnson syndrome," is an incorrect choice as bisphosphonates are not indicated for this severe skin reaction. Steven's Johnson syndrome is managed through supportive care and discontinuation of the offending agent. In an educational context, understanding the appropriate indications for drugs like bisphosphonates is crucial for healthcare professionals, especially those specializing in pharmacology. This knowledge ensures safe and effective medication management, leading to improved patient outcomes. By grasping the rationale behind drug indications, students can make informed decisions in clinical practice and provide evidence-based care to their patients.

Correct Answer: B

Rationale: In the context of CNS Drugs Pharmacology, understanding the anesthetic action of thiopentone sodium is crucial for healthcare professionals. The correct answer, B) Poor analgesia, reflects the pharmacological profile of thiopentone sodium as a potent intravenous anesthetic with minimal analgesic properties. Thiopentone sodium primarily acts as a CNS depressant by enhancing the inhibitory actions of GABA, leading to sedation and hypnosis. However, it lacks significant analgesic effects, making it unsuitable as a standalone analgesic agent. Option A) Good muscle relaxation is incorrect because thiopentone sodium does not directly induce muscle relaxation. Muscle relaxation is typically achieved through the administration of neuromuscular blocking agents in anesthesia practice. Educationally, this question highlights the specific pharmacological actions of thiopentone sodium, emphasizing the importance of selecting appropriate anesthetic agents based on their unique properties. Healthcare providers need to be knowledgeable about the mechanism of action of CNS drugs to ensure safe and effective patient care during anesthesia procedures.

Correct Answer: C

Rationale: In the context of CNS drugs pharmacology, it is crucial to understand the mechanisms of drug action and elimination to ensure safe and effective pharmacotherapy. In the case of phenobarbital, the major process that terminates its action is hepatic metabolism, making option C the correct answer. Phenobarbital is primarily metabolized in the liver through hepatic microsomal enzymes, particularly the cytochrome P450 system. This metabolism leads to the conversion of phenobarbital into inactive metabolites, which are then excreted from the body. Therefore, hepatic metabolism is essential in eliminating phenobarbital from the system, thus terminating its pharmacological effects. Option A, biliary excretion, is not the major route of elimination for phenobarbital. While some drugs undergo biliary excretion, it is not the primary mechanism for phenobarbital. Option B, renal excretion, is also not the primary route for phenobarbital elimination. Renal excretion is more important for drugs that are primarily eliminated unchanged through the kidneys. Option D, redistribution, is not a significant factor in terminating the action of phenobarbital. Redistribution refers to the movement of a drug from one site in the body to another and is not the primary mechanism for drug elimination. Understanding the major processes involved in drug metabolism and elimination is essential for healthcare professionals to make informed decisions about drug dosing, potential drug interactions, and adverse effects. This knowledge is fundamental in ensuring the safe and effective use of CNS drugs like phenobarbital in clinical practice.

Correct Answer: B

Rationale: In this question, the correct answer is B) Sodium valproate. Sodium valproate displaces plasma protein-bound phenytoin and decreases its metabolism through inhibition of hepatic metabolizing enzymes. This interaction can lead to an increase in free phenytoin levels, potentially causing toxicity. Carbamazepine (A) is an enzyme inducer that can increase the metabolism of phenytoin, leading to decreased phenytoin levels. Cimetidine (C) inhibits hepatic microsomal enzymes, but it does not displace phenytoin from plasma proteins. Chloramphenicol (D) inhibits hepatic drug metabolism but does not displace phenytoin from plasma proteins. In an educational context, understanding drug interactions is crucial for healthcare professionals to ensure safe and effective pharmacotherapy. Knowledge of how drugs interact can help in predicting and preventing adverse effects and optimizing treatment outcomes for patients. It is essential to be aware of specific drug interactions, like the one between sodium valproate and phenytoin, to make informed clinical decisions and provide quality patient care.