Central Nervous System Pharmacology — MCQs

Central Nervous System Pharmacology Indian Medical PG Practice Questions and MCQs

Question 401: What is the first-line treatment for generalized onset tonic-clonic seizures?

A. Lamotrigine (Correct Answer)
B. Phenytoin
C. Levetiracetam
D. Ethosuximide

Explanation: **Explanation:** The management of Generalized Tonic-Clonic Seizures (GTCS) has evolved, with a shift toward broad-spectrum Antiepileptic Drugs (AEDs) that offer better tolerability and fewer drug interactions. **Why Lamotrigine is Correct:** **Lamotrigine** is currently considered a first-line treatment for generalized onset tonic-clonic seizures. It acts by blocking voltage-gated sodium channels and inhibiting the release of glutamate. It is preferred due to its broad-spectrum efficacy and favorable side-effect profile compared to older agents. Notably, it is also a first-line choice in pregnancy (though doses may need adjustment). While **Valproate** was historically the "gold standard," Lamotrigine and Levetiracetam are now preferred first-line options, especially in females of childbearing age due to Valproate’s teratogenicity. **Analysis of Incorrect Options:** * **Phenytoin:** While effective for GTCS, it is no longer first-line due to its non-linear (zero-order) kinetics, narrow therapeutic index, and significant long-term side effects (gingival hyperplasia, hirsutism, osteomalacia). * **Levetiracetam:** This is also a first-line broad-spectrum AED. However, in many standardized clinical guidelines and recent NEET-PG patterns, Lamotrigine is frequently highlighted as the preferred initial monotherapy for generalized seizures. * **Ethosuximide:** This is the drug of choice for **Absence Seizures** only. It is ineffective against GTCS as it specifically targets T-type calcium channels in the thalamus. **High-Yield Clinical Pearls for NEET-PG:** * **Drug of Choice (DOC) for GTCS:** Valproate (Most effective, but avoid in pregnancy); Lamotrigine/Levetiracetam (Preferred alternatives). * **DOC for Absence Seizures:** Ethosuximide (Valproate if GTCS is also present). * **DOC for Myoclonic Seizures:** Valproate. * **Stevens-Johnson Syndrome (SJS):** A serious risk with Lamotrigine; always start with a low dose and titrate slowly.

Question 402: What is true regarding tolerance occurring in regular opium abusers?

A. Tolerance develops to all actions of morphine.
B. No tolerance occurs to euphoric and sedative actions of morphine.
C. No tolerance occurs to constipating and miotic actions of morphine. (Correct Answer)
D. The lethal dose of morphine is not significantly increased.

Explanation: In opioid pharmacology, **tolerance** refers to the need for increasing doses of a drug to achieve the same effect. However, tolerance does not develop uniformly across all organ systems. ### 1. Why Option C is Correct In chronic opium or morphine users, tolerance develops to most effects, but **miosis (pinpoint pupils)** and **constipation** are the two notable exceptions. * **Miosis:** Mediated by the Edinger-Westphal nucleus (mu and kappa receptors); this effect persists regardless of the duration of use. * **Constipation:** Opioids decrease intestinal motility and secretions via local enteric receptors. This effect remains constant, which is why chronic opioid users often require stimulant laxatives throughout their treatment. ### 2. Why Other Options are Incorrect * **Option A:** Tolerance is **differential**. It develops rapidly to euphoria, sedation, and respiratory depression, but not to miosis or constipation. * **Option B:** Tolerance develops **very rapidly** to the euphoric, sedative, and emetic (nausea/vomiting) actions. This is why addicts must continually escalate their dose to achieve a "high." * **Option C:** The lethal dose is **significantly increased** in addicts. A regular user can tolerate doses that would be fatal to a non-user due to the development of high-grade tolerance to respiratory depression. ### 3. NEET-PG High-Yield Pearls * **The "3 Cs" of Opioid Overdose:** Coma, Constriction of pupil (Miosis), and Cyanosis (Respiratory depression). * **Mnemonic for No Tolerance:** "**M**iosis and **C**onstipation" (Remember: **M**ore **C**onstipation). * **Exception to Miosis:** In severe overdose (hypoxia) or specific opioid use like **Meperidine (Pethidine)**, pupils may be dilated (mydriasis) rather than constricted. * **Withdrawal:** Opioid withdrawal is rarely life-threatening (unlike alcohol withdrawal) but is characterized by "everything running" (rhinorrhea, lacrimation, diarrhea, and mydriasis).

Question 403: Which agent is used to induce experimental Parkinson's disease in animals and humans?

A. MPTP
B. Methyl mercury
C. Rotenone
D. All of the above (Correct Answer)

Explanation: **Explanation:** To study Parkinson’s Disease (PD) and test potential therapies, researchers use neurotoxins that selectively damage dopaminergic neurons in the substantia nigra pars compacta, mimicking the pathology of PD. 1. **MPTP (1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine):** This is the most famous agent. It is a contaminant found in illicit meperidine synthesis. MPTP crosses the blood-brain barrier and is converted by **MAO-B** into **MPP+**, which is taken up by dopamine transporters. It inhibits mitochondrial complex I, leading to rapid, irreversible parkinsonism in humans and primates. 2. **Rotenone:** A commonly used pesticide and mitochondrial complex I inhibitor. Chronic systemic exposure in rodents reproduces the slow, progressive loss of dopaminergic neurons and the formation of **alpha-synuclein-positive cytoplasmic inclusions** (similar to Lewy bodies). 3. **Methyl mercury:** While primarily known for Minamata disease, chronic exposure to organic mercury is neurotoxic to the basal ganglia and can induce extrapyramidal symptoms and parkinsonian-like tremors in experimental models. **High-Yield Clinical Pearls for NEET-PG:** * **MPTP Mechanism:** MPTP $\rightarrow$ (via MAO-B) $\rightarrow$ MPP+ (Active toxin). * **Protective Agent:** **Selegiline** (MAO-B inhibitor) can prevent MPTP-induced toxicity by blocking the conversion to MPP+. * **Other Models:** **6-OHDA (6-hydroxydopamine)** is another classic agent used for lesioning the substantia nigra via direct intracranial injection. * **Paraquat:** A herbicide structurally similar to MPP+ that is also linked to increased PD risk.

Question 404: What is the drug of choice for malignant neuroleptic syndrome?

A. Danazol
B. Dantrolene (Correct Answer)
C. Propranolol
D. Diazepam

Explanation: **Explanation:** **Neuroleptic Malignant Syndrome (NMS)** is a life-threatening idiosyncratic reaction to antipsychotic drugs (dopamine antagonists). It is characterized by the clinical tetrad of **muscle rigidity ("lead-pipe" rigidity)**, hyperthermia, autonomic instability, and altered mental status. **Why Dantrolene is the Correct Answer:** The primary pathophysiology involves extreme muscle contraction leading to hyperthermia and rhabdomyolysis. **Dantrolene** is a direct-acting skeletal muscle relaxant. It works by binding to the **ryanodine receptor (RyR1)** on the sarcoplasmic reticulum, inhibiting the release of calcium ions into the cytosol. By preventing calcium-mediated excitation-contraction coupling, it effectively reduces muscle rigidity and heat production. **Analysis of Incorrect Options:** * **A. Danazol:** An attenuated androgen used primarily in the treatment of endometriosis and hereditary angioedema. It has no role in muscle relaxation or NMS. * **C. Propranolol:** A non-selective beta-blocker used for performance anxiety, essential tremors, and akathisia (a different extrapyramidal side effect), but it does not treat the core symptoms of NMS. * **D. Diazepam:** While benzodiazepines are used for sedation and mild muscle relaxation in NMS, they are supportive treatments and not the specific "drug of choice" for reversing the underlying rigidity. **High-Yield Clinical Pearls for NEET-PG:** * **Dantrolene** is also the drug of choice for **Malignant Hyperthermia** (triggered by volatile anesthetics/succinylcholine). * **Bromocriptine** (a dopamine agonist) is another specific treatment for NMS, used to overcome the dopamine blockade. * **Key Lab Finding:** Elevated **Creatine Kinase (CK)** levels due to intense muscle breakdown. * **Mnemonic for NMS Symptoms:** **FEVER** (Fever, Encephalopathy, Vital instability, Elevated CK, Rigidity).

Question 405: All of the following are side effects of ropinirole except?

A. Sedation
B. Nausea
C. Retroperitoneal Fibrosis (Correct Answer)
D. Hallucination

Explanation: **Explanation** The correct answer is **Retroperitoneal Fibrosis**. **1. Why Retroperitoneal Fibrosis is the correct answer:** Ropinirole is a **Non-Ergot** dopamine agonist. Retroperitoneal fibrosis, along with pleural and pericardial fibrosis, is a classic side effect associated specifically with **Ergot-derived** dopamine agonists (e.g., Bromocriptine, Cabergoline, Pergolide). These ergot derivatives act on 5-HT2B receptors, which triggers fibroblast proliferation. Since Ropinirole is a non-ergot derivative, it does not carry the risk of fibrotic complications. **2. Analysis of Incorrect Options:** * **Nausea:** This is the most common side effect of all dopamine agonists. It occurs due to the stimulation of dopamine receptors in the Area Postrema (Chemoreceptor Trigger Zone) outside the blood-brain barrier. * **Sedation:** Ropinirole can cause significant drowsiness and "sleep attacks" (sudden onset of sleep during daily activities), which is a high-yield side effect for competitive exams. * **Hallucinations:** By increasing dopaminergic activity in the mesolimbic pathway, ropinirole can cause psychiatric side effects, including vivid dreams, hallucinations, and confusion, especially in elderly patients. **3. NEET-PG High-Yield Pearls:** * **Classification:** Non-Ergot agonists include **Ropinirole** (D3 selective) and **Pramipexole** (D2 selective). * **Impulse Control Disorders:** Ropinirole is strongly associated with pathological gambling, hypersexuality, and compulsive shopping. * **Clinical Use:** Ropinirole is a first-line treatment for **Restless Leg Syndrome (RLS)** and is used as monotherapy in early Parkinson’s disease to delay the use of Levodopa. * **Apomorphine:** Another non-ergot agonist, used as "rescue therapy" for "off" episodes in Parkinson's, but causes severe vomiting (requires pre-treatment with Trimethobenzamide).

Question 406: Which of the following statements regarding Lithium is false?

A. Maximum plasma concentration is avoided due to a low therapeutic index.
B. It is contraindicated in pregnancy.
C. There is no individual variation in the rate of excretion. (Correct Answer)
D. 80% is reabsorbed in the proximal convoluted tubule.

Explanation: ### Explanation **1. Why Option C is the Correct (False) Statement:** Lithium excretion is almost entirely renal, and there is **significant individual variation** in its rate of excretion. The elimination half-life of Lithium varies widely (approximately 18–36 hours) depending on the patient’s age, renal function, and sodium balance. Because of this variability and its narrow therapeutic index, **Therapeutic Drug Monitoring (TDM)** is mandatory to tailor the dose for each individual. **2. Analysis of Other Options:** * **Option A (True):** Lithium has a very **low therapeutic index** (0.6–1.2 mEq/L). High peak plasma concentrations (Cmax) are avoided to prevent acute toxicity; hence, sustained-release formulations or divided doses are often used. * **Option B (True):** Lithium is generally contraindicated in pregnancy, especially during the first trimester, due to its teratogenic potential. It is associated with **Ebstein’s anomaly** (atrialization of the right ventricle). * **Option D (True):** Lithium is handled by the kidneys similarly to sodium. Approximately **80% of the filtered load is reabsorbed in the proximal convoluted tubule (PCT)**. This is clinically significant because conditions causing sodium depletion (e.g., diuretics, dehydration) lead to increased proximal reabsorption of Lithium, potentially causing toxicity. **3. High-Yield Clinical Pearls for NEET-PG:** * **Drug Interactions:** Thiazides, NSAIDs, and ACE inhibitors increase Lithium levels by decreasing its clearance. * **Side Effects:** L-I-T-H: **L**eukocytosis, **I**nsipidus (Nephrogenic Diabetes Insipidus), **T**remors/Teratogenicity, **H**ypothyroidism. * **Monitoring:** Check Serum Creatinine, TSH, and ECG before starting therapy. * **Drug of Choice:** Lithium remains the gold standard for the prophylaxis of Bipolar Affective Disorder (BPAD).

Question 407: Which drug is NOT used for analgesia in a patient with head injury?

A. Morphine (Correct Answer)
B. NSAIDs
C. Rofecoxib
D. Acetaminophen

Explanation: **Explanation:** The correct answer is **Morphine**. In patients with head injuries, opioids like Morphine are generally contraindicated or used with extreme caution due to three primary reasons: 1. **Respiratory Depression & ICP:** Morphine causes respiratory depression, leading to CO₂ retention (hypercapnia). CO₂ is a potent cerebral vasodilator, which increases cerebral blood flow and subsequently elevates **Intracranial Pressure (ICP)**, risking brain herniation. 2. **Pupillary Changes:** Morphine causes miosis (pinpoint pupils). This masks the pupillary pupillary dilation (mydriasis) that serves as a critical clinical sign of neurological deterioration or uncal herniation. 3. **Sedation:** It induces drowsiness and mental clouding, making it difficult for clinicians to perform accurate neurological assessments (GCS monitoring). **Why other options are incorrect:** * **NSAIDs (e.g., Ibuprofen) & Rofecoxib (COX-2 Inhibitor):** These provide effective analgesia without affecting the respiratory center or pupillary size. While non-selective NSAIDs are sometimes avoided acutely due to anti-platelet effects (risk of bleed), they do not carry the specific neurological contraindications of opioids. * **Acetaminophen (Paracetamol):** This is the drug of choice for mild-to-moderate pain in head injuries as it has no effect on ICP, respiration, or neurological monitoring. **High-Yield Clinical Pearls for NEET-PG:** * **DOC for Head Injury Pain:** Acetaminophen is preferred. * **Opioid of choice (if essential):** Fentanyl is sometimes preferred over Morphine in ICU settings due to its shorter half-life and less effect on histamine release, but the general rule for exams remains: **Avoid Morphine in Head Injury.** * **Other Contraindications for Morphine:** Bronchial asthma, Undiagnosed abdominal pain, Biliary colic, and Hypertrophy of the prostate.

Question 408: Thiopentone does not cause which of the following effects?

A. Fall in intracranial tension
B. Decreased oxygen consumption of brain
C. Decreased metabolic rate of brain
D. Decreased stage 2 of sleep (Correct Answer)

Explanation: **Explanation:** Thiopentone sodium is an ultra-short-acting barbiturate used for the induction of anesthesia. Understanding its effects on the CNS and sleep architecture is crucial for NEET-PG. **Why Option D is correct:** Barbiturates, including Thiopentone, significantly alter the sleep cycle. They **increase Stage 2 (NREM)** sleep while **decreasing Stage 3 and 4 (deep/slow-wave sleep)** and **decreasing REM sleep**. Therefore, the statement that it "decreases Stage 2" is incorrect, making it the right answer for this "except" type question. **Why other options are incorrect:** * **Options A, B, and C:** Thiopentone is a potent cerebral vasoconstrictor. It leads to a significant **reduction in Cerebral Blood Flow (CBF)**, **Cerebral Metabolic Rate of Oxygen (CMRO2)**, and **Intracranial Pressure (ICP)**. These properties make it a drug of choice for induction in patients with head injuries or space-occupying lesions (SOL) where intracranial tension is elevated. **High-Yield Clinical Pearls for NEET-PG:** * **Cerebral Protection:** Thiopentone provides "barbiturate coma" which protects the brain during focal ischemia by reducing metabolic demand. * **Respiratory Effect:** It is a potent respiratory depressant and can cause laryngospasm (ensure adequate depth or use of muscle relaxants). * **Cardiovascular Effect:** It causes peripheral vasodilation and can lead to hypotension; use with caution in hypovolemic patients. * **Contraindication:** Absolutely contraindicated in **Acute Intermittent Porphyria** (induces ALA synthetase). * **Redistribution:** The short duration of action is due to **redistribution** from the brain to skeletal muscle and fat, not due to rapid metabolism.

Question 409: Pancuronium differs from tubocurarine in which of the following aspects?

A. It is a depolarizing blocker.
B. Its action is not reversed by neostigmine.
C. It can cause a rise in blood pressure on rapid intravenous injection. (Correct Answer)
D. It causes marked histamine release.

Explanation: **Explanation:** The core difference between Pancuronium and d-Tubocurarine lies in their **autonomic side-effect profiles**. Both are non-depolarizing neuromuscular blockers, but they interact with different receptors outside the neuromuscular junction. **1. Why Option C is Correct:** Pancuronium possesses **vagolytic properties** (blocks muscarinic M2 receptors in the heart) and stimulates the release of norepinephrine from adrenergic nerve endings. This sympathomimetic effect leads to **tachycardia and a rise in blood pressure**, especially upon rapid intravenous injection. In contrast, d-Tubocurarine typically causes hypotension. **2. Why the Other Options are Incorrect:** * **Option A:** Both Pancuronium and d-Tubocurarine are **non-depolarizing (competitive)** blockers. Succinylcholine is the only clinically used depolarizing blocker. * **Option B:** The action of all non-depolarizing blockers, including Pancuronium, **can be reversed** by acetylcholinesterase inhibitors like **Neostigmine**, which increases the concentration of acetylcholine to outcompete the drug. * **Option D:** **d-Tubocurarine** is notorious for causing marked **histamine release**, leading to bronchospasm and hypotension. Pancuronium is preferred in clinical practice specifically because it causes little to no histamine release. **High-Yield Clinical Pearls for NEET-PG:** * **Pancuronium:** Long-acting; steroid-based; primarily excreted by kidneys (caution in renal failure). * **Mnemonic for d-Tubocurarine:** **H**istamine release, **H**ypotension, **H**epatic metabolism (minimal), and **H**ighly potent. * **Drug of Choice (DOC):** For patients with cardiovascular instability, **Vecuronium** or **Rocuronium** are preferred as they are cardiostable (lack the vagolytic effects of Pancuronium). * **Atracurium/Cisatracurium:** Preferred in renal/hepatic failure due to **Hofmann elimination**.

Question 410: Non-depolarizing neuromuscular blockade is potentiated by which of the following?

A. Hyperkalemia
B. Hypomagnesemia
C. Chronic phenytoin therapy
D. Quinidine (Correct Answer)

Explanation: **Explanation:** The potentiation of non-depolarizing neuromuscular blockers (NDNMBs) occurs through mechanisms that either decrease acetylcholine (ACh) release or stabilize the post-junctional membrane. **Why Quinidine is Correct:** **Quinidine** (a Class IA antiarrhythmic) potentiates NDNMBs by acting at both pre-junctional and post-junctional sites. It reduces the release of ACh from the motor nerve terminal and decreases the sensitivity of the motor end-plate to ACh. It also has a direct depressant effect on the muscle fiber itself. **Analysis of Incorrect Options:** * **Hyperkalemia (A):** High extracellular potassium causes partial depolarization of the resting membrane, making it easier for ACh to trigger an action potential. This **antagonizes** (reverses) the effect of NDNMBs. Conversely, **hypokalemia** potentiates the blockade. * **Hypomagnesemia (B):** Magnesium acts as a physiological calcium channel blocker at the nerve terminal. **Hypermagnesemia** inhibits ACh release and potentiates blockade. Therefore, hypomagnesemia would theoretically antagonize the block. * **Chronic Phenytoin Therapy (C):** Long-term use of phenytoin (and carbamazepine) leads to **resistance** to NDNMBs due to the up-regulation of acetylcholine receptors and increased metabolism of the blockers. (Note: Acute administration may potentiate the block, but chronic therapy antagonizes it). **High-Yield Clinical Pearls for NEET-PG:** * **Drugs that Potentiate NDNMBs:** Aminoglycosides (e.g., Gentamicin), Tetracyclines, Calcium channel blockers, Volatile anesthetics (Isoflurane > Halothane), and Lithium. * **Electrolyte Abnormalities that Potentiate NDNMBs:** Hypokalemia, Hypermagnesemia, Hypocalcemia, and Respiratory Acidosis. * **Myasthenia Gravis:** Patients are extremely sensitive to NDNMBs; even small doses can cause prolonged paralysis.

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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