Central Nervous System Pharmacology Practice Questions

Q: Varenicline acts by?

Partial nicotine receptor agonist. **Explanation:** **Varenicline** is a high-yield drug in CNS pharmacology, specifically used for **smoking cessation**. Its mechanism of action is centered on its role as a **selective partial agonist** at the **α4β2 nicotinic acetylcholine receptors (nAChR)** located in the brain. 1. **Why Option A is correct:** As a **partial agonist**, varenicline provides a dual benefit. It stimulates the nicotinic receptors enough to maintain a low level of dopamine release, which helps **reduce withdrawal symptoms** and cravings. Simultaneously, because it has a high affinity for the receptor, it blocks nicotine from binding. 2. **Why Option B and C are incorrect:** While varenicline does have "antagonist-like" effects by blocking nicotine, it is pharmacologically classified as a **partial agonist**, not a pure antagonist. Option C is a distractor; although partial agonists exhibit both agonistic and antagonistic properties depending on the presence of a full agonist, the standard pharmacological classification for varenicline is a "Partial Agonist." **High-Yield Clinical Pearls for NEET-PG:** * **Indication:** First-line agent for smoking cessation (more effective than Bupropion). * **Side Effects:** The most common side effect is **nausea**. However, the most serious "red flag" side effects are **neuropsychiatric symptoms**, including suicidal ideation, depression, and vivid dreams/nightmares. * **Comparison:** Unlike **Bupropion** (which inhibits Dopamine and NE reuptake), Varenicline acts directly on the nicotinic receptor. * **Route:** Administered orally.

Q: Which of the following drugs is NOT used in migraine prophylaxis?

Sumatriptan. ### Explanation The management of migraine is divided into two categories: **Abortive (Acute) therapy** and **Prophylactic (Preventive) therapy**. **Why Sumatriptan is the correct answer:** Sumatriptan is a **5-HT$_{1B/1D}$ receptor agonist**. Its primary mechanism involves vasoconstriction of dilated cranial blood vessels and inhibition of pro-inflammatory neuropeptide release (Substance P, CGRP) from trigeminal nerve endings. Because of its rapid onset and short duration of action, it is used exclusively for the **acute abortive treatment** of migraine attacks, not for prophylaxis. **Analysis of other options (Prophylactic agents):** * **Propranolol (Option B):** A non-selective beta-blocker and the **drug of choice** for migraine prophylaxis. It works by stabilizing vascular tone and increasing the threshold for migraine triggers. * **Flunarizine (Option A):** A non-selective **Calcium Channel Blocker (CCB)** with additional H1-blocking activity. It is highly effective in reducing the frequency of attacks. * **Cyproheptadine (Option C):** A combined **5-HT$_2$ and H$_1$ receptor antagonist**. It is particularly used for migraine prophylaxis in **children**. **NEET-PG High-Yield Pearls:** 1. **Prophylaxis Criteria:** Indicated if attacks occur >2–3 times/month or are severe/disabling. 2. **First-line Prophylactic Drugs:** Beta-blockers (Propranolol), Anticonvulsants (Topiramate, Valproate), and TCAs (Amitriptyline). 3. **Newer Agents:** **CGRP Antagonists** (e.g., Erenumab) are used for prophylaxis, while **Gepants** (e.g., Rimegepant) and **Ditans** (e.g., Lasmiditan) are used for acute attacks. 4. **Contraindication:** Triptans are contraindicated in patients with Ischemic Heart Disease (IHD) or Prinzmetal angina due to their vasoconstrictive properties.

Q: Which of the following drugs inhibits the release of calcium from the sarcoplasmic reticulum?

Dantrolene. **Explanation:** **Dantrolene (Correct Answer):** Dantrolene is a peripherally acting muscle relaxant that directly interferes with excitation-contraction coupling in skeletal muscle. It acts by binding to the **Ryanodine Receptor 1 (RyR1)** located on the sarcoplasmic reticulum (SR). This binding inhibits the release of calcium ions from the SR into the cytosol, thereby preventing muscle contraction. This unique mechanism makes it the drug of choice for **Malignant Hyperthermia**, where there is an uncontrolled release of calcium. **Incorrect Options:** * **Caffeine:** Unlike Dantrolene, caffeine actually **stimulates** the Ryanodine receptors, promoting the release of calcium from the SR. In vitro, the "Caffeine-Halothane Contracture Test" is used to diagnose susceptibility to malignant hyperthermia. * **Rocuronium:** This is a **non-depolarizing neuromuscular blocker** that acts at the neuromuscular junction (NMJ) by competitively antagonizing nicotinic acetylcholine receptors ($N_m$). It does not act directly on the SR. * **Succinylcholine:** This is a **depolarizing neuromuscular blocker** that acts as an agonist at $N_m$ receptors, causing persistent depolarization. Notably, it is a known trigger for malignant hyperthermia in susceptible individuals. **NEET-PG High-Yield Pearls:** * **Drug of Choice:** Dantrolene is used for Malignant Hyperthermia, Neuroleptic Malignant Syndrome (NMS), and spasticity associated with upper motor neuron lesions. * **Side Effect:** The most significant chronic side effect of Dantrolene is **hepatotoxicity** (monitor LFTs). * **Malignant Hyperthermia Trigger:** Often triggered by volatile anesthetics (e.g., Halothane) and Succinylcholine due to mutations in the *RYR1* gene.

Q: All of the following drugs cause hyperprolactinemia EXCEPT:

Bromocriptine. **Explanation:** The regulation of prolactin secretion is primarily under the inhibitory control of **Dopamine**, which acts on **D2 receptors** in the anterior pituitary (Tuberoinfundibular pathway). Any drug that increases dopaminergic activity will decrease prolactin, while any drug that blocks D2 receptors will cause **hyperprolactinemia**. **Why Bromocriptine is the Correct Answer:** Bromocriptine is a potent **D2 receptor agonist**. By stimulating the dopamine receptors in the pituitary, it mimics the natural inhibitory effect of dopamine, thereby **decreasing** prolactin levels. It is clinically used in the management of prolactinomas and galactorrhea. **Why the Other Options are Incorrect:** * **Haloperidol & Chlorpromazine:** These are typical antipsychotics that act by blocking D2 receptors in the brain. By blocking these receptors in the tuberoinfundibular pathway, they remove the "dopamine brake," leading to significantly elevated prolactin levels. * **Metoclopramide:** This is a prokinetic and antiemetic drug that also acts as a central D2 receptor antagonist. It is a well-known cause of drug-induced hyperprolactinemia and gynecomastia. **High-Yield NEET-PG Pearls:** 1. **Dopamine = Prolactin Inhibiting Hormone (PIH).** 2. **Tuberoinfundibular Pathway:** The specific dopaminergic pathway responsible for prolactin regulation. 3. **Other drugs causing hyperprolactinemia:** Reserpine (depletes dopamine), Methyldopa, Verapamil, and SSRIs. 4. **Clinical Presentation:** In females, hyperprolactinemia presents as galactorrhea, amenorrhea, and infertility; in males, it causes gynecomastia and erectile dysfunction.

Q: A patient with ischemic heart disease is diagnosed with migraine. Which drug is indicated in this case?

Butorphanol. **Explanation:** The management of migraine in patients with **Ischemic Heart Disease (IHD)** requires caution because many standard migraine medications cause systemic vasoconstriction, which can exacerbate myocardial ischemia. **Why Butorphanol is correct:** Butorphanol is a mixed opioid agonist-antagonist (κ-agonist and μ-partial agonist/antagonist). Unlike specific anti-migraine drugs, it does not act on serotonin (5-HT) receptors that cause vasoconstriction. It provides potent analgesia for acute migraine attacks without compromising coronary blood flow, making it a safer alternative for patients with cardiovascular contraindications. **Why the other options are incorrect:** * **Triptans (e.g., Sumatriptan):** These are 5-HT$_{1B/1D}$ agonists. While they effectively constrict cranial vessels, they also cause **coronary vasospasm**. They are strictly contraindicated in patients with IHD, Prinzmetal angina, or uncontrolled hypertension. * **Ergotamines:** These act on 5-HT$_{1}$, 5-HT$_{2}$, and α-adrenergic receptors. They are potent, long-acting vasoconstrictors and are contraindicated in IHD and peripheral vascular disease. * **Propranolol:** While used for migraine **prophylaxis**, it is not indicated for the treatment of an acute attack. Furthermore, in certain cardiac conditions (like vasospastic angina), non-selective beta-blockers can worsen coronary vasoconstriction due to unopposed α-activity. **High-Yield Clinical Pearls for NEET-PG:** * **DOC for Acute Migraine:** Triptans (Sumatriptan). * **DOC for Migraine Prophylaxis:** Propranolol (others include Topiramate, Amitriptyline, and Valproate). * **Newer Drugs (Safe in IHD):** **Lasmiditan** (5-HT$_{1F}$ agonist) and **Gepants** (CGRP antagonists like Rimegepant) are preferred modern alternatives for patients with cardiovascular risks as they do not cause vasoconstriction.

Q: Which drug is primarily used for the treatment of absence seizures?

Lamotrigine. **Explanation:** The drug of choice for **Absence Seizures** (Petit Mal) is traditionally **Ethosuximide** (for pure absence) or **Sodium Valproate** (if associated with tonic-clonic seizures). However, among the given options, **Lamotrigine** is the correct answer as it is a broad-spectrum antiepileptic effective against absence seizures. **1. Why Lamotrigine is Correct:** Lamotrigine acts by blocking voltage-gated sodium channels and inhibiting the release of excitatory neurotransmitters (glutamate and aspartate) [1]. It also has some activity against T-type calcium channels, which are central to the pathophysiology of absence seizures. It is considered a first-line alternative, especially in women of childbearing age, due to its better safety profile compared to Valproate. **2. Why Other Options are Incorrect:** * **Carbamazepine & Phenytoin:** These are narrow-spectrum drugs that block sodium channels. They are strictly **contraindicated** in absence seizures as they can paradoxically worsen the condition or precipitate absence status. * **Vigabatrin:** This drug acts by irreversibly inhibiting GABA transaminase. It is primarily used for Infantile Spasms (West Syndrome) and focal seizures [3]. It is not effective for absence seizures. **Clinical Pearls for NEET-PG:** * **Drug of Choice (DOC):** Ethosuximide (Pure Absence); Valproate (Absence + GTCS). * **Mechanism of Ethosuximide:** Inhibition of **T-type Ca²⁺ channels** in thalamic neurons [2]. * **EEG Finding:** Classic **3 Hz spike-and-wave** discharges. * **Avoid in Absence:** Phenytoin, Carbamazepine, Oxcarbazepine, and Tiagabine (they aggravate the seizure) [2]. * **Lamotrigine Side Effect:** Watch for **Stevens-Johnson Syndrome (SJS)**; the dose must be titrated slowly.

Q: Which of the following is a preferred opioid for pain control in terminally ill cancer patients?

Fentanyl. **Explanation:** **Fentanyl (Option B)** is the preferred opioid for chronic pain management in terminally ill cancer patients, primarily due to its availability as a **transdermal patch**. This delivery system provides continuous, stable analgesia for up to 72 hours, ensuring better patient compliance and avoiding the "peak and valley" effect of oral medications. It is highly lipophilic, potent, and lacks active metabolites, making it safer in patients with renal impairment—a common complication in advanced malignancy. **Why other options are incorrect:** * **Pethidine (Option A):** It is contraindicated for chronic cancer pain. Its metabolite, **norpethidine**, has a long half-life and is neurotoxic, leading to tremors, myoclonus, and seizures, especially with repetitive dosing. * **Methadone (Option C):** While used for chronic pain, it has a very long and unpredictable half-life (15–60 hours), leading to a high risk of cumulative toxicity and respiratory depression. It requires complex titration. * **Remifentanil (Option D):** It has an ultra-short duration of action (metabolized by plasma esterases). It is used exclusively for induction/maintenance of anesthesia via continuous infusion and is unsuitable for long-term outpatient pain control. **High-Yield Clinical Pearls for NEET-PG:** * **Drug of Choice (DOC)** for terminal cancer pain (WHO Ladder Step 3): **Morphine** (Oral) is the gold standard; however, **Fentanyl** is the preferred long-term transdermal option. * **Renal Failure:** Fentanyl and Buprenorphine are the safest opioids as they do not have active metabolites excreted by the kidney (unlike Morphine and Hydromorphone). * **Miosis & Constipation:** These are two side effects of opioids to which **tolerance never develops**.

Question 1

Varenicline acts by?

Accepted Answer

Partial nicotine receptor agonist

Answer

Nicotine receptor antagonist

Answer

Both agonist and antagonist at nicotine receptor

Answer

None of the above

Question 2

What is the mode of action of depolarizing and non-depolarizing neuromuscular blockers?

Accepted Answer

Depolarizing - causes persistent depolarization; non-depolarizing - competitive inhibition

Answer

Both are competitive inhibitors

Answer

Non-depolarizing - no repolarization; depolarizing - no depolarization

Answer

Depolarizing - persistent depolarization; non-depolarizing - no repolarization

Question 3

Which of the following drugs is NOT used in migraine prophylaxis?

Accepted Answer

Sumatriptan

Answer

Flunarizine

Answer

Propranolol

Answer

Cyproheptadine

Question 4

Carbachol acts as

Accepted Answer

Agonist for M3 receptors

Answer

Agonist for M2 receptors

Answer

Agonist for M1 receptors

Answer

Antagonist for M3 receptors

Question 5

Which of the following drugs inhibits the release of calcium from the sarcoplasmic reticulum?

Accepted Answer

Dantrolene

Answer

Caffeine

Answer

Rocuronium

Answer

Succinylcholine

Question 6

All of the following drugs cause hyperprolactinemia EXCEPT:

Accepted Answer

Bromocriptine

Answer

Haloperidol

Answer

Chlorpromazine

Answer

Metoclopramide

Question 7

A patient with ischemic heart disease is diagnosed with migraine. Which drug is indicated in this case?

Accepted Answer

Butorphanol

Answer

Propranolol

Answer

Triptans

Answer

Ergotamines

Question 8

Which drug is primarily used for the treatment of absence seizures?

Accepted Answer

Lamotrigine

Answer

Carbamazepine

Answer

Phenytoin

Answer

Vigabatrine

Question 9

Which of the following is a preferred opioid for pain control in terminally ill cancer patients?

Accepted Answer

Fentanyl

Answer

Pethidine

Answer

Methadone

Answer

Remifentanyl

Question 10

What is the primary therapeutic strategy for dopamine deficiency in the substantia nigra in Parkinson's disease?

Accepted Answer

Provision of metabolites in the tyrosine pathway

Answer

Feedback inhibition of dopamine oxidation

Answer

Competitive inhibition of dopamine biosynthesis from histidine

Answer

Stimulation of monoamine oxidase

Central Nervous System Pharmacology — MCQs

Central Nervous System Pharmacology — MCQs

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