Central Nervous System Pharmacology — MCQs

Central Nervous System Pharmacology Indian Medical PG Practice Questions and MCQs

Question 771: What is the preferred initial treatment for a patient diagnosed with Parkinson's disease who is under 65 years old and has minimal symptoms?

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

Explanation: ***Dopamine agonists*** - For **younger patients** (under 65) with mild Parkinson's symptoms, dopamine agonists are often preferred as initial therapy. - They tend to cause fewer motor complications compared to levodopa, delaying the onset of **dyskinesias** for several years. *Levodopa* - While highly effective, **levodopa** is typically reserved for older patients or those with more advanced symptoms due to the increased risk of **motor fluctuations** and **dyskinesias** with long-term use, especially in younger individuals. - It is the most potent symptomatic treatment for Parkinson's disease, but its long-term side effects are a concern for younger patients. *MAO-B inhibitors* - **MAO-B inhibitors** are often used as monotherapy for very mild symptoms or as an adjunct therapy to reduce the "off" time in patients already on levodopa. - They provide only modest symptomatic benefit and do not typically offer the same level of symptom control as dopamine agonists or levodopa in initial treatment. *Anticholinergics* - **Anticholinergics** are primarily used to manage **tremor** in younger patients with Parkinson's disease. - They are associated with significant side effects such as cognitive impairment, dry mouth, and constipation, making them less suitable as an initial broad-spectrum treatment, especially in older patients.

Question 772: Which of the following antiepileptic drugs is preferred for treating generalized tonic-clonic seizures?

A. Ethosuximide
B. Gabapentin
C. Valproic acid (Correct Answer)
D. Carbamazepine

Explanation: ***Valproic acid*** - **Valproic acid** is a broad-spectrum antiepileptic drug effective against various seizure types, including **generalized tonic-clonic seizures**. - It is considered the **gold standard** for generalized seizures because it is effective against all types (absence, myoclonic, and tonic-clonic). - It works by increasing GABA levels, blocking voltage-gated sodium channels, and inhibiting T-type calcium channels. *Ethosuximide* - **Ethosuximide** is specifically used for **absence seizures** (petit mal) and is not effective for generalized tonic-clonic seizures. - It primarily acts by blocking **T-type calcium channels** in the thalamus. *Gabapentin* - **Gabapentin** is primarily used for **focal (partial) seizures** and neuropathic pain, not generalized tonic-clonic seizures. - Its mechanism involves modulating the release of neurotransmitters, possibly by binding to the **α2δ subunit of calcium channels**. *Carbamazepine* - **Carbamazepine** is a first-line treatment for **focal (partial) seizures** and is also effective for **generalized tonic-clonic seizures**, though valproic acid is generally preferred for purely generalized seizures. - It works by blocking voltage-gated sodium channels. - It should be **avoided in absence and myoclonic seizures** as it can worsen these seizure types. - Also used for **trigeminal neuralgia**.

Question 773: A patient on donepezil for Alzheimer's disease begins to experience bradycardia. What is the likely mechanism of this side effect?

A. Inhibition of acetylcholinesterase (Correct Answer)
B. Increased GABAergic transmission
C. Blockade of NMDA receptors
D. Increased dopamine release

Explanation: ***Inhibition of acetylcholinesterase*** - Donepezil is an **acetylcholinesterase inhibitor**, meaning it increases the amount of **acetylcholine** in the synaptic cleft. - Increased acetylcholine activity at muscarinic receptors in the heart, particularly **M2 receptors**, leads to **bradycardia** by decreasing the heart rate and conduction velocity. *Increased GABAergic transmission* - **GABA** (gamma-aminobutyric acid) is the primary inhibitory neurotransmitter in the central nervous system and primarily affects neuronal excitability, not directly cardiac rhythm. - Medications that increase GABAergic transmission typically cause **sedation** or **anxiolysis**, and are not directly associated with bradycardia as a primary mechanism. *Blockade of NMDA receptors* - **NMDA receptor blockers** (e.g., memantine) are used in Alzheimer's disease to modulate glutamate activity, but they do not directly influence the cholinergic system or heart rate in a way that causes bradycardia. - Their primary effects are on neuronal excitability and neuroprotection, rather than autonomic cardiac function. *Increased dopamine release* - **Dopamine** acts on alpha, beta, and dopaminergic receptors; its release generally tends to **increase heart rate** and cardiac contractility rather than cause bradycardia. - Increased dopamine is not a mechanism of action for donepezil, which specifically targets acetylcholine.

Question 774: Which of the following acetylcholinesterase inhibitors is most commonly prescribed as first-line therapy for mild to moderate Alzheimer's disease due to its once-daily dosing and favorable side effect profile?

A. Donepezil (Correct Answer)
B. Galantamine
C. Rivastigmine
D. All of the options

Explanation: ***Donepezil*** - It is frequently chosen as a **first-line agent** for mild to moderate Alzheimer's disease due to its **favorable side effect profile** and **once-daily dosing** [1]. - Its long half-life allows for administration once a day, which can improve **patient adherence** to therapy [1]. *Galantamine* - This acetylcholinesterase inhibitor typically requires **twice-daily dosing**, which is less convenient than donepezil's once-daily regimen [2]. - While effective, it does not hold the same **first-line preference** as donepezil due to its more frequent administration [2]. *Rivastigmine* - Rivastigmine is available in oral and transdermal patch formulations, but its oral form often requires **twice-daily dosing** or more [2]. - Its side effect profile can be more pronounced, particularly **gastrointestinal side effects**, compared to donepezil [2]. *All of the options* - While all listed options are acetylcholinesterase inhibitors used in Alzheimer's disease, **Donepezil** stands out as the most common first-line choice due to its once-daily dosing and well-tolerated profile [1], [2]. - The other options have different dosing schedules or side effect profiles that make them less universally preferred as initial therapy [2].

Question 775: A 28-year-old woman with a history of seizures is prescribed a classic anticonvulsant that primarily works by inhibiting voltage-gated sodium channels. Which drug is most likely being prescribed?

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

Explanation: ***Phenytoin*** - **Phenytoin** is the **classic prototype anticonvulsant** [1] that primarily works by **blocking voltage-gated sodium channels**, thus stabilizing the neuronal membrane and preventing repetitive firing [2]. - It is effective in treating various seizure types, including **focal** and **generalized tonic-clonic seizures** [1]. - As the traditional first-line agent in this class, it is the most likely answer when referring to a "classic" sodium channel blocker [1]. *Carbamazepine* - While **carbamazepine** also works by **blocking voltage-gated sodium channels** [2], it is structurally related to tricyclic antidepressants and came after phenytoin. - It's often used for **focal seizures** and **trigeminal neuralgia**. - Considered an important alternative but not the "classic" prototype [1]. *Valproate* - **Valproate** has **multiple mechanisms of action**, including inhibiting **GABA transaminase** (increasing GABA levels), blocking **sodium channels**, and modulating **T-type calcium channels** [2]. - Its broad spectrum is useful for both **focal** and **generalized seizures**, including absence seizures. - Not primarily classified as a sodium channel blocker due to its multiple mechanisms. *Lamotrigine* - **Lamotrigine** is a **newer anticonvulsant** [1] that inhibits presynaptic **voltage-gated sodium channels**, reducing the release of excitatory neurotransmitters like glutamate [2]. - It is effective against various seizure types, including **focal**, **generalized tonic-clonic**, and seizures associated with **Lennox-Gastaut syndrome**. - Developed later as a second-generation antiepileptic drug [1].

Question 776: What is the first-line treatment for a patient presenting with an acute dystonic reaction?

A. Benzodiazepines
B. Anticholinergics (Correct Answer)
C. Beta-blockers
D. Dopamine agonists

Explanation: ***Anticholinergics*** - **Anticholinergic medications**, such as **benztropine** or **diphenhydramine**, are the **first-line treatment** for acute dystonic reactions. - They work by **blocking muscarinic acetylcholine receptors**, thereby re-establishing the balance between dopamine and acetylcholine in the basal ganglia, which is disrupted in dystonia. *Benzodiazepines* - While benzodiazepines can provide some symptomatic relief by reducing muscle spasms and anxiety, they are **not the first-line treatment** for the underlying neurological cause of acute dystonia. - They primarily act on **GABA receptors**, promoting muscle relaxation, but do not directly address the dopamine-acetylcholine imbalance. *Beta-blockers* - **Beta-blockers** are primarily used to treat conditions like **hypertension**, **anxiety**, or **essential tremor**, and are **not effective** for acute dystonic reactions. - They work by blocking beta-adrenergic receptors and have no direct role in the pathophysiology of dystonia. *Dopamine agonists* - **Dopamine agonists** are typically used to **increase dopamine activity**, as seen in conditions like **Parkinson's disease**. - Acute dystonic reactions are often caused by **dopamine receptor blockade** (e.g., by antipsychotics), so increasing dopamine agonism would generally be **contraindicated** or ineffective.

Question 777: A patient with Parkinson's disease is given a dopamine agonist to manage motor symptoms by directly stimulating dopamine receptors. Which drug corresponds to this description?

A. Levodopa
B. Selegiline
C. Entacapone
D. Pramipexole (Correct Answer)

Explanation: ***Pramipexole*** - **Pramipexole** is a commonly used **non-ergot dopamine agonist** that **directly stimulates dopamine D2 and D3 receptors** in the brain. - It is effective in managing motor symptoms of **Parkinson's disease** by mimicking the effects of dopamine, particularly in early-stage disease or as an adjunct to levodopa. - Unlike levodopa, it does not require enzymatic conversion and directly activates dopamine receptors. *Levodopa* - **Levodopa** is a **dopamine precursor** that is converted into dopamine in the brain via aromatic L-amino acid decarboxylase (AADC). - It works by **replenishing deficient dopamine levels** rather than directly stimulating dopamine receptors. - It is the most effective symptomatic treatment for Parkinson's disease but is **not a dopamine agonist**. *Selegiline* - **Selegiline** is a **selective monoamine oxidase-B (MAO-B) inhibitor** that prevents the breakdown of dopamine in the brain. - It **increases dopamine availability** by blocking its metabolism but does not directly stimulate dopamine receptors. - It is used as an adjunct therapy to enhance the effects of endogenous or exogenous dopamine. *Entacapone* - **Entacapone** is a **catechol-O-methyltransferase (COMT) inhibitor** that prevents the peripheral breakdown of levodopa. - This action **prolongs the half-life of levodopa**, allowing more to cross the blood-brain barrier, but it does not directly stimulate dopamine receptors. - It is always used in combination with levodopa/carbidopa to enhance levodopa's effectiveness.

Question 778: A 35-year-old male is prescribed morphine for severe pain. What is a common side effect of morphine?

A. Hypertension
B. Diarrhea
C. Sedation (Correct Answer)
D. Polyuria

Explanation: ***Sedation*** - **Morphine** is an **opioid analgesic** that acts on **central nervous system** opioid receptors, leading to a depressant effect, which manifests as sedation. - This side effect is due to its action on the **brainstem**, affecting various physiological functions including wakefulness. *Hypertension* - **Morphine** typically causes **hypotension** rather than hypertension due to its **vasodilatory effects**. - It can release **histamine**, which contributes to vasodilation and a drop in blood pressure. *Diarrhea* - **Morphine** is well-known for causing **constipation** by decreasing **gastrointestinal motility** and increasing anal sphincter tone. - It increases **non-propulsive contractions** and reduces **propulsive contractions** in the gut, leading to stool retention. *Polyuria* - **Morphine** can actually cause **oliguria** or **urinary retention** due to increased **antidiuretic hormone (ADH) secretion** and contraction of the **bladder sphincter**. - It affects the **renal system** by altering hormonal regulation and smooth muscle tone, not by increasing urine output.

Question 779: What is the first-line drug for the prophylaxis of cluster headaches?

A. Sumatriptan
B. Verapamil (Correct Answer)
C. Prednisone
D. Lithium

Explanation: ***Verapamil*** - **Verapamil**, a **non-dihydropyridine calcium channel blocker**, is the **first-line prophylactic agent** for chronic cluster headaches due to its efficacy in reducing headache frequency and severity. - It works by **stabilizing neuronal excitability** and has a **better safety profile** for long-term use compared to acute treatments. *Sumatriptan* - **Sumatriptan** is an **abortive therapy** used for the acute treatment of cluster headache attacks, not for long-term prophylaxis. - It acts as a **serotonin 5-HT1B/1D receptor agonist** to constrict cranial blood vessels and inhibit pain pathways. *Prednisone* - **Prednisone**, a corticosteroid, can be used as a **short-term bridge therapy** to provide rapid relief during the initiation of a long-term prophylactic agent but is not suitable for routine chronic prophylaxis due to significant side effects. - Its mechanism involves **reducing inflammation**, which can temporarily alleviate headache symptoms. *Lithium* - **Lithium** is an **alternative prophylactic agent** for cluster headaches, particularly effective in **chronic cluster headache** that is refractory to verapamil. - It is considered **second-line** due to its narrow therapeutic index and the need for regular blood level monitoring.

Question 780: Ketamine acts on which of the following?

A. NMDA receptor (Correct Answer)
B. Glycine receptor
C. GABAa receptor
D. Ach receptor

Explanation: ***NMDA receptor*** - **Ketamine** primarily acts as an **N-methyl-D-aspartate (NMDA) receptor antagonist**, blocking the effects of **glutamate**. - This action leads to its **dissociative anesthetic** effects, including analgesia, amnesia, and a cataleptic state. *Glycine receptor* - The **glycine receptor** is an inhibitory ionotropic receptor, primarily found in the **spinal cord** and brainstem. - Its activation leads to **hyperpolarization** and a decrease in neuronal excitability, a mechanism distinct from ketamine's action. *GABAa receptor* - The **GABAa receptor** is the primary inhibitory neurotransmitter receptor in the brain, and drugs like **benzodiazepines** and **barbiturates** act on it to produce sedation. - While ketamine has some indirect GABAergic effects at high doses, its primary mechanism of action is not through direct binding to GABAa receptors. *Ach receptor* - The **acetylcholine (Ach) receptor** is involved in various functions, including muscle contraction (nicotinic receptors) and parasympathetic responses (muscarinic receptors). - Drugs like **atropine** and **neostigmine** target these receptors, which are not the primary site of action for **ketamine**.

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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