Central Nervous System Pharmacology — MCQs

Central Nervous System Pharmacology Indian Medical PG Practice Questions and MCQs

Question 741: Angel dust is:

A. LSD
B. Cannabis
C. Phencyclidine (Correct Answer)
D. Morphine

Explanation: ***Correct: Phencyclidine*** - **Phencyclidine (PCP)** is commonly known by the street name **"angel dust"** - It is a **dissociative anesthetic** with hallucinogenic and neurotoxic effects - Acts primarily as an **NMDA receptor antagonist** *Incorrect: LSD* - **LSD (lysergic acid diethylamide)** is a classic hallucinogen with the street name "acid," not angel dust - It primarily affects **serotonin receptors (5-HT2A)** and causes profound alterations in perception and thought - Chemically and pharmacologically distinct from PCP *Incorrect: Cannabis* - **Cannabis** is a psychoactive drug derived from the *Cannabis* plant, commonly known as marijuana or weed - Its active compound **THC (tetrahydrocannabinol)** produces euphoric and relaxing effects through cannabinoid receptors - Not related to the street name "angel dust" *Incorrect: Morphine* - **Morphine** is a potent **opioid analgesic** used for pain relief - Acts as a **CNS depressant** through mu-opioid receptors - Unlike PCP's dissociative and stimulant effects, morphine produces sedation and analgesia

Question 742: A boy is planning to travel by bus. Which of the following drugs can be used to prevent motion sickness in this person?

A. Fexofenadine
B. Promethazine (Correct Answer)
C. Loratadine
D. Cetirizine

Explanation: **Promethazine** - **Promethazine** is an **H1 antihistamine** with significant **anticholinergic** properties that effectively blocks muscarinic receptors in the **vestibular system**, making it highly effective for preventing motion sickness. - Its **sedating effects** are also beneficial in relieving the discomfort associated with motion sickness. *Fexofenadine* - **Fexofenadine** is a **second-generation H1 antihistamine** that is **non-sedating** and has minimal anticholinergic activity. - While effective for allergies, its lack of central nervous system penetration and anticholinergic action makes it **ineffective for motion sickness**. *Loratadine* - **Loratadine** is another **second-generation H1 antihistamine**, known for being **non-sedating** and having limited entry into the central nervous system. - It does not possess the significant anticholinergic properties necessary to prevent the **vestibular disturbances** that cause motion sickness. *Cetirizine* - **Cetirizine** is a **second-generation H1 antihistamine** that has **moderate sedative effects** (more than other second-generation agents) and some CNS penetration, but lacks the significant **anticholinergic activity** required for motion sickness prevention. - It is primarily used for allergies and is **not recommended** for the prevention or treatment of motion sickness.

Question 743: Which of the following drugs is used for smoking cessation?

A. Gabapentin
B. Acamprosate
C. Nalmefene
D. Varenicline (Correct Answer)

Explanation: ***Varenicline*** - **Varenicline** is a **partial agonist** at the **α4β2 nicotinic acetylcholine receptor**, reducing cravings and withdrawal symptoms while decreasing the rewarding effects of nicotine [2]. - It is a first-line pharmacotherapy for **smoking cessation**, often initiated a week before the target quit date. *Gabapentin* - **Gabapentin** is primarily an **anticonvulsant** and is also used to treat **neuropathic pain**. - It is not indicated for **smoking cessation** and acts by modulating **GABAergic neurotransmission**, unrelated to nicotine dependence. *Acamprosate* - **Acamprosate** is used to maintain **abstinence from alcohol** in patients with alcohol dependence. - Its mechanism involves restoring the balance between **excitation and inhibition** in the brain, which is not directly applicable to nicotine dependence. *Nalmefene* - **Nalmefene** is an **opioid system modulator** used for reducing **alcohol consumption** in adults with alcohol dependence [1]. - It acts as an **opioid receptor antagonist**, a mechanism distinct from the neurotransmitter systems involved in nicotine addiction [1].

Question 744: Knockout drops are:

A. Chloral hydrate (Correct Answer)
B. Kerosene
C. Paraldehyde
D. Turpentine

Explanation: ***Chloral hydrate*** - **Chloral hydrate** is a sedative-hypnotic substance historically used as "knockout drops" due to its quick action in inducing sleep or unconsciousness. - Its use has largely been replaced by safer alternatives due to its narrow therapeutic index and potential for respiratory depression and cardiac arrhythmias. *Kerosene* - **Kerosene** is a flammable hydrocarbon liquid primarily used as fuel or solvent, not as a sedative or hypnotic agent. - Ingestion of kerosene is highly toxic and can cause chemical pneumonitis and gastrointestinal irritation. *Paraldehyde* - **Paraldehyde** is an older sedative and hypnotic drug, but it is not typically referred to as "knockout drops." - It has a very pungent odor and taste, which would make surreptitious administration difficult, and is generally avoided in modern medical practice. *Turpentine* - **Turpentine** is a distillate of pine resin used as a solvent or cleaner, and historically as a liniment or anthelminthic. - It is highly toxic if ingested and can cause severe gastrointestinal distress, kidney damage, and central nervous system depression, but it is not a sedative-hypnotic.

Question 745: Which of the following is not an ESTER?

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

Explanation: ***Bupivacaine*** - Bupivacaine is an **amide-type local anesthetic** because it contains an amide linkage in its chemical structure. - Amide-type local anesthetics are metabolized in the liver, generally having a **longer duration of action** and a lower risk of allergic reactions compared to esters. *Benzocaine* - Benzocaine is an **ester-type local anesthetic**, characterized by an ester linkage that connects the aromatic ring and the amine group, though it lacks a tertiary amine. - It is typically used for **topical applications** due to its poor water solubility and rapid metabolism by plasma esterases. *Amethocaine* - Amethocaine (also known as tetracaine) is an **ester-type local anesthetic**, identifiable by its ester bond. - It has a relatively **long duration of action** for an ester and is often used for spinal anesthesia and topical applications. *Procaine* - Procaine is an **ester-type local anesthetic**, containing the characteristic ester linkage in its chemical structure. - It was one of the first local anesthetics discovered and has a **short duration of action** due to rapid metabolism by plasma pseudocholinesterase.

Question 746: True about MDMA:

A. It is a cocaine congener
B. Methadone is used to treat withdrawal symptoms
C. Ecstasy is another name for it (Correct Answer)
D. Causes parkinsonism like syndrome

Explanation: Ecstasy is another name for it - MDMA (3,4-methylenedioxymethamphetamine) is widely known by its street name, Ecstasy [1]. - This name refers to its profound empathogenic effects and sense of well-being it often induces. It is a cocaine congener - MDMA is an amphetamine derivative and acts primarily on serotonin, dopamine, and norepinephrine systems, distinct from cocaine's primary action as a reuptake inhibitor [1], [2]. - While both MDMA and cocaine are stimulants, their chemical structures and primary mechanisms of action are different; MDMA is a substituted amphetamine [1]. Methadone is used to treat withdrawal symptoms - Methadone is an opioid agonist primarily used in the management of opioid dependence and withdrawal symptoms [3]. - MDMA withdrawal symptoms are typically managed with supportive care, focusing on symptom relief and psychological support, as there is no specific pharmacological treatment like methadone for MDMA withdrawal [3]. Causes parkinsonism like syndrome - While MDMA can cause neurotoxicity, particularly affecting serotonergic neurons, it is not typically associated with a direct parkinsonism-like syndrome [2]. - Parkinsonism is primarily linked to dopaminergic system damage, often seen with certain neuroleptics or drugs like MPTP, not MDMA.

Question 747: Which of the following nerve fibre types is least susceptible to LA blockade?

A. B fibers
B. A beta
C. C fibers
D. A alpha (Correct Answer)

Explanation: **A alpha** - **A alpha fibers** are the **largest** and most heavily myelinated nerve fibers, responsible for **motor function** and **proprioception**. - Due to their large diameter and thick myelination, they have the **highest conduction velocity** and are the **least susceptible to local anesthetic blockade**, requiring higher concentrations or longer exposure times. *B fibers* - **B fibers** are **preganglionic autonomic fibers** that are myelinated but of relatively small diameter. - They are generally **highly sensitive to local anesthetics**, often being blocked even before A-delta and C fibers, due to their specific physiologic properties like repetitive firing and length of node of Ranvier. *C fibers* - **C fibers** are **unmyelinated** and have the **smallest diameter**, transmitting **pain, temperature, and autonomic information**. - Despite being unmyelinated, their small diameter makes them **highly sensitive to local anesthetics**, as the drug can easily penetrate to block sodium channels. *A beta* - **A beta fibers** are large, myelinated fibers involved in transmitting **touch and pressure sensations**. - While myelinated, they are **smaller than A-alpha fibers** and thus more susceptible to local anesthetic blockade than A-alpha, but less so than C or B fibers.

Question 748: Which anti-epileptic drug is most likely to cause aplastic anemia?

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

Explanation: ***Carbamazepine*** - **Carbamazepine** is an anti-epileptic drug that can cause **aplastic anemia** as a rare but serious adverse effect. It is also known to cause other hematological side effects like leukopenia and thrombocytopenia. - Regular monitoring of **complete blood counts** is recommended, especially during the initial phases of treatment, due to this risk. *Phenytoin* - While **phenytoin** can cause various adverse effects, including **folate deficiency** leading to megaloblastic anemia, it is not typically associated with **aplastic anemia**. - Other common side effects include gingival hyperplasia, hirsutism, and Stevens-Johnson syndrome. *Levetiracetam* - **Levetiracetam** is generally well-tolerated and is rarely associated with severe hematological adverse events like **aplastic anemia**. - Its most common side effects are somnolence, asthenia, and behavioral changes. *Valproate* - **Valproate** can cause **thrombocytopenia** and, in rare instances, bone marrow suppression, but it is not a primary cause of **aplastic anemia**. - Its most concerning adverse effects include hepatotoxicity and pancreatitis.

Question 749: A 50-year-old with Parkinson's disease is on levodopa. Adding which drug helps manage 'wearing-off' effects?

A. Entacapone (Correct Answer)
B. Amantadine
C. Selegiline
D. Bromocriptine

Explanation: ***Entacapone*** - **Entacapone** is a **COMT inhibitor** that prolongs the action of **levodopa** in the brain by preventing its peripheral breakdown. - This effectively reduces the "wearing-off" phenomenon, where the effects of levodopa diminish before the next dose. *Amantadine* - **Amantadine** is primarily used to treat **dyskinesias** associated with long-term levodopa therapy in Parkinson's disease. - While it has some dopaminergic activity, it is not the primary choice for managing **"wearing-off" fluctuations**. *Selegiline* - **Selegiline** is an **MAO-B inhibitor** that prevents the breakdown of dopamine in the brain, offering mild symptomatic benefit. - It's typically used in early Parkinson's or as an adjunct, but less effective for **"wearing-off"** compared to COMT inhibitors. *Bromocriptine* - **Bromocriptine** is a **dopamine agonist** that directly stimulates dopamine receptors. - It can be used for motor fluctuations but is more commonly associated with side effects and is generally less preferred than newer dopamine agonists for advanced Parkinson's.

Question 750: A medical student presented to the ED with protracted vomiting. For this he was given an anti-emetic drug following which he developed abnormal posturing. Which of the following is the most likely drug to be given to the patient?

A. Ondansetron
B. Domperidone
C. Dexamethasone
D. Metoclopramide (Correct Answer)

Explanation: ***Metoclopramide*** - **Metoclopramide** is a **dopamine D2 receptor antagonist** that can cause **extrapyramidal symptoms (EPS)**, such as abnormal posturing (dystonia), due to its central action. - This adverse effect is more common with higher doses or in susceptible individuals, and the scenario directly describes it as a consequence of the antiemetic. *Ondansetron* - **Ondansetron** is a **5-HT3 receptor antagonist** primarily used for nausea and vomiting, particularly chemotherapy-induced. - It works **peripherally and centrally** but its side effect profile does not typically include extrapyramidal symptoms like abnormal posturing. *Domperidone* - **Domperidone** is also a **dopamine D2 receptor antagonist**, but it has **limited penetration across the blood-brain barrier**. - Due to its predominantly peripheral action, it causes **fewer central nervous system side effects**, including extrapyramidal symptoms, compared to metoclopramide. *Dexamethasone* - **Dexamethasone** is a **corticosteroid** with antiemetic properties, often used in conjunction with other antiemetics, especially in chemotherapy. - Its mechanism is not related to dopamine receptors, and it **does not typically cause extrapyramidal symptoms or abnormal posturing**.

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

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