Central Nervous System Pharmacology Practice Questions

Q: Which of the following is NOT a pharmacological effect of benzodiazepines?

Retrograde amnesia. **Explanation:** Benzodiazepines (BZDs) act by enhancing the effect of the inhibitory neurotransmitter GABA at the **GABA-A receptor**. By increasing the frequency of chloride channel opening, they cause hyperpolarization of neurons, leading to various CNS effects. **Why "Retrograde Amnesia" is the correct answer:** Benzodiazepines cause **Anterograde amnesia** (inability to form new memories after taking the drug), which is clinically useful for unpleasant medical procedures like endoscopies. They **do not** cause **Retrograde amnesia** (loss of memories formed before the drug administration). This is a common "trap" question in competitive exams. **Analysis of Incorrect Options:** * **A. Anxiolysis:** At low doses, BZDs selectively inhibit circuits in the limbic system, making them effective for treating generalized anxiety and panic disorders. * **B. Sedation:** BZDs exert a calming effect and induce sleep (hypnosis) by depressing the CNS, though they reduce REM sleep duration. * **D. Anticonvulsant action:** By enhancing GABAergic inhibition, BZDs suppress the spread of seizure activity. Drugs like Diazepam and Lorazepam are first-line for Status Epilepticus. **High-Yield Clinical Pearls for NEET-PG:** * **Mechanism:** BZDs increase the **frequency** of chloride channel opening (Barbiturates increase the **duration**). * **Antidote:** **Flumazenil** is a competitive BZD antagonist used for overdose. * **Metabolism:** Most BZDs are metabolized by the liver. **LOT** (Lorazepam, Oxazepam, Temazepam) are preferred in elderly patients or those with liver failure as they undergo direct conjugation. * **Muscle Relaxation:** BZDs also provide central muscle relaxation via action on the spinal cord.

Q: All of the following drugs can be used for the prophylaxis of migraine except?

Sumatriptan. **Explanation:** The management of migraine is divided into two categories: **Abortive (Acute) treatment** and **Prophylactic (Preventive) treatment**. **Why Sumatriptan is the correct answer:** Sumatriptan is a selective **5-HT$_{1B/1D}$ receptor agonist**. Its primary mechanism involves vasoconstriction of dilated cranial blood vessels and inhibition of neuropeptide release 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. It has no role in prophylaxis and, if overused, can actually lead to "Medication Overuse Headache." **Analysis of Incorrect Options (Prophylactic Agents):** * **Propranolol (Option A):** A non-selective beta-blocker and the **first-line drug** for migraine prophylaxis. It works by stabilizing vascular tone and increasing the threshold for migraine triggers. * **Amitriptyline (Option C):** A Tricyclic Antidepressant (TCA) that is highly effective for prophylaxis, especially in patients with co-existing tension-type headaches, depression, or insomnia. * **Flunarizine (Option D):** A non-selective **Calcium Channel Blocker** (CCB) with H1-blocking activity. It is specifically used for prophylaxis due to its long half-life, though it may cause weight gain and sedation. **High-Yield NEET-PG Pearls:** 1. **DOC for Acute Attack:** Mild (NSAIDs/Paracetamol); Moderate-Severe (Triptans). 2. **DOC for Prophylaxis:** Propranolol (most common) or Amitriptyline. 3. **Valproate and Topiramate** are the preferred anti-epileptics for migraine prevention. 4. **CGRP Antagonists (Erenumab):** Newer monoclonal antibodies used for refractory prophylaxis. 5. **Contraindication for Triptans:** Ischemic heart disease or Prinzmetal angina (due to coronary vasospasm).

Q: Which of the following is a gender-specific adverse effect of valproate?

Polycystic ovarian disease. **Explanation:** **Sodium Valproate** is a broad-spectrum antiepileptic drug that acts by increasing GABA levels, inhibiting sodium channels, and blocking T-type calcium channels. **Why Polycystic Ovarian Disease (PCOD) is the correct answer:** Valproate is strongly associated with endocrine disruptions in females. It can cause **hyperandrogenism** and interfere with the hypothalamic-pituitary-ovarian axis, leading to menstrual irregularities, hirsutism, and the development of **Polycystic Ovarian Disease (PCOD)**. This is a gender-specific adverse effect as it specifically impacts the female reproductive system. Due to this risk, along with its high teratogenic potential (neural tube defects), valproate is generally avoided in women of childbearing age unless no other alternative exists. **Analysis of Incorrect Options:** * **A. Weight gain:** This is a very common side effect of valproate, but it occurs in both males and females (not gender-specific). * **B. Tremors:** Fine tremors are a dose-related side effect seen in a significant percentage of patients regardless of gender. * **C. Alopecia:** Transient hair loss or thinning (often resulting in "curly hair" regrowth) is a known side effect but affects both sexes. **High-Yield NEET-PG Pearls:** * **Teratogenicity:** Valproate is the most teratogenic antiepileptic, specifically causing **Spina Bifida** (Neural tube defects). * **Mnemonic for Valproate Side Effects (VALPROATE):** **V**omiting, **A**lopecia, **L**iver toxicity (Hepatotoxicity - most serious), **P**ancreatitis/PCOD, **R**etention of weight (Weight gain), **O**edema, **A**norexia, **T**remors/Teratogenicity, **E**nzyme inhibitor (Note: It is a potent microsomal enzyme inhibitor, unlike most other AEDs which are inducers).

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

Morphine. **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.

Q: Thiopentone does not cause which of the following effects?

Decreased stage 2 of sleep. **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.

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

Quinidine. **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.

Q: Ketamine acts on which receptors?

NMDA. **Explanation:** **Ketamine** is a unique intravenous anesthetic agent that primarily acts as a non-competitive antagonist at the **NMDA (N-methyl-D-aspartate) receptors**. These receptors are a subtype of glutamate receptors located in the brain and spinal cord. By blocking these receptors, ketamine inhibits the excitatory neurotransmitter glutamate, leading to a state of **"Dissociative Anesthesia."** This state is characterized by profound analgesia, amnesia, and a cataleptic appearance where the patient’s eyes remain open with a slow nystagmic gaze, yet they are disconnected from their surroundings. **Analysis of Incorrect Options:** * **GABA (Option A):** Most intravenous anesthetics (like Propofol, Etomidate, and Thiopental) and Benzodiazepines act by enhancing GABA-A receptors. Ketamine is a notable exception as it does not primarily act on the GABA system. * **Muscarinic (Option B):** Ketamine actually possesses mild anticholinergic properties (which can lead to bronchodilation), but this is not its primary mechanism for anesthesia. * **5-HT4 (Option C):** These are serotonin receptors primarily involved in gastrointestinal motility and have no role in the anesthetic action of Ketamine. **High-Yield Clinical Pearls for NEET-PG:** 1. **Sympathomimetic Action:** Unlike other induction agents, Ketamine increases HR, BP, and CO, making it the **induction agent of choice for patients in hypovolemic shock.** 2. **Bronchodilation:** It is the drug of choice for induction in **asthmatic patients.** 3. **Emergence Delirium:** A common side effect characterized by hallucinations and vivid dreams; it can be prevented by co-administration of **Benzodiazepines (Midazolam).** 4. **Contraindications:** Avoid in patients with increased Intracranial Pressure (ICP) or Intraocular Pressure (IOP), and in those with Ischemic Heart Disease (due to increased myocardial oxygen demand).

Question 1

Which of the following is NOT a pharmacological effect of benzodiazepines?

Accepted Answer

Retrograde amnesia

Answer

Anxiolysis

Answer

Sedation

Answer

Anticonvulsant action

Question 2

All of the following drugs can be used for the prophylaxis of migraine except?

Accepted Answer

Sumatriptan

Answer

Propranolol

Answer

Amitriptyline

Answer

Flunarizine

Question 3

Which of the following is a gender-specific adverse effect of valproate?

Accepted Answer

Polycystic ovarian disease

Answer

Weight gain

Answer

Tremors

Answer

Alopecia

Question 4

All of the following are true about cocaine except one?

Accepted Answer

Produces para-aminobenzoic acid as a metabolite

Answer

Is an ester of benzoic acid

Answer

Is metabolized by the liver

Answer

Is a vasoconstrictor

Question 5

What is true regarding tolerance occurring in regular opium abusers?

Accepted Answer

No tolerance occurs to constipating and miotic actions of morphine.

Answer

Tolerance develops to all actions of morphine.

Answer

No tolerance occurs to euphoric and sedative actions of morphine.

Answer

The lethal dose of morphine is not significantly increased.

Question 6

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

Accepted Answer

Morphine

Answer

NSAIDs

Answer

Rofecoxib

Answer

Acetaminophen

Question 7

Thiopentone does not cause which of the following effects?

Accepted Answer

Decreased stage 2 of sleep

Answer

Fall in intracranial tension

Answer

Decreased oxygen consumption of brain

Answer

Decreased metabolic rate of brain

Question 8

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

Accepted Answer

Quinidine

Answer

Hyperkalemia

Answer

Hypomagnesemia

Answer

Chronic phenytoin therapy

Question 9

Ketamine acts on which receptors?

Accepted Answer

NMDA

Answer

GABA

Answer

Muscarinic

Answer

5-HT4

Question 10

Which of the following factors markedly increases the risk of valproate-induced liver toxicity?

Accepted Answer

Age younger than 2 years

Answer

Allergic reactions to phenobarbital

Answer

Male gender

Answer

Family history of epilepsy

Central Nervous System Pharmacology — MCQs

Central Nervous System Pharmacology — MCQs

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