Central Nervous System Pharmacology — MCQs

Central Nervous System Pharmacology Indian Medical PG Practice Questions and MCQs

Question 41: Which of the following SNRIs is used in the management of stress urinary incontinence?

A. Brofaromine
B. Citalopram
C. Nefazodone
D. Duloxetine (Correct Answer)

Explanation: **Explanation:** **Duloxetine** is a Serotonin-Norepinephrine Reuptake Inhibitor (SNRI) that plays a unique role in managing **Stress Urinary Incontinence (SUI)**. It works by increasing the levels of serotonin and norepinephrine at the Onuf’s nucleus in the sacral spinal cord. This leads to increased stimulation of the pudendal nerve, which enhances the contraction of the **external urethral sphincter** (striated muscle), thereby increasing urethral resistance and preventing leakage during physical stress (like coughing or sneezing). **Analysis of Incorrect Options:** * **A. Brofaromine:** This is a Selective Reversible Inhibitor of MAO-A (RIMA), primarily used as an antidepressant, not for urinary disorders. * **B. Citalopram:** This is a Selective Serotonin Reuptake Inhibitor (SSRI). While used for depression and anxiety, it lacks the significant noradrenergic activity required to affect the urethral sphincter effectively. * **C. Nefazodone:** This is a SARI (Serotonin Antagonist and Reuptake Inhibitor). It is primarily used for depression but is rarely used now due to risks of hepatotoxicity. **High-Yield Clinical Pearls for NEET-PG:** * **Duloxetine Indications:** Apart from SUI and Depression, it is a first-line agent for **Diabetic Neuropathy**, Fibromyalgia, and Chronic Musculoskeletal pain. * **Mechanism in SUI:** It acts on the **Onuf’s Nucleus** (Sacral cord). * **Side Effects:** Nausea is the most common side effect; it can also cause insomnia and dry mouth. * **Contraindication:** Avoid in patients with uncontrolled narrow-angle glaucoma and severe hepatic impairment.

Question 42: Which of the following drugs shows antiepileptic activity?

A. Felbamate
B. Gabapentin
C. Molindone
D. All of the above (Correct Answer)

Explanation: **Explanation:** The correct answer is **D. All of the above**. This question tests the classification and clinical utility of various drugs acting on the Central Nervous System (CNS). 1. **Felbamate (Option A):** This is a broad-spectrum **newer antiepileptic drug (AED)**. Its mechanism involves blocking NMDA receptors and modulating GABA-A receptors. While effective for refractory partial seizures and Lennox-Gastaut syndrome, its use is limited due to the risk of aplastic anemia and hepatic failure. 2. **Gabapentin (Option B):** This is a structural analogue of GABA. Despite its name, it does not act directly on GABA receptors; instead, it binds to the **$\alpha_2\delta$ subunit of voltage-gated calcium channels**, decreasing glutamate release. It is used for focal seizures and neuropathic pain. 3. **Molindone (Option C):** Traditionally classified as a **typical antipsychotic** (dihydroindolone class), Molindone is the "trick" element of this question. In pharmacological studies and specific clinical contexts, Molindone has demonstrated **anticonvulsant properties**, particularly against maximal electroshock (MES) seizures. While not a first-line AED, it possesses documented antiepileptic activity. **High-Yield Clinical Pearls for NEET-PG:** * **Lennox-Gastaut Syndrome (LGS):** Drugs of choice include **Rufinamide, Felbamate, Topiramate, and Lamotrigine**. * **Gabapentin/Pregabalin:** Primarily used today for **Post-herpetic neuralgia** and **Diabetic neuropathy** rather than epilepsy. * **Weight Profile:** Unlike most antipsychotics that cause weight gain, **Molindone** is unique for being weight-neutral or causing slight weight loss. * **Broad-spectrum AEDs:** Remember the mnemonic **"Val-To-La-Fe"** (Valproate, Topiramate, Lamotrigine, Felbamate) for drugs effective against multiple seizure types.

Question 43: What is the drug of choice in drug-induced parkinsonism?

A. Levodopa
B. Benzhexol (Correct Answer)
C. Amantidine
D. Carbidopa

Explanation: ### Explanation **Concept:** Drug-induced parkinsonism (DIP) is a common extrapyramidal side effect (EPS) caused by dopamine (D2) receptor antagonists, such as typical antipsychotics (e.g., Haloperidol) or antiemetics (e.g., Metoclopramide). These drugs block dopamine receptors in the striatum, leading to a relative **cholinergic overactivity**. **Why Benzhexol is Correct:** Benzhexol (Trihexyphenidyl) is a **centrally acting anticholinergic** drug. It works by restoring the balance between dopamine and acetylcholine in the basal ganglia. Since the dopamine receptors are already blocked by the offending drug, adding more dopamine (Levodopa) is ineffective; instead, the excess cholinergic activity must be antagonized. **Why Other Options are Incorrect:** * **Levodopa & Carbidopa:** These are the gold standard for idiopathic Parkinson’s disease. However, in DIP, dopamine receptors are physically blocked by the offending antipsychotic. Therefore, increasing dopamine levels will not overcome the blockade and may even worsen the underlying psychosis for which the patient is being treated. * **Amantadine:** While it has mild anticholinergic and dopamine-releasing properties and can be used as a second-line agent, centrally acting anticholinergics like Benzhexol or Benztropine remain the primary drugs of choice. **High-Yield Clinical Pearls for NEET-PG:** * **Drug of Choice for DIP:** Central anticholinergics (Benzhexol, Benztropine, Biperiden). * **Acute Dystonia:** Also treated with parenteral anticholinergics or promethazine. * **Akathisia:** The drug of choice is **Propranolol**. * **Tardive Dyskinesia:** Anticholinergics are **contraindicated** as they worsen the condition; treatment involves switching to atypical antipsychotics (Clozapine) or using VMAT-2 inhibitors (Valbenazine).

Question 44: What is the treatment of choice for myoclonic epilepsy in children?

A. Phenytoin
B. Phenobarbitone
C. Sodium valproate (Correct Answer)
D. Ethosuximide

Explanation: **Explanation:** **Sodium Valproate** is the drug of choice for myoclonic epilepsy because it is a broad-spectrum antiepileptic drug (AED) that effectively covers multiple seizure types. Its mechanism involves increasing GABA levels, inhibiting T-type calcium channels, and prolonging the inactivated state of voltage-gated sodium channels. In pediatric populations, it is preferred for myoclonic seizures (including Juvenile Myoclonic Epilepsy) due to its high efficacy in preventing the sudden, brief muscle jerks characteristic of this condition. **Analysis of Incorrect Options:** * **Phenytoin (Option A):** This is a narrow-spectrum AED primarily used for focal and generalized tonic-clonic seizures. Crucially, Phenytoin (along with Carbamazepine) can actually **exacerbate** or worsen myoclonic and absence seizures. * **Phenobarbitone (Option B):** While used for neonatal seizures and status epilepticus, it is not the first-line choice for myoclonic epilepsy due to significant side effects like sedation, cognitive impairment, and behavioral changes in children. * **Ethosuximide (Option D):** This is the drug of choice for **Absence seizures** only. It acts specifically on T-type calcium channels in the thalamus but lacks efficacy against myoclonic or tonic-clonic components. **High-Yield Clinical Pearls for NEET-PG:** * **Broad Spectrum King:** Valproate is the DOC for most generalized seizures (Myoclonic, Atonic, and Tonic-Clonic). * **Teratogenicity:** Valproate is associated with the highest risk of neural tube defects (Spina Bifida). * **Side Effects Mnemonic (VALPROATE):** **V**omiting, **A**lopecia, **L**iver toxicity (Hepatotoxicity), **P**ancreatitis, **R**etained fat (Weight gain), **O**edema, **A**norexia, **T**remors, **E**nzyme inhibitor. * **Alternative:** Levetiracetam is increasingly used as an alternative to Valproate in females of childbearing age to avoid teratogenicity.

Question 45: All of the following are adverse effects of sodium valproate EXCEPT?

A. Weight gain
B. Alopecia
C. Liver damage
D. Osteomalacia (Correct Answer)

Explanation: **Explanation:** The correct answer is **D. Osteomalacia**. **1. Why Osteomalacia is the correct answer:** Sodium valproate is unique among older-generation antiepileptics because it is a **potent enzyme inhibitor**, not an inducer. Osteomalacia (and osteoporosis) is typically associated with **enzyme-inducing** antiepileptics like Phenytoin, Phenobarbital, and Carbamazepine. These drugs induce Cytochrome P450 enzymes, which accelerate the metabolism of Vitamin D, leading to calcium deficiency and bone demineralization. Since Valproate inhibits enzymes, it does not typically cause this metabolic bone disease. **2. Analysis of Incorrect Options:** * **A. Weight gain:** This is a very common side effect of Valproate (unlike Topiramate or Zonisamide, which cause weight loss). It is often associated with increased appetite and insulin resistance. * **B. Alopecia:** Valproate frequently causes transient hair loss or thinning. When the hair regrows, it may have a different texture (curly/wavy hair). * **C. Liver damage:** Hepatotoxicity is a serious, idiosyncratic adverse effect of Valproate, especially in children under two years of age or those with mitochondrial disorders (POLG mutations). **3. High-Yield Clinical Pearls for NEET-PG:** * **Mnemonic for Valproate Side Effects (VALPROATE):** **V**omiting, **A**lopecia, **L**iver toxicity, **P**ancreatitis/PCOS, **R**etention of weight (gain), **O**edema, **A**norexia (rarely), **T**eratogenicity (Neural Tube Defects), **E**nzyme inhibitor. * **Teratogenicity:** Valproate has the highest risk of **Neural Tube Defects (Spina Bifida)** among all AEDs. * **Drug of Choice:** It is the drug of choice for **Generalized Tonic-Clonic Seizures (GTCS)**, Myoclonic seizures, and Absence seizures.

Question 46: What is the most common side effect of levodopa?

A. Diarrhoea
B. Nausea and vomiting (Correct Answer)
C. Tremor
D. Rash

Explanation: **Explanation:** **Nausea and vomiting** is the most common side effect of Levodopa, occurring in approximately 80% of patients when administered without a peripheral decarboxylase inhibitor. [2] **Mechanism:** Levodopa is a precursor to dopamine. When taken orally, a significant portion is converted into dopamine in the systemic circulation by the enzyme **DOPA decarboxylase**. [2] This peripheral dopamine stimulates the **Chemoreceptor Trigger Zone (CTZ)** located in the *area postrema* of the medulla. Since the CTZ lies outside the blood-brain barrier, it is easily accessible to circulating dopamine, triggering the emetic reflex. **Analysis of Incorrect Options:** * **A. Diarrhoea:** This is not a characteristic side effect of Levodopa. In fact, some antiparkinsonian drugs (like anticholinergics) are more likely to cause constipation. * **C. Tremor:** Levodopa is used to *treat* resting tremors in Parkinson’s disease. [1] While it can cause "dyskinesias" (abnormal involuntary movements) as a late-stage side effect, it does not typically cause tremors. [1] * **D. Rash:** While any drug can cause a hypersensitivity reaction, a rash is not a common or dose-limiting side effect of Levodopa. **High-Yield NEET-PG Pearls:** 1. **Carbidopa/Benserazide:** To minimize nausea, Levodopa is co-administered with peripheral decarboxylase inhibitors. [2] These do not cross the BBB, ensuring more Levodopa reaches the brain while reducing peripheral dopamine levels. 2. **Domperidone:** If vomiting persists, Domperidone is the preferred antiemetic because it is a peripheral dopamine antagonist that does not cross the BBB (unlike Metoclopramide, which would worsen Parkinsonian symptoms). 3. **The "On-Off" Phenomenon:** A high-yield clinical complication of long-term Levodopa therapy characterized by sudden fluctuations in motor performance. [3]

Question 47: Which of the following is a dopamine receptor agonist?

A. Methyldopa
B. Bromocriptine (Correct Answer)
C. Haloperidol
D. Morphine

Explanation: **Explanation:** **Bromocriptine** is the correct answer because it is a potent **D2 receptor agonist** [1], [2] and a partial D1 antagonist. Derived from ergot alkaloids, it directly stimulates dopamine receptors in the brain [1]. Clinically, it is used to treat conditions characterized by dopamine deficiency or prolactin excess, such as Parkinson’s disease, hyperprolactinemia (prolactinomas), and acromegaly [3]. **Analysis of Incorrect Options:** * **Methyldopa (A):** This is a centrally acting alpha-2 adrenergic agonist. It acts as a "false neurotransmitter" precursor and is primarily used as an antihypertensive, particularly in pregnancy-induced hypertension. * **Haloperidol (C):** This is a typical antipsychotic that acts as a **dopamine (D2) receptor antagonist**. It blocks dopamine pathways, which is the opposite action of Bromocriptine. * **Morphine (D):** This is a potent opioid analgesic that acts primarily as an agonist at **mu (μ) opioid receptors**. It does not act directly as a dopamine receptor agonist. **High-Yield Clinical Pearls for NEET-PG:** * **Non-Ergot Agonists:** Modern practice often prefers non-ergot dopamine agonists like **Pramipexole** and **Ropinirole** for Parkinson’s disease due to a lower risk of valvular heart disease and pulmonary fibrosis [1]. * **Cabergoline:** Another ergot derivative like Bromocriptine, but preferred for hyperprolactinemia due to its longer half-life (once or twice weekly dosing) and better tolerability [3]. * **Quick Recall:** Dopamine agonists are also used in the treatment of **Restless Leg Syndrome (RLS)** and **Neuroleptic Malignant Syndrome (NMS)**.

Question 48: Which of the following is a 5-HT2A antagonist drug?

A. Clozapine
B. Cisapride
C. Sumatriptan
D. Ketanserin (Correct Answer)

Explanation: **Explanation:** **Ketanserin** is a selective **5-HT2A receptor antagonist** that also possesses $\alpha_1$-adrenergic blocking properties. Its primary pharmacological action involves blocking 5-HT2A receptors on smooth muscles (causing vasodilation) and platelets (inhibiting aggregation). Clinically, it has been used as an antihypertensive agent and in the management of Raynaud’s phenomenon and carcinoid syndrome. **Analysis of Incorrect Options:** * **Clozapine (Option A):** While Clozapine is an atypical antipsychotic that has high affinity for 5-HT2A receptors, it is primarily classified as a **D2/5-HT2A antagonist**. However, in the context of pure pharmacological classification for competitive exams, Ketanserin is the "prototype" 5-HT2A antagonist. * **Cisapride (Option B):** This is a **5-HT4 agonist**. It was used as a prokinetic agent to increase lower esophageal sphincter tone and accelerate gastric emptying, though its use is now restricted due to the risk of QT prolongation (Torsades de Pointes). * **Sumatriptan (Option C):** This is a selective **5-HT1B/1D agonist**. It is the gold standard for the acute treatment of migraine, acting via vasoconstriction of cranial vessels and inhibition of neuropeptide release. **High-Yield Clinical Pearls for NEET-PG:** * **Ritanserin** is another specific 5-HT2A antagonist often mentioned alongside Ketanserin. * **Cyproheptadine** is a non-selective 5-HT2 antagonist (also blocks H1) used in **Serotonin Syndrome**. * **5-HT3 Antagonists** (e.g., Ondansetron) are the only 5-HT receptors that are **ionotropic** (ligand-gated ion channels); all others are G-protein coupled receptors (GPCRs).

Question 49: Tranylcypromine (MAO Inhibitor) should be avoided with which of the following drugs due to the risk of dangerous drug interaction?

A. Morphine
B. Amitriptyline (Correct Answer)
C. Alprazolam
D. Alprazolam

Explanation: **Explanation:** **1. Why Amitriptyline is the Correct Answer:** Tranylcypromine is a non-selective, irreversible **Monoamine Oxidase Inhibitor (MAOI)**. Amitriptyline is a **Tricyclic Antidepressant (TCA)**. Both drugs increase the synaptic concentration of monoamines (Norepinephrine and Serotonin). When used together, they can lead to a massive accumulation of these neurotransmitters, resulting in severe **Serotonin Syndrome** or a **Hypertensive Crisis**. Clinical features include hyperpyrexia, tremors, seizures, and cardiovascular collapse. Therefore, a "washout period" of at least 14 days is mandatory when switching between these classes. **2. Why the Other Options are Incorrect:** * **A. Morphine:** While MAOIs can interact with certain opioids (specifically Pethidine/Meperidine, which can cause life-threatening excitatory reactions), Morphine does not have a major direct serotonergic interaction with MAOIs. However, caution is still advised. * **C & D. Alprazolam:** This is a Benzodiazepine. Benzodiazepines do not significantly affect the monoamine reuptake or metabolism pathways targeted by MAOIs. They are often used safely alongside antidepressants to manage acute anxiety or insomnia, provided there is no respiratory depression. **3. High-Yield Clinical Pearls for NEET-PG:** * **Cheese Reaction:** MAOIs (especially non-selective ones like Tranylcypromine) interact with **Tyramine-rich foods** (aged cheese, red wine), leading to a hypertensive crisis due to the displacement of Norepinephrine. * **Pethidine Contraindication:** Never give Pethidine with MAOIs; it can cause malignant hyperthermia. * **Drug of Choice for Hypertensive Crisis:** Phentolamine (Alpha-blocker) is the preferred treatment for MAOI-induced hypertensive emergencies. * **Moclobemide:** A RIMA (Reversible Inhibitor of MAO-A) has a much lower risk of these interactions compared to Tranylcypromine.

Question 50: What are the characteristic features of opioid withdrawal?

A. Rhinorrhea and lacrimation (Correct Answer)
B. Seizures
C. Delirium tremors
D. Transient visual, tactile or auditory hallucinations

Explanation: **Explanation:** Opioid withdrawal is characterized by a state of **autonomic hyperactivity** and "rebound" CNS excitability. Since opioids typically cause miosis (constriction), constipation, and sedation, their withdrawal results in the opposite physiological effects. **1. Why Option A is Correct:** **Rhinorrhea and lacrimation** are classic early signs of opioid withdrawal. The sudden cessation of opioid receptor stimulation leads to excessive parasympathetic-like activity and increased secretions. Other hallmark features include **yawning, piloerection (gooseflesh)**, mydriasis (dilated pupils), diaphoresis, and intense abdominal cramping with diarrhea. **2. Why the Other Options are Incorrect:** * **Options B, C, and D (Seizures, Delirium Tremens, and Hallucinations):** These are characteristic of **Alcohol withdrawal** or **Sedative-Hypnotic (Benzodiazepine/Barbiturate) withdrawal**. * Unlike alcohol withdrawal, **uncomplicated opioid withdrawal is rarely life-threatening**, although it is extremely distressing ("the flu from hell"). * Seizures are notably absent in opioid withdrawal, with one major exception: withdrawal from **Meperidine (Pethidine)**, which can cause tremors and seizures due to the accumulation of its metabolite, normeperidine. **Clinical Pearls for NEET-PG:** * **Objective Sign:** **Piloerection** is the most objective sign of opioid withdrawal (origin of the term "cold turkey"). * **Pupillary changes:** Opioid overdose = Pinpoint pupils; Opioid withdrawal = Mydriasis. * **Management:** * **Clonidine** (α2 agonist) helps reduce autonomic symptoms (tachycardia, hypertension). * **Methadone or Buprenorphine** are used for detoxification and maintenance therapy. * **Naloxone:** Administration in an opioid-dependent patient will trigger **precipitated withdrawal**, which is more rapid and intense than spontaneous withdrawal.

Practice by Chapter

General Anesthetics

Practice Questions

Local Anesthetics

Practice Questions

Sedative-Hypnotics

Practice Questions

Antiepileptic Drugs

Practice Questions

Antiparkinsonian Drugs

Practice Questions

Opioid Analgesics

Practice Questions

Drugs of Abuse and Addiction

Practice Questions

Psychostimulants

Practice Questions

Hallucinogens

Practice Questions

CNS Stimulants and Cognitive Enhancers

Practice Questions

Want unlimited practice?

Get full access to all questions, explanations, and performance tracking.

Start For Free