Central Nervous System Pharmacology — MCQs

Central Nervous System Pharmacology Indian Medical PG Practice Questions and MCQs

Question 761: Which drug class is commonly used as a first-line treatment for neuropathic pain?

A. Antiepileptics (Correct Answer)
B. Tricyclic antidepressants (TCAs)
C. Opioids (narcotics)
D. Corticosteroids (anti-inflammatory drugs)

Explanation: ***Antiepileptics*** - Certain antiepileptics, particularly **gabapentin** and **pregabalin**, are considered **first-line agents** for neuropathic pain due to their ability to modulate **neurotransmitter release** in the central nervous system. - They work by binding to the **α2δ subunit of voltage-gated calcium channels**, reducing neuronal excitability. - These are often **preferred first-line** due to better tolerability compared to other first-line options. *Tricyclic antidepressants (TCAs)* - TCAs like **amitriptyline** and **nortriptyline** are also considered **first-line agents** for neuropathic pain by major guidelines. - However, they are often **less preferred** as initial therapy due to their significant **side effect profile**, such as **anticholinergic effects** and **cardiac toxicity**, especially in elderly patients. - Their mechanism involves **blocking the reuptake of norepinephrine and serotonin**, which modulates descending pain pathways. *Opioids (narcotics)* - **Opioids** are generally reserved for **severe neuropathic pain** that is refractory to first-line agents, due to concerns about **addiction**, **tolerance**, and a broad range of **side effects**. - They exert their analgesic effects by binding to **opioid receptors** in the central and peripheral nervous systems. *Corticosteroids (anti-inflammatory drugs)* - **Corticosteroids** are primarily used for **inflammatory pain** conditions and are generally **ineffective** for the direct treatment of neuropathic pain, which arises from nerve damage or dysfunction. - Their mechanism involves widespread **anti-inflammatory** and **immunosuppressive** effects.

Question 762: What is the drug of choice for the prophylactic treatment of migraine headaches?

A. Topiramate (Correct Answer)
B. Sumatriptan
C. Ibuprofen
D. Paracetamol

Explanation: ***Topiramate*** - **Topiramate** is a commonly prescribed and highly effective **antiepileptic drug** that is also approved for the prophylactic treatment of **migraine headaches**. - Its mechanism of action in migraine prevention involves **modulating neurotransmitter activity**, stabilizing neuronal excitability, and potentially reducing cortical spreading depression. *Sumatriptan* - **Sumatriptan** is a **triptan derivative** primarily used for the **acute treatment** of migraine attacks, not for prophylaxis. - It works by **constricting cranial blood vessels** and inhibiting the release of pro-inflammatory neuropeptides to abort an ongoing migraine. *Ibuprofen* - **Ibuprofen** is a **nonsteroidal anti-inflammatory drug (NSAID)** used for the **acute symptomatic relief** of mild to moderate headache pain, including some migraines. - It is not considered a primary drug for the **prophylactic prevention** of chronic migraine headaches. *Paracetamol* - **Paracetamol (acetaminophen)** is an **analgesic and antipyretic** used for general pain relief and fever, and can provide symptomatic relief for mild headaches. - Like ibuprofen, it does not have efficacy as a **prophylactic agent** for migraine prevention, nor is it recommended for this purpose.

Question 763: Which drug class is known for treating Parkinson's disease by inhibiting monoamine oxidase type B (MAO-B)?

A. Dopamine agonists
B. COMT inhibitors
C. MAO-B inhibitors (Correct Answer)
D. Anticholinergics

Explanation: ***MAO-B inhibitors*** - This drug class, which includes **selegiline** and **rasagiline**, specifically targets and inhibits **monoamine oxidase type B (MAO-B)**. - By inhibiting MAO-B, these drugs reduce the breakdown of **dopamine** in the brain, thereby increasing its availability and alleviating Parkinson's symptoms. *Dopamine agonists* - These drugs, such as **pramipexole** and **ropinirole**, directly stimulate **dopamine receptors** in the brain. - While effective in treating Parkinson's, their mechanism of action is **receptor activation**, not enzyme inhibition. *COMT inhibitors* - These drugs, like **entacapone** and **tolcapone**, inhibit **catechol-O-methyltransferase (COMT)**, an enzyme that metabolizes dopamine. - They are used as adjunct therapy to **levodopa** to prolong its effects, but they do not inhibit MAO-B. *Anticholinergics* - This class of drugs, including **benztropine** and **trihexyphenidyl**, targets the **cholinergic system** by blocking acetylcholine receptors. - They are primarily used to manage **tremor** and **dystonia** in Parkinson's disease, but their action is not on dopamine metabolism via MAO-B.

Question 764: A patient presents with severe headaches and is diagnosed with a migraine. Which drug, acting as a serotonin 1D agonist, is used to abort the migraine attack?

A. Dopamine 1 agonist
B. GABAB antagonist
C. Serotonin 1D agonist (Correct Answer)
D. Non-selective beta antagonist

Explanation: ***Serotonin 1D agonist*** - **Triptans**, a class of drugs acting as **5-HT1D/1B receptor agonists**, are the most specific and effective agents for aborting acute migraine attacks. - They work by causing **vasoconstriction of intracranial blood vessels** and inhibiting the release of **pro-inflammatory neuropeptides**. *Dopamine 1 agonist* - **Dopamine agonists** are generally used in conditions like **Parkinson's disease** to improve motor symptoms. - They are not indicated for the acute treatment of migraine as they do not target the specific pathways involved in migraine pathophysiology. *GABAB antagonist* - **GABA-B antagonists** are not used to abort migraine attacks; in fact, **GABA-B agonists** can sometimes be used to manage certain neurological conditions. - These drugs mainly modulate neuronal excitability and have no direct role in the acute vasoconstriction or pain pathways of migraine. *Non-selective beta antagonist* - **Non-selective beta-blockers** (e.g., propranolol) are primarily used for **migraine prophylaxis** (prevention), not for aborting an acute attack. - They work by reducing neuronal excitability and preventing the cascade of events that lead to a migraine, but they do not provide rapid relief during an attack.

Question 765: A 60-year-old man with Alzheimer's disease has been started on donepezil. What is the primary mechanism of action of this medication?

A. NMDA receptor antagonist
B. Acetylcholinesterase inhibitor (Correct Answer)
C. Dopamine receptor antagonist
D. Serotonin reuptake inhibitor

Explanation: ***Acetylcholinesterase inhibitor*** - Donepezil **blocks the enzyme acetylcholinesterase**, which is responsible for breaking down acetylcholine [1], [2]. - By inhibiting this enzyme, donepezil **increases the levels of acetylcholine** in the brain, improving **cholinergic neurotransmission** in patients with Alzheimer's disease [2]. *NMDA receptor antagonist* - **NMDA receptor antagonists** like **memantine** work by blocking the activity of glutamate at the NMDA receptor, which is thought to reduce excitotoxicity in Alzheimer's [1], [3]. - This mechanism is different from donepezil, which targets the **cholinergic system** [1]. *Dopamine receptor antagonist* - **Dopamine receptor antagonists** are primarily used in conditions like **schizophrenia** or **Parkinson's disease** (for psychotic symptoms), by blocking dopamine receptors. - This is not the mechanism of action for medications used to treat cognitive symptoms of Alzheimer's disease. *Serotonin reuptake inhibitor* - **Serotonin reuptake inhibitors (SSRIs)** are a class of antidepressants that increase serotonin levels in the brain by blocking its reuptake [3]. - While depression can co-occur with Alzheimer's, SSRIs do not directly address the cognitive decline associated with the disease [3].

Question 766: What are the roles of cholinesterase inhibitors and NMDA receptor antagonists in the treatment of Alzheimer's disease?

A. Cholinesterase inhibitors enhance cognitive function; NMDA antagonists reduce excitotoxicity (Correct Answer)
B. Cholinesterase inhibitors reduce excitotoxicity; NMDA antagonists enhance cognitive function
C. Both target glutamate neurotransmission
D. Both improve memory by increasing acetylcholine

Explanation: ***Cholinesterase inhibitors enhance cognitive function; NMDA antagonists reduce excitotoxicity*** - **Cholinesterase inhibitors** work by increasing the availability of **acetylcholine** in the brain, improving **cholinergic neurotransmission** crucial for **memory and learning**. - **NMDA receptor antagonists** (like memantine) modulate **glutamate activity** by blocking NMDA receptors, preventing **excitotoxicity** and neuronal damage associated with excessive glutamate. *Cholinesterase inhibitors reduce excitotoxicity; NMDA antagonists enhance cognitive function* - **Cholinesterase inhibitors** primarily increase **acetylcholine levels** for cognitive function, not directly reduce excitotoxicity. - **NMDA antagonists** primarily protect neurons from **excitotoxicity**, which secondarily supports cognitive function but isn't their direct mechanism for enhancement. *Both target glutamate neurotransmission* - Only **NMDA receptor antagonists** directly target **glutamate neurotransmission** to reduce excitotoxicity. - **Cholinesterase inhibitors** focus on the **acetylcholine system**, enhancing its availability rather than impacting glutamate directly. *Both improve memory by increasing acetylcholine* - Only **cholinesterase inhibitors** work by increasing **acetylcholine** levels in the brain to improve memory. - **NMDA receptor antagonists** modulate glutamate and do not increase acetylcholine.

Question 767: Which of the following non-depolarizing neuromuscular blockers does not cause the release of histamine?

A. d-tubocurarine
B. Mivacurium
C. Atracurium
D. Vecuronium (Correct Answer)

Explanation: ***Vecuronium*** - **Vecuronium** is an aminosteroid non-depolarizing neuromuscular blocker known for its minimal cardiovascular effects and **lack of histamine release**. - Its chemical structure (lacking quaternary ammonium groups in certain positions) contributes to its **low propensity for histamine release**, making it suitable for patients with reactive airway disease or cardiovascular instability. *d-tubocurarine* - **d-tubocurarine** is a classic non-depolarizing neuromuscular blocker that is well-known for causing significant **histamine release**, leading to **hypotension** and **bronchospasm**. - Due to its side effect profile, it is rarely used in modern clinical practice. *Atracurium* - **Atracurium** is a benzylisoquinolinium non-depolarizing neuromuscular blocker that can cause **histamine release**, particularly with rapid administration or higher doses. - While its histamine-releasing properties are less pronounced than d-tubocurarine, they can still lead to **cutaneous flushing** and **hypotension**. *Mivacurium* - **Mivacurium** is another benzylisoquinolinium non-depolarizing neuromuscular blocker that is known to cause **histamine release**, especially at higher doses or rapid injection rates. - The histamine release from mivacurium is generally dose-dependent and can result in **flushing** and **transient hypotension**.

Question 768: What is the drug of choice for juvenile myoclonic epilepsy?

A. Oxcarbazepine
B. Zonisamide
C. Valproic acid (Correct Answer)
D. Lacosamide

Explanation: ***Valproic acid*** - **Valproic acid** is considered the first-line and most effective treatment for **juvenile myoclonic epilepsy (JME)**, effectively controlling myoclonic, generalized tonic-clonic, and absence seizures common in this syndrome. [1] - It works by increasing **GABA activity**, blocking voltage-gated sodium channels, and inhibiting T-type calcium channels, all of which contribute to its broad-spectrum anticonvulsant effects. *Oxcarbazepine* - **Oxcarbazepine** is a sodium channel blocker primarily used for **focal (partial) seizures** and is generally not effective for generalized epilepsies like JME. - It can sometimes worsen myoclonic seizures or generalized tonic-clonic seizures in patients with JME. *Zonisamide* - **Zonisamide** is a broad-spectrum antiepileptic drug that can be used for various seizure types, including generalized seizures, but it is typically a **second-line agent** or an add-on therapy for JME, not the first-line drug of choice. - Its mechanism involves blocking sodium and T-type calcium channels, but its efficacy in JME is generally considered less robust than valproic acid. *Lacosamide* - **Lacosamide** selectively enhances slow inactivation of voltage-gated sodium channels and is approved primarily for the treatment of **focal-onset seizures**. [2] - It is **not recommended** for juvenile myoclonic epilepsy because it can exacerbate myoclonic seizures and generalized tonic-clonic seizures and has no proven efficacy in this epilepsy syndrome.

Question 769: Which drug is used to reverse the effects of non-depolarizing muscle relaxants?

A. Neostigmine (Correct Answer)
B. Atropine
C. Glycopyrrolate
D. Scopolamine

Explanation: ***Neostigmine*** - Neostigmine is an **acetylcholinesterase inhibitor** that increases the amount of acetylcholine available at the neuromuscular junction. - This increase in acetylcholine outcompetes the non-depolarizing muscle relaxants, thereby reversing their paralytic effects. *Atropine* - Atropine is an **anticholinergic drug** primarily used to counteract the muscarinic side effects of neostigmine, such as bradycardia and increased secretions. - It does not directly reverse the effects of muscle relaxants but is often co-administered with neostigmine to mitigate its parasympathetic effects. *Glycopyrrolate* - Glycopyrrolate is also an **anticholinergic agent** similar to atropine, used to prevent the muscarinic side effects of acetylcholinesterase inhibitors. - It is preferred over atropine in some cases due to its quaternary ammonium structure, which limits its ability to cross the blood-brain barrier, reducing central nervous system side effects. *Scopolamine* - Scopolamine is an **antimuscarinic agent** primarily used for preventing motion sickness and postoperative nausea and vomiting. - While it has anticholinergic properties, it is not used to reverse non-depolarizing muscle relaxants or to counteract the side effects of neostigmine in this context.

Question 770: Which drug is primarily used to lower intraocular pressure in acute angle-closure glaucoma?

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

Explanation: ***Pilocarpine*** - **Pilocarpine** is a **cholinergic agonist** that is the **primary topical drug** for acute angle-closure glaucoma. - It causes **miosis** (pupillary constriction) and contraction of the ciliary muscle, which pulls the peripheral iris away from the trabecular meshwork, thereby **opening the closed angle**. - This directly addresses the **pathophysiology** of angle-closure glaucoma and is administered immediately as **first-line topical therapy**. - Typically given as **pilocarpine 2-4%** every 15 minutes initially. *Acetazolamide* - **Acetazolamide** is a **carbonic anhydrase inhibitor** that rapidly reduces intraocular pressure by decreasing aqueous humor production. - It is an important **adjunctive systemic therapy** used alongside pilocarpine in acute angle-closure glaucoma. - While it provides significant IOP reduction, it does **not address the angle closure** itself, which is the primary pathology. - Given IV or orally (500 mg) as part of comprehensive emergency management. *Timolol* - **Timolol** is a **beta-blocker** that reduces aqueous humor production. - It may be used as **adjunctive topical therapy** in acute angle-closure glaucoma but is not the primary drug. - Its role is secondary to opening the angle and is more commonly used in **chronic open-angle glaucoma**. *Latanoprost* - **Latanoprost** is a **prostaglandin analog** that increases aqueous humor outflow through the **uveoscleral pathway**. - It has a **slow onset of action** (hours to days) and is effective for **chronic open-angle glaucoma**. - It is **not used** in acute angle-closure glaucoma due to its delayed effect and lack of action on the closed angle.

Practice by Chapter

General Anesthetics

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Local Anesthetics

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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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