Central Nervous System Pharmacology Practice Questions

Q: Which of the following antiepileptic drugs acts by opening potassium channels?

Ezogabine. **Explanation:** **Correct Answer: A. Ezogabine (Retigabine)** Ezogabine (known as Retigabine in Europe) has a unique mechanism of action among antiepileptics. It acts as a **positive allosteric modulator of KCNQ2-5 (Kv7.2–7.5) voltage-gated potassium channels**. By opening these channels, it facilitates an outward potassium current (the "M-current"), which stabilizes the resting membrane potential and hyperpolarizes the neuron, thereby reducing repetitive firing and neuronal excitability. **Analysis of Incorrect Options:** * **B. Felbamate:** Primarily acts by blocking **NMDA receptors** (glutamate) and modulating GABA-A receptors. It is reserved for refractory epilepsy due to risks of aplastic anemia and hepatic failure. * **C. Lacosamide:** Acts by enhancing the **slow inactivation of voltage-gated sodium channels**, unlike traditional sodium channel blockers (like Phenytoin) which affect fast inactivation. * **D. Gabapentin:** Despite its name, it does not act on GABA receptors. It binds to the **α2δ-1 subunit of voltage-gated calcium channels**, reducing the release of excitatory neurotransmitters. **High-Yield Facts for NEET-PG:** * **Ezogabine Side Effects:** A unique "blue-man" presentation—it can cause **blue skin discoloration** and **retinal pigmentation** (requires regular ophthalmological monitoring). * **Lacosamide:** Often tested for its "slow inactivation" mechanism and its lack of significant drug-drug interactions. * **Broad-spectrum vs. Narrow-spectrum:** Remember that drugs affecting potassium channels or multiple mechanisms (like Valproate/Topiramate) often have broad-spectrum activity.

Q: Ropinirole is most useful for the treatment of which condition?

Parkinson's disease. **Explanation:** **Ropinirole** is a non-ergoline **Dopamine Agonist** that acts selectively on D2 and D3 receptors. In **Parkinson’s disease**, there is a progressive loss of dopaminergic neurons in the substantia nigra. Ropinirole bypasses these degenerating neurons to directly stimulate postsynaptic dopamine receptors in the striatum, thereby improving motor symptoms like bradykinesia and rigidity. It is used both as monotherapy in early Parkinson's (to delay the use of Levodopa) and as an adjunct in advanced stages. **Analysis of Incorrect Options:** * **Wilson’s Disease:** This is a disorder of copper metabolism. Treatment involves copper chelators like **D-Penicillamine** or Trientine, and Zinc to prevent absorption. * **Hoffmann Syndrome:** This is a specific form of hypothyroid myopathy characterized by muscle stiffness and pseudohypertrophy. The treatment is **Thyroxine replacement**. * **Carpal Tunnel Syndrome:** This is a compression neuropathy of the median nerve. Management includes splinting, NSAIDs, corticosteroid injections, or surgical decompression. **High-Yield Clinical Pearls for NEET-PG:** * **Restless Leg Syndrome (RLS):** Ropinirole and Pramipexole are the first-line FDA-approved treatments for RLS. * **Side Effects:** A unique and high-yield side effect of dopamine agonists (Ropinirole/Pramipexole) is **impulse control disorders** (e.g., pathological gambling, hypersexuality) and **sudden sleep attacks**. * **Non-ergot vs. Ergot:** Unlike older ergot derivatives (Bromocriptine), Ropinirole does not cause cardiac valvular fibrosis or pleuropulmonary fibrosis.

Q: Which of the following statements is not true regarding the mechanism of action of benzodiazepines?

Has GABA mimetic action.. ### Explanation The mechanism of action of Benzodiazepines (BZDs) is a high-yield topic for NEET-PG. To understand why **Option D** is the correct answer (the false statement), we must distinguish between **GABA-facilitatory** and **GABA-mimetic** actions. **1. Why Option D is the correct answer (False statement):** Benzodiazepines are **GABA-facilitatory**, not GABA-mimetic. They require the presence of endogenous GABA to function. They bind to an allosteric site on the GABA-A receptor and increase the **frequency** of chloride channel opening. In contrast, **Barbiturates** at high doses can act as GABA-mimetics (directly opening the channel even in the absence of GABA), which is why they have a lower safety margin and can cause profound CNS depression compared to BZDs. **2. Analysis of Incorrect Options (True statements):** * **Option A:** BZDs act on multiple levels of the neuraxis. Their sedative-hypnotic effects are mediated via the **ascending reticular formation**, while their anxiolytic effects are primarily due to action on the **limbic system**. * **Option B:** BZDs bind specifically to the alpha-gamma interface of the **GABA-A receptor** (a pentameric ligand-gated chloride channel). * **Option C:** By increasing the frequency of channel opening, BZDs increase **Chloride (Cl-) conductance**, leading to neuronal hyperpolarization and inhibition. ### High-Yield Clinical Pearls for NEET-PG: * **BZD Antagonist:** **Flumazenil** (competitive antagonist at the BZD site). * **Receptor Subtypes:** $\alpha_1$ subunits mediate sedation/hypnosis; $\alpha_2$ and $\alpha_3$ subunits mediate anxiolytic and muscle relaxant effects. * **Safety:** BZDs exhibit a "ceiling effect" because they depend on endogenous GABA, making them safer than barbiturates in overdose. * **Mnemonic:** Benzodiazepines increase **Fr**equency (**Fr**enzodiazepines); Barbiturates increase **Du**ration (**Barbi-durat-es**).

Q: Which sedative agent facilitates GABAergic action but lacks anticonvulsant and muscle relaxant properties, and does not affect sleep?

Zolpidem. ### Explanation **Correct Answer: B. Zolpidem** **Mechanism and Rationale:** Zolpidem is a non-benzodiazepine sedative-hypnotic (Z-drug). While it facilitates GABAergic action like benzodiazepines, it is highly selective for the **$\alpha_1$ subunit** of the $GABA_A$ receptor [1]. * The **$\alpha_1$ subunit** mediates sedation and amnesia. * The **$\alpha_2, \alpha_3,$ and $\alpha_5$ subunits** are responsible for anxiolytic, muscle relaxant, and anticonvulsant effects. Because Zolpidem lacks significant affinity for these other subunits, it provides pure sedation without the muscle relaxant or anticonvulsant properties associated with traditional benzodiazepines [1]. Furthermore, it has minimal impact on sleep architecture (it does not significantly suppress REM or N3 sleep stages), making it ideal for treating insomnia [2]. **Analysis of Incorrect Options:** * **A. Diazepam:** A classic benzodiazepine that binds non-selectively to $\alpha_1, \alpha_2, \alpha_3,$ and $\alpha_5$ subunits. Consequently, it possesses potent anticonvulsant, muscle relaxant, and anxiolytic properties. * **C. Phenobarbitone:** A barbiturate that increases the *duration* of GABA channel opening. It is a powerful anticonvulsant and significantly alters sleep architecture (decreases REM sleep) [2]. * **D. Buspirone:** An anxiolytic that acts as a **5-$HT_{1A}$ partial agonist**. It does not facilitate GABAergic action and lacks sedative, anticonvulsant, or muscle relaxant properties. **High-Yield NEET-PG Pearls:** * **Z-drugs (Zolpidem, Zaleplon, Eszopiclone):** Preferred for insomnia due to low potential for tolerance, dependence, and "hangover" effects. * **Antidote:** Flumazenil reverses the effects of both Benzodiazepines and Z-drugs. * **Zaleplon:** Has the shortest half-life among Z-drugs, useful for sleep-onset insomnia. * **Eszopiclone:** Often used for long-term management of insomnia.

Q: A young man with a known history of heroin addiction is brought to the emergency department in an unconscious state. On examination, the patient presents with decreased bowel sounds, depressed respiration, and pinpoint pupils. What is the treatment of choice for this patient?

Intravenous naloxone. ### Explanation **Correct Answer: B. Intravenous naloxone** **Mechanism and Rationale:** The patient presents with the classic **"Opioid Overdose Triad"**: Coma (unconscious), Respiratory Depression, and Miosis (pinpoint pupils). Decreased bowel sounds further confirm opioid-induced slowing of gastrointestinal motility. In an acute emergency, the priority is to reverse respiratory depression. **Naloxone** is a competitive opioid antagonist with a high affinity for $\mu$-receptors. It is the treatment of choice because it acts rapidly (within 1–2 minutes when given IV) to displace the heroin from the receptors and restore spontaneous breathing. **Why other options are incorrect:** * **A. Oral naltrexone:** While naltrexone is an opioid antagonist, it has a long duration of action and is used for **relapse prevention** (maintenance therapy) in detoxified patients. It is not used in emergencies due to its slow onset and oral administration. * **C. Oral diazepam:** Diazepam is a benzodiazepine and a CNS depressant. Administering it to a patient with respiratory depression would worsen the condition and potentially be fatal. * **D. Oral buprenorphine:** This is a partial $\mu$-agonist used for opioid substitution therapy. In an acute overdose, adding a partial agonist will not provide the rapid reversal required and may even complicate the clinical picture. **High-Yield Clinical Pearls for NEET-PG:** * **Short Half-life:** Naloxone has a shorter half-life (approx. 30–60 mins) than most opioids (like heroin or methadone). Therefore, **repeated dosing** or an IV infusion may be necessary to prevent the patient from slipping back into a coma once the naloxone wears off. * **Diagnostic Use:** Naloxone is often used as a diagnostic tool in "coma of unknown origin." * **Withdrawal:** Rapid administration in an addict can precipitate **acute withdrawal syndrome** (agitation, vomiting, lacrimation, rhinorrhea).

Q: A patient on Phenytoin therapy develops depression, for which he was prescribed tricyclic antidepressants. He now complains of lassitude and his Hb reading is 8 gm/dl. What is the next step in the management of this patient?

Estimate MCV. ### Explanation **1. Why "Estimate MCV" is the correct answer:** The patient is presenting with symptoms of anemia (lassitude, Hb 8 gm/dl) while on long-term **Phenytoin** therapy. Phenytoin is a well-known inducer of **folate deficiency**, which leads to **Megaloblastic Anemia**. The mechanism involves Phenytoin interfering with intestinal folate absorption and increasing its metabolism. In megaloblastic anemia, the Mean Corpuscular Volume (MCV) is elevated (>100 fL). Therefore, estimating the MCV is the most appropriate next step to confirm the presence of macrocytosis before initiating folic acid supplementation. *Note:* Tricyclic antidepressants (TCAs) are mentioned as a distractor, though they can occasionally lower the seizure threshold, they are not the primary cause of the hematological findings here. **2. Why other options are incorrect:** * **Chest X-ray:** While Phenytoin can rarely cause interstitial lung disease, it does not explain the low hemoglobin and lassitude. * **Estimate GGT:** Gamma-glutamyl transferase (GGT) is a marker of enzyme induction or liver pathology. While Phenytoin is a potent hepatic enzyme inducer and can raise GGT levels, this test does not help diagnose the cause of the patient's anemia. **3. Clinical Pearls for NEET-PG:** * **Phenytoin Side Effects (Mnemonic: HOT MALAI):** **H**irsutism, **O**steomalacia, **T**eratogenicity (Fetal Hydantoin Syndrome), **M**egaloblastic anemia, **A**taxia, **L**ymphadenopathy, **A**rrythmias (on rapid IV), **I**nsulin inhibition (Hyperglycemia), and **Gingival Hyperplasia**. * **Folate Supplementation:** Giving folic acid to a patient on Phenytoin can actually *decrease* the serum levels of Phenytoin (by increasing its metabolism), potentially leading to breakthrough seizures. * **Zero-Order Kinetics:** Phenytoin follows saturation kinetics; small dose increases can lead to toxic levels.

Q: All of the following decrease skeletal muscle tone by CNS effects, except:

D-tubocurarin. Skeletal muscle relaxants are broadly classified into two categories based on their site of action: **Centrally acting muscle relaxants** and **Peripherally acting muscle relaxants**. ### **Explanation of the Correct Answer** **A. D-tubocurarine:** This is a **peripherally acting** neuromuscular blocker. It acts at the **Neuromuscular Junction (NMJ)** by competitively antagonizing nicotinic acetylcholine receptors ($N_m$) on the motor endplate. It does not cross the blood-brain barrier and, therefore, has **no CNS effects**. This makes it the "except" in the list. ### **Explanation of Incorrect Options** * **B. Diazepam:** A Benzodiazepine that acts centrally by enhancing **GABA-A** mediated presynaptic inhibition in the spinal cord. It is used for both muscle spasms and spasticity. * **C. Baclofen:** A centrally acting agent that is a selective **GABA-B agonist**. It acts primarily at the spinal level to reduce excitatory neurotransmitter release, effectively reducing spasticity in conditions like Multiple Sclerosis. * **D. Mephenesin:** The prototype of centrally acting muscle relaxants. It acts on the **internuncial neurons** of the spinal cord to reduce skeletal muscle tone without affecting consciousness. ### **High-Yield Clinical Pearls for NEET-PG** * **Dantrolene:** The only peripherally acting muscle relaxant that acts **directly on the muscle** (by inhibiting Calcium release from the Sarcoplasmic Reticulum via RyR1 receptors). It is the drug of choice for **Malignant Hyperthermia**. * **Tizanidine:** A centrally acting muscle relaxant that works as an **$\alpha_2$ adrenergic agonist** (similar to clonidine but with less hypotensive effect). * **Site Summary:** * CNS: Diazepam, Baclofen, Tizanidine. * NMJ: D-tubocurarine, Succinylcholine. * Muscle: Dantrolene.

Q: Which benzodiazepine does not have significant anticonvulsant properties?

Temazepam. **Explanation:** Benzodiazepines (BZDs) act by potentiating GABA-mediated inhibitory neurotransmission. While most BZDs share common properties (anxiolytic, sedative-hypnotic, muscle relaxant, and anticonvulsant), their clinical utility is determined by their specific receptor affinity and pharmacokinetic profile. **Why Temazepam is the correct answer:** Temazepam is a **short-to-intermediate acting BZD** primarily used as a **hypnotic** for the treatment of insomnia. It lacks significant anticonvulsant or muscle relaxant properties at standard therapeutic doses. Its pharmacological profile is optimized for inducing and maintaining sleep without the prolonged CNS depression required for seizure suppression. **Analysis of Incorrect Options:** * **Nitrazepam:** Primarily used as a hypnotic, but it possesses potent anticonvulsant properties and is clinically used in the management of infantile spasms (West Syndrome) and certain myoclonic seizures. * **Diazepam:** A prototype long-acting BZD. It is a first-line agent for terminating acute seizures and **Status Epilepticus** due to its high lipid solubility and rapid brain entry. * **Clonazepam:** A highly potent BZD specifically used as a long-term **antiepileptic drug**. It is the drug of choice for Absence seizures (as an alternative to Ethosuximide) and Myoclonic seizures. **NEET-PG High-Yield Pearls:** * **Status Epilepticus:** Lorazepam is often preferred over Diazepam due to its longer duration of action in the brain (less redistribution). * **Metabolism:** Temazepam, Oxazepam, and Lorazepam (**T-O-L**) undergo direct glucuronidation (Phase II) and do not form active metabolites, making them safer in elderly patients and those with liver failure. * **Antidote:** Flumazenil is the specific competitive antagonist for BZD overdose.

Q: Which of the following statements about vigabatrin is true?

Visual disturbances can occur. **Vigabatrin** is a structural analog of GABA that acts as an **irreversible inhibitor of GABA transaminase (GABA-T)**, the enzyme responsible for the degradation of GABA. By inhibiting this enzyme, it significantly increases the concentration of GABA (an inhibitory neurotransmitter) in the synaptic cleft. ### Why the correct answer is right: **Option D: Visual disturbances can occur.** The most significant and characteristic adverse effect of vigabatrin is **permanent bilateral concentric visual field constriction** (peripheral vision loss), occurring in up to 30-50% of patients. This is due to retinal toxicity. Because of this risk, it is usually reserved for refractory cases, and regular ophthalmological monitoring (perimetry) is mandatory. ### Why the other options are wrong: * **Option A:** Vigabatrin inhibits the *metabolism* of GABA, not its reuptake. **Tiagabine** is the drug that blocks neuronal and glial reuptake of GABA by inhibiting the GAT-1 transporter. * **Option B:** Vigabatrin is not used for absence seizures; in fact, it may **exacerbate** absence and myoclonic seizures. It is primarily used for refractory focal seizures and is the **drug of choice for Infantile Spasms (West Syndrome)** associated with Tuberous Sclerosis. * **Option C:** Life-threatening skin disorders (like Stevens-Johnson Syndrome) are more commonly associated with **Lamotrigine, Phenytoin, or Carbamazepine**, rather than Vigabatrin. ### High-Yield NEET-PG Pearls: * **Mechanism:** Irreversible "Suicide" inhibition of GABA-T. * **DOC:** Infantile Spasms (West Syndrome) in Tuberous Sclerosis. * **Black Box Warning:** Permanent vision loss (Vigabatrin Risk Evaluation and Mitigation Strategy - REMS program). * **Mnemonic:** **Vi**gabratrin **G**ABA **T**ransaminase inhibitor → **Vi**sual field defects.

Question 1

Which of the following antiepileptic drugs acts by opening potassium channels?

Accepted Answer

Ezogabine

Answer

Felbamate

Answer

Lacosamide

Answer

Gabapentin

Question 2

Ropinirole is most useful for the treatment of which condition?

Accepted Answer

Parkinson's disease

Answer

Wilson's disease

Answer

Hoffmann syndrome

Answer

Carpal tunnel syndrome

Question 3

Which of the following statements is not true regarding the mechanism of action of benzodiazepines?

Accepted Answer

Has GABA mimetic action.

Answer

Acts on the midbrain, ascending reticular formation, and limbic system.

Answer

Exerts effects through the GABA A receptors.

Answer

Increases the conductance of Cl- channels.

Question 4

Which sedative agent facilitates GABAergic action but lacks anticonvulsant and muscle relaxant properties, and does not affect sleep?

Accepted Answer

Zolpidem

Answer

Diazepam

Answer

Phenobarbitone

Answer

Buspirone

Question 5

A young man with a known history of heroin addiction is brought to the emergency department in an unconscious state. On examination, the patient presents with decreased bowel sounds, depressed respiration, and pinpoint pupils. What is the treatment of choice for this patient?

Accepted Answer

Intravenous naloxone

Answer

Oral naltrexone

Answer

Oral diazepam

Answer

Oral buprenorphine

Question 6

A patient on Phenytoin therapy develops depression, for which he was prescribed tricyclic antidepressants. He now complains of lassitude and his Hb reading is 8 gm/dl. What is the next step in the management of this patient?

Accepted Answer

Estimate MCV

Answer

Chest X-ray

Answer

Estimate GGT

Answer

None of the above

Question 7

All of the following decrease skeletal muscle tone by CNS effects, except:

Accepted Answer

D-tubocurarin

Answer

Diazepam

Answer

Baclofen

Answer

Mephenesin

Question 8

All of the following are surface anesthetics except:

Accepted Answer

Bupivacaine

Answer

Lignocaine

Answer

Procaine

Answer

Cinchocaine

Question 9

Which benzodiazepine does not have significant anticonvulsant properties?

Accepted Answer

Temazepam

Answer

Nitrazepam

Answer

Diazepam

Answer

Clonazepam

Question 10

Which of the following statements about vigabatrin is true?

Accepted Answer

Visual disturbances can occur

Answer

Blocks neuronal reuptake of GABA

Answer

Drug of choice in absence seizures

Answer

Life-threatening skin disorders may occur

Central Nervous System Pharmacology — MCQs

Central Nervous System Pharmacology — MCQs

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