Central Nervous System Pharmacology — MCQs

Central Nervous System Pharmacology Indian Medical PG Practice Questions and MCQs

Question 601: A potent and short-acting benzodiazepine was given to a patient for the purpose of causing hypnosis, but the drug caused psychiatric disturbances. Which of the following could be the hypnotic used?

A. Flurazepam
B. Nitrazepam
C. Temazepam
D. Triazolam (Correct Answer)

Explanation: **Explanation:** The correct answer is **Triazolam (Option D)**. **Why Triazolam is correct:** Triazolam is an ultra-short-acting benzodiazepine (BZD) with a rapid onset of action, making it highly effective for inducing sleep (hypnosis). However, its high potency and short half-life (2–4 hours) are associated with a unique side effect profile. As the drug levels drop rapidly before the next dose, patients often experience **rebound insomnia** and **daytime anxiety**. More significantly, Triazolam is notorious for causing **psychiatric disturbances**, including anterograde amnesia, agitation, confusion, and even hallucinations or "triazolam psychosis." Due to these adverse effects, it has been banned or restricted in several countries. **Analysis of Incorrect Options:** * **A. Flurazepam:** This is a long-acting BZD. Its active metabolites have a very long half-life (up to 100 hours), leading to "hangover" effects and cumulative sedation rather than acute psychiatric disturbances. * **B. Nitrazepam:** An intermediate-acting BZD commonly used for insomnia. While it can cause morning drowsiness, it is not specifically associated with the acute psychiatric reactions seen with Triazolam. * **C. Temazepam:** An intermediate-acting BZD. It is metabolized by conjugation (Phase II) and lacks active metabolites, making it safer for the elderly, but it does not fit the profile of a "potent, short-acting" drug causing behavioral disturbances. **High-Yield Clinical Pearls for NEET-PG:** * **Shortest acting BZD:** Midazolam (used for anesthesia/procedures) and Triazolam (used for hypnosis). * **Longest acting BZD:** Flurazepam and Diazepam. * **BZDs safe in liver failure (LOT):** **L**orazepam, **O**xazepam, **T**emazepam (undergo direct glucuronidation). * **Antidote for BZD overdose:** Flumazenil (competitive antagonist at the GABA-A receptor).

Question 602: Selegiline is:

A. Dopa decarboxylase inhibitor
B. MAO-B inhibitor (Correct Answer)
C. COMT inhibitor
D. MAO-A inhibitor

Explanation: **Explanation:** **1. Why Option B is Correct:** Selegiline is a **selective, irreversible inhibitor of Monoamine Oxidase-B (MAO-B)**. In the brain, MAO-B is the primary enzyme responsible for the oxidative metabolism of dopamine. By inhibiting this enzyme, Selegiline increases the concentration and prolongs the action of dopamine in the nigrostriatal pathway. At therapeutic doses, it does not interfere with the metabolism of other amines like norepinephrine or serotonin, making it a mainstay in the management of **Parkinson’s Disease**. **2. Why Other Options are Incorrect:** * **Option A (Dopa decarboxylase inhibitor):** These drugs, such as **Carbidopa** and **Benserazide**, inhibit the peripheral conversion of L-Dopa to dopamine, reducing systemic side effects and increasing CNS bioavailability. * **Option C (COMT inhibitor):** Drugs like **Entacapone** and **Tolcapone** inhibit Catechol-O-methyltransferase. They are used as adjuncts to L-Dopa to prevent its peripheral (Entacapone) or central (Tolcapone) degradation. * **Option D (MAO-A inhibitor):** MAO-A primarily metabolizes norepinephrine and serotonin. Inhibitors like **Moclobemide** are used as antidepressants. Non-selective MAO inhibitors (inhibiting both A and B) are associated with the "Cheese Reaction." **3. High-Yield Clinical Pearls for NEET-PG:** * **Selectivity Loss:** At high doses, Selegiline loses its selectivity and inhibits MAO-A, potentially leading to hypertensive crises if tyramine-rich foods are consumed. * **Neuroprotection:** Selegiline is hypothesized to have neuroprotective effects by reducing free radical formation during dopamine metabolism. * **Metabolism:** It is metabolized into **amphetamine and methamphetamine**, which may cause insomnia if taken late in the day. * **Rasagiline:** A newer, more potent, irreversible MAO-B inhibitor that is not metabolized into amphetamine derivatives.

Question 603: Which of the following drugs is used as a transdermal patch for Parkinson's disease?

A. Levodopa
B. Rotigotine (Correct Answer)
C. Selegiline
D. Carbidopa

Explanation: Rotigotine is a non-ergot dopamine agonist (specifically acting on D3, D2, and D1 receptors). It is unique because it is formulated as a **transdermal patch** designed for once-daily application. This delivery system provides continuous drug delivery (continuous dopaminergic stimulation), which helps maintain stable plasma levels and reduces the "off" periods associated with fluctuating levels of oral medications.Analysis of Incorrect Options: * **Levodopa (A):** The gold standard for Parkinson’s, but it is administered orally (often with carbidopa) [1] or as an intestinal gel (Duopa). It is not available as a patch due to its high dosage requirements and transport characteristics. * **Selegiline (C):** While Selegiline is available as a transdermal patch (Emsam), it is FDA-approved in that form specifically for **Major Depressive Disorder**, not Parkinson’s disease. For Parkinson's, it is used orally as an MAO-B inhibitor. * **Carbidopa (D):** This is a peripheral dopa-decarboxylase inhibitor used solely to prevent the peripheral metabolism of Levodopa. It has no antiparkinsonian effect on its own and is not used as a patch.High-Yield Clinical Pearls for NEET-PG: * **Dopamine Agonists:** Rotigotine, Pramipexole, and Ropinirole are preferred in younger patients to delay the start of Levodopa. * **Side Effects:** Like other dopamine agonists, Rotigotine can cause impulse control disorders (pathological gambling, hypersexuality) [1, 2] and sudden sleep attacks. * **Apomorphine:** Another non-oral dopamine agonist, used via subcutaneous injection for "rescue" therapy during acute off-episodes. * **Patch Site:** Rotigotine patches should be rotated daily to avoid skin irritation; the same site should not be used more than once every 14 days.

Question 604: Which drug has been found to be beneficial in amyotrophic lateral sclerosis?

A. Riluzole (Correct Answer)
B. Methylprednisolone
C. Hydroxyurea
D. None of the above

Explanation: **Explanation:** **Amyotrophic Lateral Sclerosis (ALS)** is a progressive neurodegenerative disease involving both upper and lower motor neurons. The pathogenesis is linked to **glutamate excitotoxicity**, where excessive glutamate leads to overstimulation of NMDA receptors, resulting in neuronal calcium overload and cell death. **Why Riluzole is the Correct Answer:** **Riluzole** is a glutamate antagonist. It works by: 1. Inhibiting presynaptic glutamate release. 2. Inactivating voltage-dependent sodium channels. 3. Interfering with intracellular events following transmitter binding. Clinical trials have shown that Riluzole modestly prolongs survival (by approximately 2–3 months) and delays the need for tracheostomy in ALS patients. **Why the Other Options are Incorrect:** * **B. Methylprednisolone:** While inflammation occurs in ALS, corticosteroids like methylprednisolone have shown no clinical benefit in slowing disease progression. They are primarily used in acute relapses of Multiple Sclerosis. * **C. Hydroxyurea:** This is a ribonucleotide reductase inhibitor used in Sickle Cell Anemia (to increase HbF) and Chronic Myeloid Leukemia. It has no role in treating motor neuron diseases. **High-Yield Clinical Pearls for NEET-PG:** * **Edaravone:** Another FDA-approved drug for ALS; it acts as a **free radical scavenger** (antioxidant) to reduce oxidative stress. * **Side effects of Riluzole:** Most common are nausea, weakness, and **elevated liver enzymes** (ALT/AST), necessitating regular LFT monitoring. * **Symptomatic Management in ALS:** * Spasticity: Baclofen or Tizanidine. * Sialorrhea (Drooling): Glycopyrrolate or Atropine.

Question 605: Which of the following is not a known side effect of clozapine?

A. Agranulocytosis
B. Seizures
C. Sialosis
D. Weight loss (Correct Answer)

Explanation: **Explanation:** Clozapine is a prototype **Atypical (Second-Generation) Antipsychotic** used primarily for treatment-resistant schizophrenia. The correct answer is **Weight loss**, as clozapine is actually notorious for causing significant **weight gain** and metabolic dysregulation. **Why Weight Loss is Incorrect (The Correct Answer):** Clozapine has a high affinity for **H1 (histamine)** and **5-HT2C (serotonin)** receptors. Blockade of these receptors leads to increased appetite and sedation, resulting in profound weight gain, hyperlipidemia, and an increased risk of Type 2 Diabetes Mellitus. **Analysis of Incorrect Options (Known Side Effects):** * **A. Agranulocytosis:** This is the most dreaded side effect (occurring in ~1% of patients). It requires mandatory weekly hematological monitoring (ANC counts) for the first six months of therapy. * **B. Seizures:** Clozapine reduces the seizure threshold in a dose-dependent manner. It carries the highest risk of seizures among all antipsychotics (approx. 5% at doses >600mg/day). * **C. Sialosis (Sialorrhea):** Paradoxically, despite its anticholinergic profile, clozapine causes excessive salivation (wet pillow syndrome), likely due to M4 receptor agonism or impairment of the swallowing reflex. **High-Yield Clinical Pearls for NEET-PG:** * **Drug of Choice:** Treatment-resistant schizophrenia and suicidal behavior in schizophrenia. * **Myocarditis:** A rare but fatal idiosyncratic reaction; monitor for chest pain or dyspnea in the first month. * **No EPS:** Clozapine has the lowest risk of Extrapyramidal Side Effects (EPS) and virtually zero risk of Tardive Dyskinesia. * **Lacks Prolactin Elevation:** Unlike most antipsychotics, it does not cause hyperprolactinemia.

Question 606: Which of the following adverse effects is characteristically associated with methysergide?

A. Pulmonary hypertension
B. Retroperitoneal fibrosis (Correct Answer)
C. Hepatotoxicity
D. Ischemic heart disease

Explanation: **Explanation:** **Methysergide** is an ergot alkaloid and a potent 5-HT₂ receptor antagonist formerly used for the prophylaxis of migraine and cluster headaches. **Why Retroperitoneal Fibrosis is Correct:** The most characteristic and serious adverse effect of long-term methysergide therapy is **retroperitoneal fibrosis**. This condition involves the proliferation of dense fibrous tissue in the retroperitoneum, which can obstruct the ureters, leading to hydronephrosis and renal failure. It is also associated with similar fibrotic changes in the pleura (**pleuropulmonary fibrosis**) and the endocardium (**subendocardial fibrosis/valvular heart disease**). The mechanism is thought to be related to its serotonergic activity, which can stimulate fibroblast proliferation. **Analysis of Incorrect Options:** * **A. Pulmonary hypertension:** While some serotonergic drugs (like fenfluramine) are linked to pulmonary hypertension, methysergide is specifically known for pleuropulmonary fibrosis rather than primary vascular hypertension. * **C. Hepatotoxicity:** Methysergide is not typically associated with significant liver injury; its toxicity profile is dominated by fibrotic and vascular complications. * **D. Ischemic heart disease:** While ergot alkaloids can cause vasoconstriction, the "hallmark" chronic toxicity of methysergide is fibrosis, not acute coronary syndrome. **High-Yield Clinical Pearls for NEET-PG:** 1. **Drug Holidays:** To prevent fibrotic complications, methysergide requires a mandatory "drug-free interval" of 3–4 weeks every 6 months. 2. **Withdrawal:** It must be tapered slowly to avoid rebound headaches. 3. **Current Status:** Due to these severe fibrotic risks, methysergide has been largely replaced by safer alternatives like Beta-blockers, Topiramate, or Valproate.

Question 607: A patient is prescribed a first-generation antihistamine. What should they be advised to avoid?

A. Driving a motor vehicle (Correct Answer)
B. Consuming cheese
C. Engaging in strenuous physical exercise
D. All of the above

Explanation: **Explanation:** **1. Why Option A is Correct:** First-generation antihistamines (e.g., Diphenhydramine, Chlorpheniramine, Promethazine) are highly **lipophilic** and readily cross the **blood-brain barrier (BBB)**. Once in the CNS, they antagonize H1 receptors, which are essential for maintaining wakefulness and alertness. This results in significant **sedation**, drowsiness, and impaired psychomotor performance. Patients are strictly advised to avoid driving or operating heavy machinery to prevent accidents due to delayed reaction times. **2. Why Other Options are Incorrect:** * **Option B (Cheese):** Avoiding tyramine-rich foods like aged cheese is a specific precaution for patients on **MAO inhibitors** (to prevent hypertensive crisis), not antihistamines. * **Option C (Strenuous Exercise):** While antihistamines have mild anticholinergic effects that can slightly decrease sweating, there is no absolute contraindication for exercise. This precaution is more relevant for drugs causing severe heat intolerance or significant beta-blockade. **3. NEET-PG High-Yield Clinical Pearls:** * **Mechanism of Sedation:** First-generation H1 blockers are non-selective and have high affinity for central H1 receptors. Second-generation agents (e.g., Cetirizine, Loratadine) are polar, have low lipid solubility, and are substrates for **P-glycoprotein efflux pumps**, making them "non-sedating." * **Anticholinergic Side Effects:** First-generation agents also block muscarinic receptors, leading to "dry" symptoms: dry mouth, blurred vision, urinary retention, and constipation. * **Paradoxical Excitation:** In children, toxic doses of these drugs can sometimes cause CNS stimulation and seizures rather than sedation. * **Drug Interaction:** They potentiate the effects of other CNS depressants, including alcohol and benzodiazepines.

Question 608: Varenicline is used in which of the following conditions?

A. Pulmonary hemosiderosis
B. Sleep apnea
C. Alpha-1-antitrypsin deficiency
D. Nicotine dependency (Correct Answer)

Explanation: **Varenicline** is a high-yield drug in CNS pharmacology, specifically used as a first-line pharmacotherapy for **smoking cessation (Nicotine dependency)**. ### 1. Why Nicotine Dependency is Correct Varenicline acts as a **selective partial agonist** at the **α4β2 nicotinic acetylcholine receptors (nAChR)** in the brain. Its mechanism of action is twofold: * **Agonist effect:** It stimulates the receptor to release low levels of dopamine, which helps reduce withdrawal symptoms and cravings. * **Antagonist effect:** Because it occupies the receptor with high affinity, it prevents inhaled nicotine from binding. This "blocks" the reward/reinforcement pathway, making smoking less satisfying if the patient relapses. ### 2. Why Other Options are Incorrect * **A. Pulmonary hemosiderosis:** This is a rare lung disease characterized by alveolar hemorrhage. Treatment typically involves immunosuppressants (like corticosteroids) or managing underlying causes (like mitral stenosis). * **B. Sleep apnea:** Obstructive sleep apnea is primarily managed with CPAP (Continuous Positive Airway Pressure) or weight loss. Central sleep apnea may involve drugs like Acetazolamide, but not Varenicline. * **C. Alpha-1-antitrypsin deficiency:** This genetic condition leads to emphysema and liver disease. Management involves IV augmentation therapy with purified human AAT and bronchodilators. ### 3. NEET-PG High-Yield Clinical Pearls * **Side Effects:** The most common side effect is **nausea** (dose-dependent). It is also associated with **insomnia and vivid/abnormal dreams**. * **Black Box Warning (Historical):** Previously, it carried a warning for neuropsychiatric events (suicidal ideation, depression), though recent studies (EAGLES trial) suggest this risk is lower than initially feared. * **Comparison:** Unlike **Bupropion** (another smoking cessation drug), Varenicline does not significantly affect the reuptake of norepinephrine or dopamine; its action is direct receptor modulation. * **Excretion:** It is primarily excreted unchanged by the kidneys; thus, dose adjustment is required in **renal failure**.

Question 609: Which of the following antiepileptic drugs acts by opening potassium channels?

A. Ezogabine (Correct Answer)
B. Felbamate
C. Lacosamide
D. Gabapentin

Explanation: **Explanation:** **Correct Answer: A. Ezogabine (Retigabine)** Ezogabine (known as Retigabine in Europe) has a unique mechanism of action among antiepileptics. It acts as a **positive allosteric modulator of KCNQ2-5 (Kv7.2–7.5) voltage-gated potassium channels**. By opening these channels, it facilitates an outward potassium current (the "M-current"), which stabilizes the resting membrane potential and hyperpolarizes the neuron, thereby reducing repetitive firing and neuronal excitability. **Analysis of Incorrect Options:** * **B. Felbamate:** Primarily acts by blocking **NMDA receptors** (glutamate) and modulating GABA-A receptors. It is reserved for refractory epilepsy due to risks of aplastic anemia and hepatic failure. * **C. Lacosamide:** Acts by enhancing the **slow inactivation of voltage-gated sodium channels**, unlike traditional sodium channel blockers (like Phenytoin) which affect fast inactivation. * **D. Gabapentin:** Despite its name, it does not act on GABA receptors. It binds to the **α2δ-1 subunit of voltage-gated calcium channels**, reducing the release of excitatory neurotransmitters. **High-Yield Facts for NEET-PG:** * **Ezogabine Side Effects:** A unique "blue-man" presentation—it can cause **blue skin discoloration** and **retinal pigmentation** (requires regular ophthalmological monitoring). * **Lacosamide:** Often tested for its "slow inactivation" mechanism and its lack of significant drug-drug interactions. * **Broad-spectrum vs. Narrow-spectrum:** Remember that drugs affecting potassium channels or multiple mechanisms (like Valproate/Topiramate) often have broad-spectrum activity.

Question 610: Ropinirole is most useful for the treatment of which condition?

A. Parkinson's disease (Correct Answer)
B. Wilson's disease
C. Hoffmann syndrome
D. Carpal tunnel syndrome

Explanation: **Explanation:** **Ropinirole** is a non-ergoline **Dopamine Agonist** that acts selectively on D2 and D3 receptors. In **Parkinson’s disease**, there is a progressive loss of dopaminergic neurons in the substantia nigra. Ropinirole bypasses these degenerating neurons to directly stimulate postsynaptic dopamine receptors in the striatum, thereby improving motor symptoms like bradykinesia and rigidity. It is used both as monotherapy in early Parkinson's (to delay the use of Levodopa) and as an adjunct in advanced stages. **Analysis of Incorrect Options:** * **Wilson’s Disease:** This is a disorder of copper metabolism. Treatment involves copper chelators like **D-Penicillamine** or Trientine, and Zinc to prevent absorption. * **Hoffmann Syndrome:** This is a specific form of hypothyroid myopathy characterized by muscle stiffness and pseudohypertrophy. The treatment is **Thyroxine replacement**. * **Carpal Tunnel Syndrome:** This is a compression neuropathy of the median nerve. Management includes splinting, NSAIDs, corticosteroid injections, or surgical decompression. **High-Yield Clinical Pearls for NEET-PG:** * **Restless Leg Syndrome (RLS):** Ropinirole and Pramipexole are the first-line FDA-approved treatments for RLS. * **Side Effects:** A unique and high-yield side effect of dopamine agonists (Ropinirole/Pramipexole) is **impulse control disorders** (e.g., pathological gambling, hypersexuality) and **sudden sleep attacks**. * **Non-ergot vs. Ergot:** Unlike older ergot derivatives (Bromocriptine), Ropinirole does not cause cardiac valvular fibrosis or pleuropulmonary fibrosis.

Practice by Chapter

General Anesthetics

Practice Questions

Local Anesthetics

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Sedative-Hypnotics

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Antiepileptic Drugs

Practice Questions

Antiparkinsonian Drugs

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Opioid Analgesics

Practice Questions

Drugs of Abuse and Addiction

Practice Questions

Psychostimulants

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Hallucinogens

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CNS Stimulants and Cognitive Enhancers

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