Central Nervous System Pharmacology — MCQs

Central Nervous System Pharmacology Indian Medical PG Practice Questions and MCQs

Question 891: Which one of the following is a 5-HT3 antagonist?

A. Ondansetron (Correct Answer)
B. Clozapine
C. Ergotamine
D. Orlistat

Explanation: ***Ondansetron*** - **Ondansetron** is a highly effective **5-HT3 receptor antagonist** primarily used as an antiemetic, particularly for chemotherapy-induced nausea and vomiting. - It works by blocking serotonin's action on 5-HT3 receptors in the **chemoreceptor trigger zone** and the **gastrointestinal tract**, thereby preventing the emetic reflex. *Orlistat* - **Orlistat** is a medication used for **weight loss** that acts as a **gastrointestinal lipase inhibitor**. - It prevents the absorption of dietary fats by inhibiting enzymes in the gut, rather than affecting serotonin receptors. *Clozapine* - **Clozapine** is an **atypical antipsychotic** medication used primarily in the treatment of **schizophrenia** that is unresponsive to other drugs. - While it has a complex pharmacology involving multiple receptors, its primary mechanism does not involve blocking 5-HT3 receptors. *Ergotamine* - **Ergotamine** is an **ergot alkaloid** primarily used for the treatment of **migraines**. - Its mechanism of action involves partial agonist and antagonist effects on various serotonin, dopamine, and alpha-adrenergic receptors, but it is not a selective 5-HT3 antagonist.

Question 892: The use of levodopa is avoided in which of the following patients?

A. Amyotrophic lateral sclerosis
B. Psychosis (Correct Answer)
C. Alzheimer's disease
D. Essential tremor

Explanation: ***Psychosis*** - Levodopa increases **dopaminergic activity** in the brain, which can significantly worsen or induce **psychotic symptoms** like hallucinations and delusions. - Patients with pre-existing psychosis or a history of psychotic episodes are at high risk, making levodopa a **contraindicated** treatment. *Alzheimer's disease* - While Alzheimer's patients may experience motor symptoms, levodopa is generally not avoided unless there are specific **parkinsonian features** responsive to dopamine. - The primary symptoms of Alzheimer's are **cognitive decline**, which levodopa does not treat and could potentially worsen agitation or confusion in advanced stages. *Amyotrophic lateral sclerosis* - **ALS** is a progressive neurodegenerative disease affecting motor neurons, leading to muscle weakness and atrophy. - Levodopa is **not effective** in treating ALS because the disease pathology does not involve dopamine deficiency. *Essential tremor* - Essential tremor is a movement disorder primarily treated with **beta-blockers** or **anti-seizure medications**. - Levodopa has **no established efficacy** in treating essential tremor, and its use is unrelated to its pathophysiology.

Question 893: Which of the following is not a treatment option for patients with relapsing-remitting multiple sclerosis?

A. IFN-β1b
B. IFN-β1a
C. Glatiramer acetate
D. Cyclophosphamide (Correct Answer)

Explanation: ***Cyclophosphamide*** - This is an **immunosuppressant** primarily used in severe autoimmune conditions or certain cancers, not a standard maintenance treatment for **relapsing-remitting multiple sclerosis (RRMS)**. - While it has been explored for severe, rapidly worsening MS, it is not considered a first-line or common treatment option for RRMS due to its significant toxicity and side effect profile. *IFN-β1b* - **Interferon beta-1b** is a well-established **disease-modifying therapy** for RRMS, shown to reduce the frequency and severity of relapses. - It works by modulating the immune system to decrease inflammation and demyelination in the central nervous system. *IFN-β1a* - **Interferon beta-1a** (both intramuscular and subcutaneous formulations) is also a widely used **disease-modifying therapy** for RRMS. - Similar to interferon beta-1b, it helps to reduce relapse rates and slow the progression of disability in patients with RRMS. *Glatiramer acetate* - This is another common **disease-modifying therapy** for RRMS, which acts as a "decoy" myelin basic protein. - It works by inducing **T-cell anergy** and shifting the immune response from pro-inflammatory to anti-inflammatory, reducing attacks on myelin.

Question 894: Acute opioid withdrawal is characterized by which of the following symptoms?

A. Rhinorrhea, Piloerection, Miosis
B. Rhinorrhea, Piloerection, Insomnia (Correct Answer)
C. Rhinorrhea, Piloerection, Constipation
D. Insomnia, Constipation

Explanation: ***Rhinorrhea, Piloerection, Insomnia*** - **Rhinorrhea** (runny nose) and **piloerection** (goosebumps) are classic autonomic signs of opioid withdrawal, often described as "cold turkey." - **Insomnia** is a common and distressing symptom of opioid withdrawal, reflecting the hyperactivity of the central nervous system. *Rhinorrhea, Piloerection, Miosis* - While **rhinorrhea** and **piloerection** are characteristic of opioid withdrawal, **miosis** (pupil constriction) is a symptom of **opioid intoxication**, not withdrawal. - Opioid withdrawal typically causes **mydriasis** (pupil dilation) due to sympathetic overactivity. *Rhinorrhea, Piloerection, Constipation* - **Rhinorrhea** and **piloerection** are correct signs of opioid withdrawal. However, **constipation** is a well-known side effect of **opioid use** itself, not a symptom of opioid withdrawal. - Opioid withdrawal more commonly presents with **diarrhea** as gastrointestinal motility increases. *Insomnia, Constipation* - **Insomnia** is a symptom of opioid withdrawal, but **constipation** is not; rather, it is associated with opioid use. - This option also omits other key withdrawal symptoms such as **rhinorrhea** and **piloerection**.

Question 895: What is the most common side effect of haloperidol?

A. Hypotension
B. Dryness of mouth
C. Tic disorder
D. Akathisia (Correct Answer)

Explanation: ***Akathisia*** - **Akathisia** is one of the **most common extrapyramidal symptoms (EPS)** associated with haloperidol, occurring in **20-75% of patients**. - It is characterized by a feeling of **inner restlessness** and an **inability to stay still**, often manifesting as pacing, rocking, or shifting weight. - Haloperidol, a high-potency **first-generation antipsychotic**, has a high propensity to cause EPS, including akathisia, due to its **strong dopamine D2 receptor blockade** in the nigrostriatal pathway. - Along with drug-induced parkinsonism, akathisia is among the most frequently encountered side effects with haloperidol use. *Hypotension* - While orthostatic hypotension can occur with antipsychotics, particularly those with strong **alpha-1 adrenergic blockade** (e.g., lower potency first-generation antipsychotics like chlorpromazine, or some second-generation antipsychotics), it is not the most common side effect of haloperidol. - Haloperidol has relatively **weak alpha-1 blocking activity** compared to other antipsychotics. *Dryness of mouth* - **Dryness of mouth (xerostomia)** is a common anticholinergic side effect of some antipsychotics, but it is not the most common or prominent side effect of haloperidol. - Haloperidol has relatively **weak anticholinergic activity** compared to lower potency antipsychotics. *Tic disorder* - **Tic disorders** are characterized by sudden, rapid, recurrent, nonrhythmic motor movements or vocalizations. - While haloperidol can be used to **treat severe tics** (e.g., in Tourette syndrome), it is not a common side effect of the medication itself; rather, it is a condition that antipsychotics like haloperidol may target therapeutically.

Question 896: What is the preferred first-line treatment for a young patient (under 65 years) newly diagnosed with Parkinson's disease?

A. MAO-B inhibitor
B. Amantadine
C. Dopamine agonist (Correct Answer)
D. Levodopa

Explanation: ***Dopamine agonist*** - For younger patients (typically under 65-70 years) with Parkinson's disease, **dopamine agonists** (e.g., pramipexole, ropinirole) are traditionally preferred as initial therapy to delay the introduction of levodopa. - This approach aims to reduce the risk of **motor complications** (e.g., dyskinesias, motor fluctuations) associated with long-term levodopa use. - This represents the **classical treatment strategy** commonly taught for medical examinations, though current clinical practice increasingly emphasizes individualized treatment decisions. *Levodopa* - While the **most effective symptomatic treatment** for Parkinson's disease, levodopa is traditionally reserved for older patients or those with more severe symptoms requiring greater symptomatic control. - Long-term use of levodopa, especially when started young, has been associated with **motor complications** like dyskinesia and wearing-off phenomena. - However, levodopa provides superior quality of life benefits and remains the gold standard for motor symptom control. *MAO-B inhibitor* - **MAO-B inhibitors** (e.g., selegiline, rasagiline) offer **mild symptomatic benefit** and may have neuroprotective properties. - Their efficacy for significant motor symptoms is less than dopamine agonists or levodopa. - They are often used as **adjunct therapy** or in very early disease with mild symptoms, not typically as first-line monotherapy for managing primary motor symptoms in younger patients. *Amantadine* - **Amantadine** is primarily used to relieve **levodopa-induced dyskinesia** in later stages of Parkinson's disease. - It also has mild symptomatic benefit for tremor and rigidity but is **not a first-line agent** due to weaker efficacy compared to dopamine agonists. - Side effects include livedo reticularis and confusion, particularly in elderly patients.

Question 897: Adverse effects of phenytoin include the following EXCEPT:

A. Ataxia
B. Hirsutism
C. Hypercalcemia (Correct Answer)
D. Lymphadenopathy

Explanation: ***Hypercalcemia*** - Phenytoin can actually lead to **hypocalcemia** due to its effect on vitamin D metabolism, increasing its degradation and leading to osteomalacia or rickets [1]. - Therefore, **hypercalcemia** is not an expected adverse effect of phenytoin use. *Lymphadenopathy* - **Generalized lymphadenopathy** is a known, though less common, adverse effect of phenytoin, sometimes mimicking lymphoma. - It's part of a broader hypersensitivity reaction that can occur with the drug. *Ataxia* - **Ataxia** is a common dose-dependent adverse effect of phenytoin, especially at higher therapeutic or toxic levels [1], [2]. - It manifests as impaired coordination and balance due to cerebellar dysfunction [1]. *Hirsutism* - **Hirsutism**, or excessive hair growth, is a well-known chronic side effect of phenytoin [1]. - This effect is more aesthetically concerning than medically dangerous and is particularly common in young women [1].

Question 898: Which of the following is a pure opioid antagonist?

A. Naloxone (Correct Answer)
B. Buprenorphine
C. Pentazocine
D. Morphine

Explanation: ***Naloxone*** - **Naloxone** is a pure opioid antagonist that rapidly reverses the effects of opioid agonists by competing for opioid receptor binding sites [1,2]. - It has a high affinity for μ-opioid receptors and acts as a competitive antagonist [1], making it clinically useful for treating **opioid overdose**. *Buprenorphine* - **Buprenorphine** is a **partial opioid agonist** at the μ-opioid receptor and an antagonist at the κ-opioid receptor [4]. - It can precipitate withdrawal in opioid-dependent individuals if administered while full agonists are present due to its partial agonistic activity. *Pentazocine* - **Pentazocine** is a **mixed opioid agonist-antagonist**, acting as a partial agonist or antagonist at μ-opioid receptors and an agonist at κ-opioid receptors. - Its effects can vary, including analgesia (kappa agonism) and potential for withdrawal symptoms in opioid-dependent individuals (mu antagonism). *Morphine* - **Morphine** is a potent **full opioid agonist** that primarily acts on μ-opioid receptors, producing analgesia, sedation, and euphoria [3]. - It does not block opioid receptors; instead, it activates them, leading to its therapeutic and adverse effects.

Question 899: Which of these anticonvulsants causes a contraction of the visual field?

A. Levetiracetam
B. Phenytoin
C. Vigabatrin (Correct Answer)
D. Ethosuximide

Explanation: ***Vigabatrin*** - **Vigabatrin** is known to cause **irreversible concentric visual field constriction** in a significant percentage of patients, often leading to a permanent reduction in peripheral vision. - This adverse effect, often termed Vigabatrin-associated Visual Field Defect (VAVFD), is due to its impact on the **retina** and is thought to involve GABAergic pathways in the visual system. *Levetiracetam* - **Levetiracetam** is generally well-tolerated and is not commonly associated with significant visual field defects. - Common side effects are primarily neurological, such as **somnolence**, **dizziness**, and **behavioral changes**. *Phenytoin* - **Phenytoin** is more likely to cause dose-related ocular side effects such as **nystagmus** (involuntary eye movements) and **diplopia** (double vision), rather than a contraction of the visual field. - Long-term use can also lead to **gingival hyperplasia** and **hirsutism**. *Ethosuximide* - **Ethosuximide** is primarily used for **absence seizures** and its common side effects are gastrointestinal (**nausea**, **vomiting**, **anorexia**) and neurological (**drowsiness**, **dizziness**, **headache**). - It does not typically cause visual field constriction, which is a rare and specific side effect of certain other anticonvulsants.

Question 900: Which of the following drugs is not suitable for the management of essential tremors?

A. Diazepam
B. Levodopa (Correct Answer)
C. Propranolol
D. Metoprolol

Explanation: ***Levodopa*** - **Levodopa** is primarily used to treat **Parkinson's disease**, specifically targeting its hallmark **bradykinesia** and **rigidity**, not essential tremor. - Its mechanism of action involves increasing dopamine levels in the brain, which is not an effective strategy for essential tremor, and it may even **exacerbate tremor** in some cases. *Diazepam* - **Diazepam**, a **benzodiazepine**, can be used as an adjunct in essential tremor management, particularly for patients experiencing significant **anxiety** that exacerbates their tremor. - It acts by enhancing the effect of **GABA**, leading to a calming effect and muscle relaxation, which can mildly reduce tremor severity. *Metoprolol* - **Metoprolol** is a **beta-blocker** that can be used for essential tremor, especially when **propranolol** is not tolerated or contraindicated. - It works by blocking beta-adrenergic receptors, which helps to reduce the physiological tremor component and is often effective for patients with a triggered or anxiety-related tremor. *Propranolol* - **Propranolol** is considered a **first-line treatment** for essential tremor due to its efficacy in reducing tremor amplitude, particularly in the hands. - It is a non-selective beta-blocker that reduces **sympathetic nervous system** overactivity, which contributes to tremor pathogenesis.

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General Anesthetics

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Local Anesthetics

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Drugs of Abuse and Addiction

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Psychostimulants

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Hallucinogens

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CNS Stimulants and Cognitive Enhancers

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