Central Nervous System Pharmacology — MCQs

Central Nervous System Pharmacology Indian Medical PG Practice Questions and MCQs

Question 231: Sumatriptan is contraindicated in which of the following conditions?

A. Asthma
B. Diabetes Mellitus (DM)
C. Sepsis
D. Peripheral vascular disease (Correct Answer)

Explanation: ### Explanation **Mechanism of Action:** Sumatriptan is a selective **5-HT$_{1B/1D}$ receptor agonist**. Its therapeutic effect in migraine is mediated by two mechanisms: 1. **Vasoconstriction:** Stimulation of 5-HT$_{1B}$ receptors causes constriction of dilated intracranial extracerebral blood vessels. 2. **Neuronal Inhibition:** Stimulation of 5-HT$_{1D}$ receptors on trigeminal nerve terminals inhibits the release of pro-inflammatory neuropeptides (e.g., CGRP). **Why Peripheral Vascular Disease (PVD) is the Correct Answer:** The vasoconstrictive effect of triptans is not strictly limited to cranial vessels. They can cause systemic vasoconstriction, including coronary and peripheral arteries. In patients with **Peripheral Vascular Disease (PVD)**, ischemic heart disease (Prinzmetal angina, MI), or uncontrolled hypertension, triptans can exacerbate ischemia, potentially leading to gangrene or myocardial infarction. Thus, PVD is a **strict contraindication**. **Analysis of Incorrect Options:** * **A. Asthma:** Unlike non-selective beta-blockers or NSAIDs (which can trigger aspirin-exacerbated respiratory disease), triptans do not affect bronchial smooth muscle and are safe in asthmatics. * **B. Diabetes Mellitus:** DM is not a direct contraindication, though long-standing diabetics should be screened for underlying silent coronary artery disease before starting triptans. * **C. Sepsis:** While sepsis is a critical condition, it is not a specific contraindication for sumatriptan use in a patient who happens to have a migraine. **High-Yield Clinical Pearls for NEET-PG:** * **Drug of Choice:** Triptans are the DOC for **acute severe migraine** attacks but are *not* used for prophylaxis. * **Serotonin Syndrome:** Avoid combining triptans with MAO inhibitors or SSRIs/SNRIs due to the risk of Serotonin Syndrome. * **The "Triptan Sensation":** Patients may report chest tightness or paresthesia; while usually benign, it must be distinguished from true ischemia. * **Ergotamine:** Should not be used within 24 hours of a triptan due to additive vasospasm.

Question 232: Pseudolymphoma can result from long-term use of which medication?

A. Phenytoin (Correct Answer)
B. Carbamazepine
C. Sodium valproate
D. Phenobarbital

Explanation: **Explanation:** **Phenytoin** is a well-known cause of **Pseudolymphoma** (also known as Phenytoin-induced lymphadenopathy). This is a hypersensitivity reaction characterized by fever, skin rash, and generalized lymphadenopathy that clinically and histologically mimics Hodgkin’s or non-Hodgkin’s lymphoma. The condition is usually benign and reversible upon discontinuation of the drug, though in rare cases, it may progress to true malignant lymphoma. **Analysis of Options:** * **Phenytoin (Correct):** It induces a type IV hypersensitivity reaction. It is also associated with "DRESS syndrome" (Drug Reaction with Eosinophilia and Systemic Symptoms). * **Carbamazepine:** While it can cause skin rashes (Stevens-Johnson Syndrome) and blood dyscrasias (aplastic anemia), it is not classically associated with pseudolymphoma. * **Sodium Valproate:** Common side effects include weight gain, hepatotoxicity, alopecia, and pancreatitis, but not lymphadenopathy. * **Phenobarbital:** Primarily causes sedation, cognitive impairment, and osteomalacia; it does not typically cause pseudolymphoma. **High-Yield Clinical Pearls for NEET-PG:** * **Mnemonic for Phenytoin Side Effects (PH_E_NYTOIN):** **P**-P450 inducer, **H**-Hirsutism, **E**-Enlarged gums (Gingival hyperplasia), **N**-Nystagmus, **Y**-Yellow-brown skin (Pigmentation), **T**-Teratogenicity (Fetal Hydantoin Syndrome), **O**-Osteomalacia, **I**-Interference with B12/Folate (Megaloblastic anemia), **N**-Neuropathy & **N**-Nodes (Pseudolymphoma). * **Gingival Hyperplasia:** Caused by increased expression of Platelet-Derived Growth Factor (PDGF). * **Zero-order Kinetics:** Phenytoin follows saturation kinetics at therapeutic doses.

Question 233: Concomitant administration of clonazepam with which of the following antiepileptic drugs can precipitate absence status?

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

Explanation: **Explanation:** The correct answer is **Sodium Valproate**. **Mechanism of Interaction:** The precipitation of **absence status (non-convulsive status epilepticus)** is a well-documented, though rare, idiosyncratic drug interaction between **clonazepam** and **sodium valproate**. While both drugs are individually effective in treating absence seizures, their concomitant use can paradoxically trigger prolonged absence attacks. The exact pathophysiology is not fully understood, but it is hypothesized to involve complex alterations in GABAergic neurotransmission within the thalamocortical pathways, which are responsible for the 3-Hz spike-and-wave discharges characteristic of absence epilepsy. **Analysis of Incorrect Options:** * **Phenobarbitone:** This is a barbiturate that increases the duration of GABA-A channel opening. While it causes sedation when used with benzodiazepines, it does not specifically precipitate absence status. * **Carbamazepine & Phenytoin:** These are sodium channel blockers. They are generally **contraindicated** in absence seizures because they can aggravate them, but they do not have a specific "status-precipitating" interaction with clonazepam. **High-Yield Clinical Pearls for NEET-PG:** * **Drug of Choice (DOC):** Sodium Valproate is the DOC for generalized tonic-clonic seizures (GTCS) and myoclonic seizures. Ethosuximide is the DOC for pure absence seizures. * **Paradoxical Effect:** Always remember the "Valproate + Clonazepam = Absence Status" triad for pharmacology MCQs. * **Contraindication:** Avoid Carbamazepine, Phenytoin, and Vigabatrin in patients with absence or myoclonic seizures as they can worsen the condition. * **Valproate Side Effects:** Hepatotoxicity (highest risk <2 years old), Teratogenicity (Neural tube defects), and Weight gain.

Question 234: Which of the following antiepileptic agents does not act by Na+ channel modulation?

A. Vigabatrin (Correct Answer)
B. Phenytoin
C. Valproate
D. Lamotrigine

Explanation: **Explanation:** The mechanism of action of antiepileptic drugs (AEDs) is a high-yield topic for NEET-PG. To answer this, one must distinguish between drugs that stabilize membranes via ion channels and those that enhance inhibitory neurotransmission. **1. Why Vigabatrin is the Correct Answer:** Vigabatrin does **not** act on sodium channels. Its mechanism is the **irreversible inhibition of GABA transaminase (GABA-T)**, the enzyme responsible for the degradation of GABA. By blocking this enzyme, Vigabatrin increases the concentration of GABA (the primary inhibitory neurotransmitter) in the synaptic cleft. **2. Analysis of Incorrect Options (Na+ Channel Blockers):** * **Phenytoin:** A classic sodium channel blocker that shows use-dependent (voltage-dependent) blockade, prolonging the inactivated state of the channel. * **Valproate:** A broad-spectrum AED with multiple mechanisms, but its primary action includes the blockade of voltage-gated sodium channels and T-type calcium channels. * **Lamotrigine:** Primarily acts by blocking voltage-gated sodium channels, which subsequently inhibits the release of excitatory neurotransmitters like glutamate. **Clinical Pearls for NEET-PG:** * **Vigabatrin Side Effect:** Associated with **permanent bilateral concentric visual field defects** (requires regular perimetry). * **Drug of Choice:** Vigabatrin is the drug of choice for **Infantile Spasms** associated with **Tuberous Sclerosis**. * **Other GABA-acting drugs:** Tiagabine (GAT-1 inhibitor), Diazepam/Phenobarbitone (GABA-A receptor modulators). * **Mnemonic for Na+ blockers:** "The **L**ame **P**heny **V**alue **C**ard" (**L**amotrigine, **P**henytoin, **V**alproate, **C**arbamazepine).

Question 235: Which of the following drug classes, if combined with Rivastigmine, decreases its efficacy?

A. Selective serotonin reuptake inhibitors
B. Reversible inhibitor of MAO-A
C. Tricyclic antidepressants (Correct Answer)
D. Atypical antidepressants

Explanation: **Explanation:** **1. Why Tricyclic Antidepressants (TCAs) are the correct answer:** Rivastigmine is a **centrally acting reversible acetylcholinesterase inhibitor** used primarily in the treatment of Alzheimer’s disease and Parkinson’s dementia [1]. Its therapeutic goal is to increase synaptic levels of acetylcholine (ACh) to improve cognitive function. **Tricyclic Antidepressants (TCAs)**, such as Amitriptyline and Imipramine, possess significant **antimuscarinic (anticholinergic) properties**. When combined, TCAs directly antagonize the effects of Rivastigmine at the receptor level. This pharmacological antagonism neutralizes the pro-cholinergic benefits of Rivastigmine, thereby decreasing its clinical efficacy and potentially worsening cognitive decline. **2. Why other options are incorrect:** * **A. SSRIs (e.g., Fluoxetine):** These primarily affect serotonin reuptake. While they may have side effects, they lack significant anticholinergic activity and do not directly oppose the mechanism of Rivastigmine. * **B. RIMAs (e.g., Moclobemide):** These inhibit the MAO-A enzyme to increase norepinephrine and serotonin levels. They do not interfere with the cholinergic system. * **D. Atypical Antidepressants:** Drugs like Mirtazapine or Bupropion have distinct mechanisms (e.g., $̡_2$ antagonism or DA/NE reuptake inhibition) and generally lack the potent anticholinergic profile seen in TCAs [2]. **3. Clinical Pearls & High-Yield Facts for NEET-PG:** * **Rivastigmine Unique Feature:** It inhibits both **Acetylcholinesterase (AChE)** and **Butyrylcholinesterase (BuChE)**, which may provide additional benefits in certain dementias [1]. * **Drug-Drug Interactions:** Always avoid "Prescribing Paradoxes"—giving a cholinergic (Rivastigmine/Donepezil) alongside an anticholinergic (TCAs, First-generation antihistamines, or Oxybutynin). * **Side Effects:** The most common side effects of Rivastigmine are GI-related (nausea, vomiting) due to increased peripheral cholinergic activity. * **Route:** Rivastigmine is available as a **transdermal patch**, which helps reduce GI side effects compared to oral administration.

Question 236: Which of the following local anesthetics is useful for topical administration only?

A. Procaine
B. Bupivacaine
C. Etidocaine
D. Benzocaine (Correct Answer)

Explanation: **Explanation:** The correct answer is **Benzocaine**. Local anesthetics (LAs) are categorized based on their solubility and clinical utility. **Benzocaine** is a PABA derivative characterized by very low water solubility. Due to this property, it is absorbed too slowly to be effective or safe for injection (as it could cause local tissue irritation or remain at the site indefinitely). However, its poor solubility makes it ideal for **topical/surface anesthesia**, as it stays on the mucous membranes or skin for a prolonged duration without significant systemic absorption. **Analysis of Incorrect Options:** * **Procaine (Option A):** An ester-type LA with low lipid solubility and potency. It is primarily used for infiltration and spinal anesthesia but has **poor topical activity** because it does not penetrate mucous membranes effectively. * **Bupivacaine (Option B):** A potent, long-acting amide LA used extensively for infiltration, nerve blocks, and spinal/epidural anesthesia. It is not used as a standalone topical agent. * **Etidocaine (Option C):** A long-acting amide LA similar to lidocaine but with a more profound motor block. It is used for regional nerve blocks and infiltration, not exclusively for topical use. **High-Yield Clinical Pearls for NEET-PG:** * **Methemoglobinemia:** Benzocaine is a classic trigger for methemoglobinemia (treated with Methylene Blue). * **Classification:** LAs are divided into **Esters** (Procaine, Benzocaine, Tetracaine, Cocaine) and **Amides** (Lidocaine, Bupivacaine, Ropivacaine). *Mnemonic: Amides have two "i"s in their name.* * **Cocaine:** The only LA that is a naturally occurring alkaloid and possesses intrinsic vasoconstrictor properties. * **Lidocaine:** The most versatile LA, used for both topical and injectable routes, and also as a Class IB antiarrhythmic.

Question 237: Regarding opioid-induced seizures, which statement is correct?

A. They usually occur at therapeutic doses.
B. Children are more susceptible. (Correct Answer)
C. Seizures occur only with 0-opioid agonists.
D. Diazepam is the drug of choice in treatment.

Explanation: Opioids generally act as CNS depressants; however, they can induce seizures through the inhibition of GABAergic interneurons (disinhibition) or direct excitatory effects at high doses. **1. Why Option B is Correct:** Children exhibit a significantly lower seizure threshold compared to adults. Their developing central nervous system is more sensitive to the excitatory side effects of opioids. This susceptibility is particularly noted with drugs like **Meperidine (Pethidine)** and **Morphine**, making pediatric dosing and monitoring critical. **2. Why Other Options are Incorrect:** * **Option A:** Opioid-induced seizures are dose-dependent. They rarely occur at therapeutic levels and are typically a manifestation of **acute toxicity** or accumulation of metabolites [1]. * **Option C:** While mu-receptors are primarily involved, seizures are not exclusive to them. For example, **kappa-opioid agonists** and certain mixed agonist-antagonists can also trigger epileptiform activity. Furthermore, the metabolite **Normeperidine** (from Meperidine) is a potent non-opioid CNS stimulant that causes seizures. * **Option D:** While Diazepam is a general anticonvulsant, the definitive management for opioid toxicity is the competitive antagonist **Naloxone**. If seizures are specifically due to Normeperidine accumulation (common in renal failure), Naloxone may be less effective, but it remains the primary intervention for opioid-induced CNS effects [1]. **High-Yield Clinical Pearls for NEET-PG:** * **Meperidine (Pethidine):** Its metabolite, **Normeperidine**, has a long half-life and is the most common cause of opioid-induced seizures, especially in patients with **renal impairment**. * **Tramadol:** A very high-yield cause of seizures in clinical practice, even at near-therapeutic doses, due to its effect on serotonin and norepinephrine reuptake. * **Morphine:** Can cause "Stiff Man Syndrome" or myoclonus at high doses, which may precede generalized seizures.

Question 238: Which of the following calcium channel blockers is indicated for increased intracranial tension?

A. Nicardipine
B. Nimodipine (Correct Answer)
C. Clevidipine
D. Nitrendipine

Explanation: ### Explanation **Correct Option: B. Nimodipine** The correct answer is **Nimodipine** because of its unique pharmacological profile. While most Dihydropyridine (DHP) calcium channel blockers (CCBs) act primarily on peripheral vasculature, Nimodipine is highly **lipid-soluble**. This property allows it to readily cross the blood-brain barrier and exert a selective effect on cerebral blood vessels. In the context of increased intracranial tension (ICT) or subarachnoid hemorrhage (SAH), the primary concern is **cerebral vasospasm**, which leads to secondary ischemic neurological deficits. Nimodipine prevents and reverses this vasospasm, thereby improving cerebral perfusion and neurological outcomes. It is the gold-standard drug for preventing delayed cerebral ischemia in patients with SAH. **Analysis of Incorrect Options:** * **A. Nicardipine:** While it is used intravenously for hypertensive emergencies (including those with neurological involvement), it lacks the specific cerebrovascular selectivity and clinical evidence for vasospasm prophylaxis compared to Nimodipine. * **C. Clevidipine:** An ultra-short-acting IV DHP-CCB used for rapid blood pressure control in perioperative settings. It is metabolized by plasma esterases but is not indicated for cerebral vasospasm. * **D. Nitrendipine:** Primarily used for the management of systemic hypertension; it does not have a specific role in managing intracranial tension or cerebral vasospasm. **High-Yield Clinical Pearls for NEET-PG:** * **Drug of Choice (DOC):** Nimodipine is the DOC for preventing **Cerebral Vasospasm** following Subarachnoid Hemorrhage. * **Administration:** It should be started within 96 hours of SAH onset and continued for 21 days. * **Other CNS CCBs:** **Flunarizine** is another CCB that crosses the BBB, but it is used for **Migraine Prophylaxis**, not acute ICT. * **Nimodipine "Rule":** Remember "Nimo" for "Neuro"—it is the most neuro-specific calcium channel blocker.

Question 239: Baclofen acts as which of the following?

A. GABAA receptor agonist
B. GABAB receptor agonist (Correct Answer)
C. GABAA receptor antagonist
D. GABAB receptor antagonist

Explanation: **Explanation:** **Baclofen** is a centrally acting skeletal muscle relaxant primarily used to treat spasticity. Its mechanism of action is rooted in its role as a selective **GABA$_B$ receptor agonist**. 1. **Why Option B is Correct:** GABA$_B$ receptors are G-protein coupled receptors (metabotropic) located both pre-synaptically and post-synaptically in the spinal cord. Baclofen mimics the inhibitory effects of GABA at these sites. By activating these receptors, it increases potassium ($K^+$) conductance (hyperpolarization) and inhibits calcium ($Ca^{2+}$) influx. This results in the inhibition of both monosynaptic and polysynaptic reflexes in the spinal cord, leading to reduced muscle spasticity. 2. **Why Other Options are Incorrect:** * **Options A & C:** GABA$_A$ receptors are ionotropic (ligand-gated chloride channels). Drugs like Benzodiazepines and Barbiturates modulate GABA$_A$ receptors, not Baclofen. * **Option D:** A GABA$_B$ antagonist (e.g., Saclofen) would block inhibitory signals, potentially increasing neuronal excitability, which is the opposite of Baclofen’s therapeutic goal. **Clinical Pearls for NEET-PG:** * **Clinical Use:** It is the drug of choice for spasticity resulting from **Multiple Sclerosis** and spinal cord injuries. * **Route:** Can be administered orally or via an **intrathecal pump** for severe cases. * **Side Effects:** Drowsiness, fatigue, and muscle weakness. * **Withdrawal Warning:** Sudden discontinuation of Baclofen can lead to visual hallucinations, tachycardia, and seizures; it must be tapered gradually. * **Comparison:** Unlike Diazepam (which acts on GABA$_A$), Baclofen causes less sedation at therapeutic doses.

Question 240: Which non-synthetic alkaloid compound acts similarly to amphetamine?

A. Caffeine
B. Cocaine
C. Nicotine
D. All of the above (Correct Answer)

Explanation: **Explanation:** The correct answer is **D. All of the above**. The underlying medical concept is that **Amphetamine** is a potent CNS stimulant that acts as an indirect sympathomimetic by increasing the synaptic concentration of monoamines (Dopamine, Norepinephrine, and Serotonin). While amphetamine itself is a synthetic compound, several **non-synthetic alkaloids** (naturally occurring nitrogenous organic compounds) mimic its stimulatory effects through various mechanisms: * **Cocaine:** A natural alkaloid derived from *Erythroxylum coca*. Like amphetamine, it increases synaptic monoamines, specifically by **blocking the reuptake** of Dopamine, Norepinephrine, and Serotonin (DAT, NET, and SERT inhibitors). * **Caffeine:** A methylxanthine alkaloid found in coffee beans and tea leaves. It acts as an **adenosine receptor antagonist**. Since adenosine normally inhibits the release of excitatory neurotransmitters, caffeine results in increased CNS activity, mimicking the alertness produced by amphetamine. * **Nicotine:** A pyrrolidine alkaloid found in *Nicotiana tabacum*. It stimulates **nicotinic acetylcholine receptors (nAChRs)**, leading to the downstream release of dopamine and adrenaline, producing stimulant effects similar to low-dose amphetamines. **High-Yield Clinical Pearls for NEET-PG:** * **Mechanism Distinction:** Amphetamine *releases* stored catecholamines (via VMAT-2 and TAAR1), whereas Cocaine *blocks reuptake*. * **Ephedrine & Cathinone:** These are other important naturally occurring alkaloids (from *Ephedra* and *Khat*) that are structurally and functionally similar to amphetamine. * **Toxicity:** Overdose of any of these stimulants typically presents with a **Sympathomimetic Toxidrome** (tachycardia, hypertension, mydriasis, and diaphoresis). Note: Cocaine is unique as it also possesses local anesthetic properties (sodium channel blockade).

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