Central Nervous System Pharmacology — MCQs

Central Nervous System Pharmacology Indian Medical PG Practice Questions and MCQs

Question 811: What is the drug of choice for treating restless leg syndrome in a woman who developed pain and crawling sensation on her legs at night?

A. Pramipexole (Correct Answer)
B. Gabapentin
C. Vitamin B12
D. Iron tablets

Explanation: ***Pramipexole*** - **Pramipexole** is a **dopamine agonist** (D2/D3 receptor agonist) that is highly effective in treating **restless leg syndrome (RLS)** and is FDA-approved for moderate-to-severe RLS. - It helps alleviate the characteristic **pain, crawling sensations (paresthesias)**, and the urge to move the legs, especially at night. - **First-line treatment** along with other dopamine agonists like ropinirole and rotigotine. - **Preferred in many guidelines** as a primary pharmacological option for RLS. *Gabapentin* - **Gabapentin** (and gabapentin enacarbil) is an **alpha-2-delta ligand** that is also considered a **first-line treatment option** for RLS per recent guidelines. - Particularly useful in patients with **comorbid insomnia, neuropathic pain**, or when there is concern about **augmentation** (worsening of symptoms with long-term dopamine agonist use). - While equally effective, **dopamine agonists like pramipexole** are more traditionally recognized as the primary choice in conventional teaching and previous exam questions. *Vitamin B12* - **Vitamin B12 deficiency** can cause **neurological symptoms** like numbness or tingling, but supplementation is **not a direct treatment for primary RLS** unless a specific deficiency is identified and contributing to symptoms. - No direct evidence supporting **Vitamin B12 supplementation** as a primary treatment for RLS itself. *Iron tablets* - **Iron deficiency** (ferritin <75 μg/L) is a common and important cause of **secondary RLS**, and **iron supplementation** should be considered when low iron stores are identified. - However, for primary RLS or without confirmed iron deficiency, iron tablets are **not the primary pharmacological treatment**, and dopamine agonists like pramipexole remain the preferred initial option.

Question 812: A female patient presents to you with a unilateral headache. It is associated with nausea, photophobia, and phonophobia. What is the drug of choice for acute management?

A. Flunarizine
B. Sumatriptan (Correct Answer)
C. Propranolol
D. Topiramate

Explanation: ***Sumatriptan*** - **Sumatriptan**, a **triptan**, is an effective abortive therapy for **acute migraine attacks** due to its selective serotonin 5-HT1B/1D receptor agonist action, leading to vasoconstriction and inhibition of neurogenic inflammation. - The symptoms described—**unilateral headache**, nausea, **photophobia**, and **phonophobia**—are classic features of migraine. *Flunarizine* - **Flunarizine** is a **calcium channel blocker** used for migraine **prophylaxis**, not for acute treatment. - It is typically prescribed for patients experiencing frequent or severe migraine attacks to reduce their incidence. *Propranolol* - **Propranolol** is a **beta-blocker** primarily used for migraine **prophylaxis**. - It helps prevent migraine attacks by modulating cerebral blood flow and neuronal excitability, but it is not effective for acute pain relief during an attack. *Topiramate* - **Topiramate** is an **antiepileptic drug** often used for migraine **prophylaxis**. - It works by various mechanisms, including altering neurotransmitter activity, but it does not provide acute symptomatic relief for an ongoing migraine attack.

Question 813: Which drug, used to lower intraocular pressure (IOP) in a patient with optic disc changes and ciliary congestion, acts by increasing uveoscleral outflow?

A. Pilocarpine
B. Timolol
C. Latanoprost (Correct Answer)
D. Dorzolamide

Explanation: ***Latanoprost*** - Latanoprost is a **prostaglandin analog** that primarily works by increasing the **uveoscleral outflow** of aqueous humor, effectively lowering intraocular pressure. - It is a first-line agent for glaucoma due to its efficacy and once-daily dosing. *Pilocarpine* - Pilocarpine is a **miotic agent** that increases aqueous humor outflow through the **trabecular meshwork** by causing ciliary muscle contraction, not uveoscleral outflow. - Its mechanism involves opening the trabecular spaces to facilitate drainage. *Timolol* - Timolol is a **beta-adrenergic blocker** that reduces intraocular pressure by **decreasing the production of aqueous humor**, not by increasing outflow. - It works by blocking beta-receptors in the ciliary body. *Dorzolamide* - Dorzolamide is a **carbonic anhydrase inhibitor** that lowers intraocular pressure by **reducing the secretion of aqueous humor** by the ciliary body. - It acts on the enzymes responsible for fluid production, not outflow pathways.

Question 814: A person was given a muscle relaxant that competitively blocks nicotinic receptors. Which of the following drugs is used for reversal of muscle relaxation after surgery?

A. Carbachol
B. Succinylcholine
C. Physostigmine
D. Neostigmine (Correct Answer)

Explanation: ***Neostigmine*** - **Neostigmine** is an **acetylcholinesterase inhibitor** that increases the amount of acetylcholine at the neuromuscular junction, thereby overcoming the competitive block at nicotinic receptors [1], [4]. - This increase in acetylcholine effectively reverses the paralysis caused by **nondepolarizing muscle relaxants**, making it useful for post-surgical recovery [2]. *Carbachol* - **Carbachol** is a **direct-acting cholinergic agonist** that stimulates both muscarinic and nicotinic receptors and is not typically used for reversing competitive neuromuscular blockade. - Its primary use is for glaucoma and to stimulate the bladder or bowels, not to counteract muscle relaxants. *Succinylcholine* - **Succinylcholine** is a **depolarizing muscle relaxant** and would prolong, rather than reverse, muscle blockade if administered after a competitive blocker [3]. - It works by initially causing depolarization and then preventing further muscle contraction, leading to paralysis. *Physostigmine* - **Physostigmine** is an **acetylcholinesterase inhibitor** that crosses the blood-brain barrier, making it more suitable for treating central anticholinergic toxicity rather than peripheral neuromuscular blockade. - While it inhibits acetylcholinesterase, its central effects and potential for seizures limit its use for reversing surgical muscle relaxation.

Question 815: Which of the following is the only clinically available depolarizing muscle relaxant?

A. Decamethonium
B. Suxamethonium (Correct Answer)
C. Mivacurium
D. None of the options

Explanation: ***Suxamethonium*** - **Suxamethonium** (also known as succinylcholine) is currently the **only depolarizing neuromuscular blocker** available for clinical use. - It works by mimicking acetylcholine, binding to and activating nicotinic acetylcholine receptors at the **neuromuscular junction**, causing initial muscle fasciculations followed by relaxation. *Decamethonium* - **Decamethonium** is a depolarizing neuromuscular blocker but is **no longer clinically available** due to its prolonged action and side effects. - It also acts by opening nicotinic acetylcholine receptor channels, leading to depolarization and muscle paralysis. *Mivacurium* - **Mivacurium** is a **nondepolarizing neuromuscular blocker**, meaning it acts as a competitive antagonist at the acetylcholine receptor. - It is known for its **short duration of action** due to rapid hydrolysis by plasma cholinesterases but is not depolarizing. *None of the options* - This option is incorrect because suxamethonium is indeed a clinically available depolarizing muscle relaxant. - The question specifically asks for the *only* clinically available one, which suxamethonium fulfills.

Question 816: What is the treatment for extrapyramidal side effects induced by Haloperidol?

A. Barbiturates
B. SSRIs
C. Benzodiazepines
D. Anticholinergic drugs (Correct Answer)

Explanation: ***Anticholinergic drugs (effective treatment)*** - **Anticholinergic medications**, such as **benztropine** or **diphenhydramine**, are the primary treatment for **acute extrapyramidal symptoms (EPS)** like dystonia and parkinsonism induced by antipsychotics like haloperidol. - They work by **blocking muscarinic acetylcholine receptors**, helping to restore the balance between dopamine and acetylcholine in the basal ganglia. *Benzodiazepines (used for anxiety and muscle relaxation)* - While benzodiazepines can offer some relief for **akathisia** (a form of EPS characterized by restlessness) due to their sedative and muscle relaxant properties, they are **not the first-line treatment for other acute EPS** such as dystonia or parkinsonism. - They primarily enhance **GABAergic transmission** and are effective for anxiety and seizure control rather than direct antagonism of EPS mechanisms. *Barbiturates (used as sedative-hypnotic drugs)* - **Barbiturates** are strong central nervous system depressants used for sedation, anesthesia, and seizure control, but are **not indicated for the treatment of EPS**. - Their significant **sedative and addictive potential**, along with a narrow therapeutic index, makes them unsuitable for this purpose. *SSRIs (used for depression and anxiety)* - **SSRIs (Selective Serotonin Reuptake Inhibitors)** are antidepressants that work by increasing serotonin levels in the brain and are used to treat depression, anxiety, and obsessive-compulsive disorder. - They **do not have a direct role** in ameliorating dopamine-acetylcholine imbalance responsible for haloperidol-induced EPS.

Question 817: Modafinil is primarily used for the treatment of which of the following conditions?

A. Narcolepsy (Correct Answer)
B. Sexual dysfunction
C. Depression
D. Anxiety

Explanation: ***Narcolepsy*** - **Modafinil** is a **eugeroic** (wakefulness-promoting agent) specifically approved and widely used for the treatment of excessive daytime sleepiness associated with **narcolepsy**. - Its mechanism involves increasing **dopamine** and **norepinephrine** levels, and modulating **orexin** pathways, promoting alertness without significant psychomotor stimulation. *Sexual dysfunction* - While sometimes explored off-label for certain types of sexual dysfunction, **modafinil** is not a primary or approved treatment for this condition. - Primary treatments for sexual dysfunction often involve specific medications like **PDE5 inhibitors** or hormone therapy, depending on the cause. *Depression* - **Modafinil** is not a primary antidepressant, although it can be used as an **adjunctive therapy** in some cases to combat residual fatigue or hypersomnia associated with depression. - Standard treatment for depression involves **selective serotonin reuptake inhibitors (SSRIs)**, **serotonin-norepinephrine reuptake inhibitors (SNRIs)**, or other classes of antidepressants. *Anxiety* - **Modafinil** is a stimulant-like drug and can sometimes **exacerbate anxiety** in susceptible individuals due to its catecholaminergic effects. - Primary treatments for anxiety disorders include **selective serotonin reuptake inhibitors (SSRIs)**, **benzodiazepines** (for acute relief), and psychotherapy.

Question 818: Carbapenem which has a tendency to cause maximum seizures?

A. Imipenem (Correct Answer)
B. Ertapenem
C. Doripenem
D. Meropenem

Explanation: ***Imipenem*** - **Imipenem** is associated with the highest risk of **seizures** among the carbapenems, particularly in patients with **renal impairment**, pre-existing **CNS disorders**, or high doses. - Its high affinity for **GABA-A receptors** in the central nervous system is thought to contribute to its proconvulsant effects. *Ertapenem* - While all carbapenems carry some risk of seizures, **ertapenem** has a **lower incidence** compared to imipenem. - It is often favored in patients without CNS infections or severe renal dysfunction due to its once-daily dosing. *Doripenem* - **Doripenem** also has a relatively **low risk of seizures** compared to imipenem. - It is generally well-tolerated, with side effects similar to other carbapenems but at a reduced frequency for CNS events. *Meropenem* - **Meropenem** is known to have a **lower seizure potential** than imipenem, making it a preferred choice for patients with a history of seizures or those with CNS infections. - Its **reduced affinity** for GABA-A receptors contributes to its better CNS tolerability.

Question 819: Which dopamine receptor blocker is commonly used for intractable Sydenham chorea?

A. Warfarin
B. Risperidone
C. Valproate
D. Haloperidol (Correct Answer)

Explanation: ***Haloperidol*** - Haloperidol is a **typical antipsychotic** and **dopamine D2 receptor blocker** commonly used for severe or intractable Sydenham chorea due to its efficacy in controlling **hyperkinetic movements**. - Its mechanism of action involves reducing dopaminergic overactivity in the **basal ganglia**, which is implicated in the pathogenesis of chorea. - While effective, it carries a risk of **extrapyramidal side effects** and requires monitoring. *Valproate* - Valproate is an **anticonvulsant** and **mood stabilizer** that IS actually used as a **first-line treatment** for Sydenham chorea, often preferred due to better tolerability compared to typical antipsychotics. - However, valproate is **not a dopamine receptor blocker** - it works through GABAergic mechanisms and sodium channel blockade. - The question specifically asks for a dopamine receptor blocker, making haloperidol the correct answer. *Warfarin* - Warfarin is an **anticoagulant** prescribed to prevent **thromboembolic events**, and has no role in the treatment of Sydenham chorea. - Its mechanism involves inhibiting **vitamin K-dependent clotting factors**, which is unrelated to neurological movement disorders. *Risperidone* - Risperidone is an **atypical antipsychotic** that blocks both **dopamine D2** and **serotonin 5-HT2A receptors**. While it can be effective for chorea, it is generally considered a **second-line agent**. - It may be used when typical antipsychotics are poorly tolerated, offering potentially lower risk of **extrapyramidal side effects** compared to haloperidol, though it still carries risks.

Question 820: What is the preferred medication for treating severe cases of rheumatic chorea that do not respond to standard treatments?

A. Diazepam
B. Probenecid
C. Valproate
D. Haloperidol (Correct Answer)

Explanation: **Haloperidol** - **Haloperidol**, a **dopamine receptor antagonist**, is a highly effective medication for severe rheumatic chorea that is refractory to standard treatments like carbamazepine or valproate. - Its mechanism of action involves blocking dopamine receptors in the brain, thereby reducing the **hyperkinetic movements** characteristic of chorea. *Valproate* - **Valproate** is a commonly used antiepileptic drug that can be effective for managing chorea, especially in milder cases. - However, it is generally considered a second-line agent for severe, refractory cases of **rheumatic chorea** compared to haloperidol. *Diazepam* - **Diazepam** is a benzodiazepine, primarily used for its **anxiolytic** and **sedative** properties due to its effect on GABA receptors. - While it can help alleviate some motor restlessness, it is not a first-line treatment for the involuntary movements of **chorea** and lacks the specific anti-chorea efficacy of antipsychotics. *Probenecid* - **Probenecid** is a uricosuric drug used to treat **gout** by increasing the excretion of uric acid. - It has no known role or efficacy in the management of **rheumatic chorea**.

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