Central Nervous System Pharmacology — MCQs

Central Nervous System Pharmacology Indian Medical PG Practice Questions and MCQs

Question 571: Which of the following drugs should not be administered along with levodopa?

A. Carbidopa
B. MAO inhibitors
C. Vitamin B complex (Correct Answer)
D. Benserazide

Explanation: **Explanation:** The correct answer is **Vitamin B complex**, specifically due to the presence of **Pyridoxine (Vitamin B6)**. **1. Why Vitamin B complex is the correct answer:** Levodopa is a precursor to dopamine that must cross the blood-brain barrier (BBB) to be effective. In the periphery, the enzyme **aromatic L-amino acid decarboxylase (LAAD)** converts levodopa into dopamine. Pyridoxine acts as a vital cofactor for this enzyme. When Vitamin B6 is administered, it significantly accelerates the peripheral decarboxylation of levodopa. Since dopamine cannot cross the BBB, this leads to decreased availability of levodopa for the brain and increased peripheral side effects (like nausea and cardiac arrhythmias). **2. Why the other options are incorrect:** * **Carbidopa (A) and Benserazide (D):** These are **peripheral decarboxylase inhibitors**. They are intentionally co-administered with levodopa to prevent its peripheral breakdown, thereby increasing its CNS bioavailability and reducing side effects. * **MAO inhibitors (B):** While non-selective MAO inhibitors are contraindicated with levodopa (due to the risk of hypertensive crisis), selective **MAO-B inhibitors** (like Selegiline) are frequently used as adjuncts to levodopa therapy to prevent dopamine breakdown in the brain. **High-Yield Clinical Pearls for NEET-PG:** * **The "Pyridoxine Reversal":** This interaction only occurs when levodopa is given **alone**. If levodopa is combined with carbidopa (e.g., Sinemet), pyridoxine does *not* interfere with its action because the decarboxylase inhibitor blocks the peripheral effect of B6. * **Dietary Note:** Patients on levodopa monotherapy should be advised to avoid high-protein meals, as neutral amino acids compete with levodopa for transport across the BBB. * **Drug of Choice:** Levodopa + Carbidopa remains the gold standard for symptomatic management of Parkinson’s disease.

Question 572: A person has been consuming large quantities of alcohol daily for 20 years and is physically dependent on alcohol. Which drug should not be given to this person?

A. Disulfiram (Correct Answer)
B. Acamprosate
C. Naltrexone
D. Chlordiazepoxide

Explanation: **Explanation:** The core clinical issue in this scenario is the patient’s **physical dependence** on alcohol. In a chronic, heavy drinker, sudden cessation or the immediate administration of certain drugs can trigger life-threatening withdrawal or severe adverse reactions. **Why Disulfiram is the correct answer:** Disulfiram is an **aldehyde dehydrogenase inhibitor**. It works by causing the accumulation of acetaldehyde if alcohol is consumed. In a person who is physically dependent and likely has alcohol currently in their system, Disulfiram will trigger a **Disulfiram-Ethanol Reaction (DER)**. This manifests as severe flushing, tachycardia, hypotension, nausea, and potentially cardiovascular collapse. It is strictly contraindicated in patients who are currently intoxicated or have not abstained from alcohol for at least 12 hours. **Analysis of Incorrect Options:** * **Acamprosate:** An NMDA receptor antagonist used for maintaining abstinence. It does not cause a reaction with alcohol and is safe to start once withdrawal is managed. * **Naltrexone:** An opioid antagonist that reduces alcohol cravings by blocking the reward pathway. It can be started even while the patient is still drinking. * **Chlordiazepoxide:** A long-acting benzodiazepine. This is actually the **drug of choice** for managing acute alcohol withdrawal symptoms to prevent seizures and delirium tremens. **NEET-PG High-Yield Pearls:** * **Disulfiram Mechanism:** Irreversible inhibition of Aldehyde Dehydrogenase. * **Acamprosate:** Best for maintaining abstinence; excreted renally (avoid in renal failure). * **Naltrexone:** Best for reducing "heavy drinking" days; hepatotoxic (monitor LFTs). * **Wernicke’s Encephalopathy:** Always give Thiamine *before* Glucose in chronic alcoholics to prevent precipitating acute neurological decline.

Question 573: Which of the following statements is true for pramipexole?

A. Acts on dopamine receptors
B. First-line treatment for parkinsonism
C. Is not an ergot alkaloid
D. All of the above (Correct Answer)

Explanation: **Explanation:** Pramipexole is a **non-ergot dopamine agonist** that plays a significant role in the management of Parkinson’s disease. 1. **Mechanism of Action (Option A):** Pramipexole acts directly on postsynaptic dopamine receptors, specifically showing high affinity for the **D3 receptor subtype** (and some D2 activity). Unlike Levodopa, it does not require enzymatic conversion to be active. 2. **Clinical Utility (Option B):** It is considered a **first-line treatment** for Parkinson’s disease, particularly in younger patients (under 65 years). Initiating therapy with dopamine agonists helps delay the introduction of Levodopa, thereby postponing the onset of "on-off" fluctuations and dyskinesias. 3. **Chemical Class (Option C):** It is a **non-ergot derivative**. This is clinically significant because, unlike older ergot-derived agonists (like Bromocriptine or Pergolide), pramipexole does **not** cause retroperitoneal, pulmonary, or cardiac valvular fibrosis. **High-Yield NEET-PG Pearls:** * **Restless Leg Syndrome (RLS):** Pramipexole and Ropinirole are the drugs of choice for RLS. * **Neuroprotection:** It is thought to have antioxidant properties that may protect dopaminergic neurons. * **Side Effects:** Common side effects include nausea, hallucinations, and **impulse control disorders** (pathological gambling, hypersexuality) due to D3 stimulation in the mesolimbic pathway. * **Sudden Sleep Attacks:** Patients should be warned about the risk of falling asleep suddenly during daytime activities. * **Excretion:** Unlike Ropinirole (metabolized by CYP1A2), Pramipexole is excreted largely unchanged in the **urine**; thus, dose adjustment is required in renal failure.

Question 574: All are indications of lithium except?

A. Neutropenia
B. Major Depression
C. Vasculogenic Headaches
D. Generalized anxiety disorder (Correct Answer)

Explanation: **Explanation:** Lithium is the gold standard mood stabilizer primarily used for Bipolar Affective Disorder (BPAD) [1]. **Generalized Anxiety Disorder (GAD)** is the correct answer because Lithium has no established role in its management. GAD is typically treated with SSRIs, SNRIs, or Benzodiazepines (for short-term relief). **Analysis of Options:** * **Neutropenia:** Lithium induces **leukocytosis** (specifically neutrophilia) by stimulating the production of colony-stimulating factors in the bone marrow. This "side effect" is therapeutically utilized to treat iatrogenic neutropenia (e.g., post-chemotherapy or Clozapine-induced). * **Major Depression:** While not a first-line monotherapy, Lithium is a well-established **augmentation strategy** for treatment-resistant Major Depressive Disorder (MDD) [3]. It is also the only drug proven to reduce the risk of suicide in patients with mood disorders. * **Vasculogenic Headaches:** Lithium is a first-line agent for the prophylaxis of **Cluster Headaches** (a type of trigeminal autonomic cephalalgia/vasculogenic headache). **High-Yield Clinical Pearls for NEET-PG:** * **Mechanism:** Inhibits Inositol Monophosphatase (IP3/DAG pathway) and Glycogen Synthase Kinase-3 (GSK-3). * **Therapeutic Window:** Narrow (0.6–1.2 mEq/L). Toxicity starts >1.5 mEq/L. * **Side Effects (LITHIUM mnemonic):** **L**eukocytosis, **I**nsipidus (Nephrogenic Diabetes Insipidus), **T**remors/Teratogenicity (Ebstein’s Anomaly) [2], **H**ypothyroidism [2], **I**ncreased **U**rine, **M**others (avoid in pregnancy) [2]. * **Drug Interactions:** Thiazides, NSAIDs, and ACE inhibitors increase Lithium levels by decreasing its renal clearance.

Question 575: For which of the following seizures would carbamazepine, phenytoin, and primidone be prescribed as the appropriate drug treatment for prevention?

A. Complex partial seizures
B. Simple partial seizures
C. Status epilepticus
D. Generalized tonic-clonic seizures (Correct Answer)

Explanation: **Explanation:** The drugs mentioned—**Carbamazepine, Phenytoin, and Primidone**—are classic first-line or traditional anti-epileptic drugs (AEDs) primarily indicated for **Generalized Tonic-Clonic Seizures (GTCS)** and focal seizures. **1. Why Option D is Correct:** The primary mechanism of action for Phenytoin and Carbamazepine is the **blockade of voltage-gated sodium channels** in their inactivated state. This prevents high-frequency repetitive firing of neurons, which is the hallmark of GTCS. Primidone is metabolized into Phenobarbital and Phenylethylmalonamide (PEMA), both of which enhance GABAergic inhibition and are highly effective in controlling the motor manifestations of GTCS. **2. Analysis of Incorrect Options:** * **Options A & B (Partial Seizures):** While these drugs *are* effective for simple and complex partial (focal) seizures, the question asks for the specific group where all three are standard preventative treatments. In modern practice, Levetiracetam or Lamotrigine are often preferred for focal seizures due to better side-effect profiles. * **Option C (Status Epilepticus):** Status epilepticus is a medical emergency requiring **intravenous** medications for immediate termination. While IV Phenytoin (or Fosphenytoin) is used for maintenance, Carbamazepine and Primidone are not used in the acute management of status epilepticus because they lack rapid-acting IV formulations and Carbamazepine can actually worsen certain acute seizure types. **3. NEET-PG High-Yield Pearls:** * **Drug of Choice (DOC):** For GTCS, the DOC is **Valproate** (except in women of childbearing age, where Levetiracetam/Lamotrigine is preferred). * **Contraindication:** Carbamazepine and Phenytoin can **exacerbate Absence seizures and Myoclonic seizures**. * **Side Effects:** * **Phenytoin:** Gingival hyperplasia, hirsutism, and osteomalacia. * **Carbamazepine:** SIADH (hyponatremia) and Stevens-Johnson Syndrome (associated with HLA-B*1502). * **Enzyme Induction:** All three drugs are potent **Cytochrome P450 inducers**, leading to numerous drug-drug interactions (e.g., decreasing the efficacy of oral contraceptives).

Question 576: All of the following are anticonvulsants except?

A. Lamotrigine
B. Methylphenidate (Correct Answer)
C. Vigabatrin
D. Topiramate

Explanation: **Explanation:** The correct answer is **Methylphenidate** because it is a CNS stimulant, not an anticonvulsant. **1. Why Methylphenidate is the correct answer:** Methylphenidate acts primarily by increasing the synaptic concentration of dopamine and norepinephrine through the inhibition of their reuptake transporters (DAT and NET). It is the first-line pharmacological treatment for **Attention Deficit Hyperactivity Disorder (ADHD)** and is also used in Narcolepsy. Unlike anticonvulsants, which stabilize neuronal membranes to prevent seizures, stimulants can actually lower the seizure threshold in some patients. **2. Why the other options are incorrect (Anticonvulsants):** * **Lamotrigine:** A broad-spectrum anticonvulsant that blocks voltage-gated sodium channels and inhibits glutamate release. It is a drug of choice for Absence seizures and Bipolar disorder. * **Vigabatrin:** An irreversible inhibitor of **GABA transaminase**, the enzyme responsible for GABA degradation. This increases GABA levels in the brain. Its clinical use is limited due to the risk of permanent visual field defects. * **Topiramate:** A multi-mechanistic drug that blocks sodium channels, enhances GABA-A activity, and antagonizes AMPA/Kainate receptors. It is used for refractory seizures and migraine prophylaxis. **Clinical Pearls for NEET-PG:** * **Vigabatrin** is the drug of choice for **Infantile Spasms** associated with Tuberous Sclerosis. * **Lamotrigine** is notorious for causing **Stevens-Johnson Syndrome (SJS)**; hence, it requires slow dose titration. * **Topiramate** side effects include weight loss, nephrolithiasis (kidney stones), and "word-finding" difficulties. * **Methylphenidate** side effects include insomnia, appetite suppression, and growth retardation in children.

Question 577: Flumazenil antagonizes the effect of which drug?

A. Ketamine
B. Fentanyl
C. Midazolam (Correct Answer)
D. Propofol

Explanation: **Explanation:** **Correct Answer: C. Midazolam** Flumazenil is a specific **competitive antagonist** at the benzodiazepine (BZD) binding site on the **GABA-A receptor**. Midazolam is a short-acting benzodiazepine that works by increasing the frequency of chloride channel opening. Flumazenil rapidly reverses the sedative, psychomotor, and anticonvulsant effects of benzodiazepines, making it the drug of choice for BZD overdose and reversal of conscious sedation. **Why other options are incorrect:** * **A. Ketamine:** This is a dissociative anesthetic that acts primarily as an **NMDA receptor antagonist**. It is not affected by Flumazenil. * **B. Fentanyl:** This is a potent opioid analgesic acting on **mu (μ) opioid receptors**. Its specific antagonist is **Naloxone**. * **C. Propofol:** This intravenous anesthetic acts by enhancing GABA-A currents (at a site distinct from BZDs) and blocking sodium channels. There is no specific pharmacological antagonist for Propofol; recovery depends on redistribution and metabolism. **High-Yield Clinical Pearls for NEET-PG:** * **Half-life Caution:** Flumazenil has a very short half-life (~1 hour). Since many benzodiazepines (like Diazepam) have longer half-lives, **re-sedation** can occur, requiring repeated doses or an infusion. * **Seizure Risk:** Use Flumazenil with extreme caution in patients with chronic BZD use or tricyclic antidepressant (TCA) overdose, as it can precipitate **acute withdrawal seizures**. * **Specific Antagonists Memory Aid:** * Benzodiazepines $\rightarrow$ Flumazenil * Opioids $\rightarrow$ Naloxone * Heparin $\rightarrow$ Protamine Sulfate * Iron $\rightarrow$ Desferrioxamine

Question 578: What is the drug of choice for an acute attack of migraine?

A. Methysergide
B. Caffeine
C. Amitriptyline
D. Sumatriptan (Correct Answer)

Explanation: **Explanation:** **Sumatriptan** is the drug of choice for the management of an **acute attack of migraine** (moderate to severe). It belongs to the 'Triptan' class, which acts as selective **5-HT$_{1B/1D}$ receptor agonists**. Their therapeutic effect is mediated via three mechanisms: 1. **Vasoconstriction:** Stimulation of 5-HT$_{1B}$ receptors causes constriction of dilated cranial blood vessels. 2. **Neuropeptide Inhibition:** Stimulation of 5-HT$_{1D}$ receptors on trigeminal nerve terminals inhibits the release of pro-inflammatory neuropeptides (e.g., CGRP, Substance P). 3. **Central Inhibition:** Reduction of pain transmission in the trigeminal nucleus caudalis. **Analysis of Incorrect Options:** * **A. Methysergide:** A 5-HT antagonist used historically for **prophylaxis**, not acute attacks. It is now rarely used due to the risk of **retroperitoneal fibrosis**. * **B. Caffeine:** Often used as an adjuvant in combination with ergotamine or paracetamol to enhance absorption and provide mild vasoconstriction, but it is not the primary drug of choice. * **C. Amitriptyline:** A Tricyclic Antidepressant (TCA) which is the **drug of choice for migraine prophylaxis**, but it has no role in treating an ongoing acute attack. **High-Yield Clinical Pearls for NEET-PG:** * **Triptan Side Effects:** "Chest tightness" or "Triptan sensations" (due to coronary vasospasm). * **Contraindications:** Triptans are contraindicated in patients with Ischemic Heart Disease (IHD), Prinzmetal angina, and uncontrolled hypertension. * **Drug of Choice for Prophylaxis:** Amitriptyline (most common) or Propranolol. * **Drug of Choice for Migraine in Pregnancy:** Paracetamol (first-line); Sumatriptan is considered the safest triptan if needed.

Question 579: Lithium is used in the prophylactic treatment of which of the following conditions?

A. Schizophrenia
B. Manic Depressive Disorder (MDP) (Correct Answer)
C. Acute depression
D. Conversion reaction

Explanation: **Lithium** is the gold standard and first-line agent for the **prophylactic treatment of Manic Depressive Disorder (MDP)**, also known as Bipolar Disorder [1]. Its primary mechanism involves the inhibition of **Inositol Monophosphatase (IMPase)**, which depletes intracellular phosphoinositides (PIP2), thereby dampening overactive G-protein coupled signaling pathways (the "Inositol Depletion Hypothesis"). It is uniquely effective in preventing both manic and depressive relapses [1] and is the only drug proven to reduce the risk of suicide in these patients. **Analysis of Options:** * **A. Schizophrenia:** The primary treatment involves antipsychotics (D2 blockers). Lithium is not a standard treatment for schizophrenia unless there is a significant affective (mood) component [1]. * **C. Acute Depression:** While Lithium can augment antidepressants, it is not the first-line treatment for acute unipolar depression. Selective Serotonin Reuptake Inhibitors (SSRIs) are preferred. * **D. Conversion Reaction:** This is a somatoform disorder treated primarily with psychotherapy and counseling, not mood stabilizers. **High-Yield Clinical Pearls for NEET-PG:** * **Therapeutic Index:** Lithium has a very narrow therapeutic index. Monitoring serum levels is mandatory (Therapeutic range: **0.5–0.8 mEq/L** for prophylaxis; **0.8–1.2 mEq/L** for acute mania). * **Side Effects:** Common side effects include fine tremors, polyuria (Nephrogenic Diabetes Insipidus), and hypothyroidism. * **Teratogenicity:** Use in pregnancy is associated with **Ebstein’s Anomaly** (tricuspid valve malformation). * **Drug Interactions:** Thiazides, NSAIDs, and ACE inhibitors can increase lithium levels, leading to toxicity.

Question 580: A 4-month pregnant lady on regular treatment with valproate asks for advice regarding continuing the drug during pregnancy. What is the best course of action?

A. Immediately stop valproate and start lamotrigine
B. Change to carbamazepine
C. Continue valproate and monitor blood levels (Correct Answer)
D. Slowly taper the dose of valproate

Explanation: **Explanation:** The management of epilepsy during pregnancy is governed by a critical principle: **Never change or stop an effective anti-epileptic drug (AED) once pregnancy is confirmed.** **1. Why Option C is Correct:** By the time a woman realizes she is 4 months pregnant (second trimester), the period of organogenesis (weeks 3–8) is already complete. Valproate is associated with **Neural Tube Defects (NTDs)**, but these occur very early in the first trimester. Switching drugs now will not reverse any potential malformations but will expose the fetus to a new drug and risk breakthrough seizures in the mother. Seizures during pregnancy can cause fetal hypoxia, placental abruption, and miscarriage. Therefore, the safest approach is to continue the current effective dose and monitor serum levels, as physiological changes in pregnancy can alter drug pharmacokinetics. **2. Why Incorrect Options are Wrong:** * **Option A & B:** Switching to Lamotrigine or Carbamazepine at 4 months is futile for preventing teratogenicity. Furthermore, polytherapy or rapid switching increases the risk of "status epilepticus," which is more dangerous to the fetus than the drug itself. * **Option D:** Tapering the dose risks loss of seizure control. The goal is to maintain the lowest effective dose that was controlling seizures prior to pregnancy. **High-Yield Clinical Pearls for NEET-PG:** * **Pre-conception:** If a patient is planning pregnancy, Valproate should be avoided and switched to safer alternatives like **Lamotrigine or Levetiracetam**. * **Folic Acid:** High-dose folic acid (5 mg/day) should be started *before* conception to reduce NTD risk. * **Valproate Syndrome:** Characterized by spina bifida, craniofacial anomalies, and cognitive impairment. * **Vitamin K:** If the mother is on enzyme-inducing AEDs (e.g., Phenytoin, Carbamazepine), Vitamin K is given to the neonate to prevent hemorrhagic disease.

Practice by Chapter

General Anesthetics

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Local Anesthetics

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Sedative-Hypnotics

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Antiepileptic Drugs

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Antiparkinsonian Drugs

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Opioid Analgesics

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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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