Central Nervous System Pharmacology Practice Questions

Q: Which of the following is a 5-HT2A antagonist drug?

Ketanserin. **Explanation:** **Ketanserin** is a selective **5-HT2A receptor antagonist** that also possesses $\alpha_1$-adrenergic blocking properties. Its primary pharmacological action involves blocking 5-HT2A receptors on smooth muscles (causing vasodilation) and platelets (inhibiting aggregation). Clinically, it has been used as an antihypertensive agent and in the management of Raynaud’s phenomenon and carcinoid syndrome. **Analysis of Incorrect Options:** * **Clozapine (Option A):** While Clozapine is an atypical antipsychotic that has high affinity for 5-HT2A receptors, it is primarily classified as a **D2/5-HT2A antagonist**. However, in the context of pure pharmacological classification for competitive exams, Ketanserin is the "prototype" 5-HT2A antagonist. * **Cisapride (Option B):** This is a **5-HT4 agonist**. It was used as a prokinetic agent to increase lower esophageal sphincter tone and accelerate gastric emptying, though its use is now restricted due to the risk of QT prolongation (Torsades de Pointes). * **Sumatriptan (Option C):** This is a selective **5-HT1B/1D agonist**. It is the gold standard for the acute treatment of migraine, acting via vasoconstriction of cranial vessels and inhibition of neuropeptide release. **High-Yield Clinical Pearls for NEET-PG:** * **Ritanserin** is another specific 5-HT2A antagonist often mentioned alongside Ketanserin. * **Cyproheptadine** is a non-selective 5-HT2 antagonist (also blocks H1) used in **Serotonin Syndrome**. * **5-HT3 Antagonists** (e.g., Ondansetron) are the only 5-HT receptors that are **ionotropic** (ligand-gated ion channels); all others are G-protein coupled receptors (GPCRs).

Q: Which drug is used in absence seizures and has a narrow spectrum of antiepileptic activity?

Ethosuximide. **Explanation** **Ethosuximide** is the drug of choice for **absence seizures (petit mal)** in children. Its mechanism of action involves the selective inhibition of **T-type Ca²⁺ channels** in thalamic neurons, which are responsible for the characteristic 3-Hz spike-and-wave discharges seen on EEG in absence epilepsy. It is considered a **narrow-spectrum** agent because it is ineffective against generalized tonic-clonic seizures (GTCS) or focal seizures. **Analysis of Incorrect Options:** * **Sodium Valproate:** While it is also a drug of choice for absence seizures, it is a **broad-spectrum** antiepileptic. It is preferred over ethosuximide only if the patient has concomitant GTCS. * **Lamotrigine:** This is a broad-spectrum agent used for various seizures, including absence seizures (as an alternative). However, it is not the primary narrow-spectrum drug for this indication. * **Primidone:** A barbiturate derivative primarily used for focal and generalized tonic-clonic seizures. It is not used for absence seizures and can sometimes exacerbate them. **High-Yield NEET-PG Pearls:** * **Drug of Choice (DOC):** Ethosuximide is the DOC for pure absence seizures. If absence seizures coexist with GTCS, **Valproate** becomes the DOC. * **Side Effects of Ethosuximide:** Remember the mnemonic **EFGHIJ** – **E**thosuximide causes **F**atigue, **G**I distress, **H**eadache, **I**tching (Urticaria), and Stevens-**J**ohnson syndrome. * **EEG Finding:** Absence seizures are classically associated with **3-Hz spike-and-wave** patterns. * **Contraindication:** Avoid **Carbamazepine** and **Phenytoin** in absence seizures as they may worsen the condition.

Q: Which of the following agents does not act via GABAA-Cl– channel complex receptors?

Promethazine. **Explanation:** The **GABA-A receptor** is a ligand-gated ion channel (ionotropic receptor) that, when activated, increases chloride conductance, leading to neuronal hyperpolarization and CNS depression. **Why Promethazine is the Correct Answer:** Promethazine is a **first-generation H1-antihistamine** with significant anticholinergic and alpha-blocking properties. It does not interact with the GABA-A receptor complex. Its sedative effects are primarily due to the blockade of central H1 receptors and muscarinic receptors in the brain. **Analysis of Incorrect Options:** * **Benzodiazepines (B):** These are positive allosteric modulators that bind to a specific site on the GABA-A receptor, increasing the **frequency** of chloride channel opening. * **Thiopentone (C):** As a barbiturate, it binds to a distinct site on the GABA-A receptor to increase the **duration** of chloride channel opening. At high doses, it can also act as a GABA-mimetic. * **Zopiclone (A):** This is a "Z-drug" (non-benzodiazepine hypnotic). Despite having a different chemical structure than benzodiazepines, it binds specifically to the **alpha-1 subunit** of the GABA-A receptor to exert its hypnotic effect. **NEET-PG High-Yield Pearls:** * **GABA-A vs. GABA-B:** GABA-A is ionotropic (Chloride channel); GABA-B is metabotropic (G-protein coupled, linked to K+ channels). **Baclofen** is a GABA-B agonist. * **Flumazenil:** A competitive antagonist that reverses the effects of Benzodiazepines and Z-drugs, but **not** Barbiturates. * **Promethazine Clinical Use:** Often used for motion sickness and as a pre-anesthetic medication due to its antiemetic and sedative properties.

Q: What is the drug of choice for status epilepticus?

Lorazepam. **Explanation:** **Status Epilepticus (SE)** is a medical emergency defined as a continuous seizure lasting more than 5 minutes or recurrent seizures without recovery of consciousness between episodes. **Why Lorazepam is the Correct Answer:** Benzodiazepines (BZDs) are the first-line agents for terminating acute seizures because they enhance GABA-A mediated inhibition. **Lorazepam (IV)** is the preferred drug of choice (DOC) over Diazepam because it is less lipid-soluble. This allows it to remain in the brain for a longer duration (high redistribution half-life), providing a more sustained anticonvulsant effect (up to 12–24 hours) compared to Diazepam, which redistributes rapidly into fat stores, leading to a shorter duration of action. **Analysis of Incorrect Options:** * **Valproate (A):** While IV Valproate is an effective second-line agent for SE (especially if BZDs fail), it is not the initial drug of choice. * **Phenytoin (B):** Phenytoin (or Fosphenytoin) is used as a second-line agent to prevent the *recurrence* of seizures after the acute episode has been terminated by a BZD. It has a slow onset of action and cannot be used for immediate termination. * **Carbamazepine (D):** This is the DOC for Focal (Partial) seizures and Trigeminal Neuralgia. It is not used in SE and can actually worsen certain generalized seizures (like absence or myoclonic seizures). **High-Yield Clinical Pearls for NEET-PG:** * **Order of Management:** 1st line: Lorazepam (IV); 2nd line: Fosphenytoin, Valproate, or Levetiracetam; 3rd line (Refractory SE): Midazolam infusion, Propofol, or Thiopental. * **Route:** If IV access is unavailable, **Intramuscular (IM) Midazolam** is the preferred alternative. * **Fosphenytoin vs. Phenytoin:** Fosphenytoin is a prodrug; it is preferred over Phenytoin because it is water-soluble, causes less local irritation (Purple Glove Syndrome), and can be infused faster.

Q: Lignocaine can be used in all of the following conditions except?

Convulsions. **Explanation:** The correct answer is **Convulsions**. Lignocaine (Lidocaine) is a Class Ib anti-arrhythmic and a versatile local anesthetic; however, it is contraindicated in the treatment of convulsions because it is itself a potent **pro-convulsant** at high plasma concentrations. **1. Why Convulsions is the correct answer:** Lignocaine toxicity follows a predictable pattern of Central Nervous System (CNS) effects. While it initially causes circumoral numbness and tinnitus, higher doses lead to excitatory effects, including **generalized tonic-clonic seizures**. This occurs because lignocaine selectively inhibits inhibitory cortical pathways, leading to unopposed excitatory activity. Therefore, it is never used to treat seizures; instead, benzodiazepines (like Midazolam) or Intralipid emulsion are used to treat lignocaine-induced convulsions. **2. Analysis of Incorrect Options:** * **Ventricular Fibrillation:** Lignocaine is a Class Ib anti-arrhythmic that blocks activated and inactivated sodium channels. It is indicated in the ACLS protocol for pulseless VT/VF (though Amiodarone is often preferred). * **Spinal Anesthesia:** Lignocaine (5% heavy) was historically used for spinal anesthesia due to its rapid onset. However, its use has decreased due to the risk of **Transient Neurological Symptoms (TNS)**. * **Epidural Anesthesia:** Lignocaine (1.5%–2%) is frequently used for epidural anesthesia when a rapid onset of sensory and motor block is required (e.g., emergency Cesarean section). **Clinical Pearls for NEET-PG:** * **Maximum Dose:** 4 mg/kg (plain) and 7 mg/kg (with Adrenaline). * **Metabolism:** Primarily in the liver by CYP450 enzymes. * **Drug of Choice:** Lignocaine is the drug of choice for **ventricular arrhythmias** occurring post-Myocardial Infarction. * **Toxicity Sign:** The earliest sign of systemic toxicity (LAST) is often **perioral numbness** or a metallic taste.

Q: What is the side effect of phenytoin when its plasma concentration is above the therapeutic level?

Ataxia. Phenytoin is a commonly tested antiepileptic drug in NEET-PG due to its unique **non-linear (zero-order) kinetics** and a narrow therapeutic index (10–20 µg/mL). ### **Explanation of the Correct Answer** **Ataxia** is a **dose-dependent** (concentration-dependent) side effect. As plasma levels rise above the therapeutic range, phenytoin causes cerebellar-vestibular dysfunction. The progression typically follows a predictable pattern: * **>20 µg/mL:** Nystagmus (earliest sign) * **>30 µg/mL:** **Ataxia**, slurred speech, and diplopia * **>40 µg/mL:** Mental confusion, lethargy, and coma ### **Why Other Options are Incorrect** Options B, C, and D are all recognized side effects of phenytoin, but they are **non-dose-dependent** (chronic) side effects. They occur due to long-term use rather than acute toxicity: * **Gum Hypertrophy:** Occurs due to overgrowth of gingival collagen (stimulated by PDGF). * **Osteomalacia:** Phenytoin induces Cytochrome P450 enzymes, increasing the metabolism of Vitamin D, leading to hypocalcemia. * **Hirsutism:** Excessive hair growth is a common cosmetic side effect in chronic users. ### **High-Yield Clinical Pearls for NEET-PG** * **Mnemonic for Phenytoin Side Effects (HOT MALAI):** **H**irsutism, **O**steomalacia, **T**eratogenicity (Fetal Hydantoin Syndrome), **M**egaloblastic anemia (folate deficiency), **A**taxia, **L**ymphadenopathy, **A**rrhythmias (on rapid IV injection), **I**nsulin inhibition (hyperglycemia). * **Fetal Hydantoin Syndrome:** Characterized by cleft lip/palate and digital hypoplasia. * **Zero-order kinetics:** Small dose increases can lead to disproportionately large increases in plasma levels because metabolic enzymes (CYP2C9) become saturated.

Q: Vigabatrine is the drug of choice for which of the following conditions?

Infantile spasms. **Explanation:** **Infantile Spasms (West Syndrome)** is the correct answer. Vigabatrin is considered the drug of choice specifically for infantile spasms associated with **Tuberous Sclerosis**. Its mechanism of action involves the irreversible inhibition of **GABA transaminase**, the enzyme responsible for the degradation of GABA. This leads to increased levels of GABA (the primary inhibitory neurotransmitter) in the synaptic cleft, effectively suppressing the characteristic spasms. **Analysis of Incorrect Options:** * **A. Febrile Seizures:** The management of choice is usually reassurance or rectal diazepam (if prolonged). Long-term prophylaxis is generally avoided, but if necessary, phenobarbital or sodium valproate is used. * **B. Myoclonic Epilepsy:** Sodium Valproate is the drug of choice. Vigabatrin is actually contraindicated here as it can aggravate myoclonic and absence seizures. * **C. Partial Seizures:** While Vigabatrin is effective as an adjunctive therapy for refractory focal (partial) seizures, it is not the "drug of choice" due to its side effect profile. Carbamazepine or Levetiracetam are typically preferred. **High-Yield Clinical Pearls for NEET-PG:** * **Visual Field Defects:** The most significant adverse effect of Vigabatrin is **permanent bilateral concentric visual field constriction** (retinotoxicity), necessitating regular perimetry monitoring. * **West Syndrome Triad:** Infantile spasms, mental retardation, and a characteristic EEG pattern known as **Hypsarrhythmia**. * **Alternative Treatment:** For infantile spasms *not* caused by Tuberous Sclerosis, **ACTH** or oral prednisolone is often the first-line preference.

Q: Which anti-convulsants are frequently used in the management of trigeminal neuralgia?

All of the above. **Explanation:** Trigeminal neuralgia is characterized by sudden, severe, brief, stabbing, and recurrent episodes of pain in the distribution of one or more branches of the fifth cranial nerve. The primary pharmacological goal is to reduce the hyperexcitability of the trigeminal nerve and its nucleus. **Why "All of the Above" is correct:** While **Carbamazepine** remains the first-line drug of choice (DOC) for trigeminal neuralgia, several other agents are frequently used as alternatives or adjuncts: * **Phenytoin (Option A):** It was the first drug used for this condition. It works by blocking voltage-gated sodium channels, thereby stabilizing neuronal membranes and preventing repetitive firing. * **Gabapentin (Option B):** This is a structural analogue of GABA that binds to the $\alpha_2\delta$ subunit of voltage-gated calcium channels. It is highly effective, especially in patients who do not tolerate Carbamazepine or those with Multiple Sclerosis-associated neuralgia. * **Baclofen (Option C):** Although primarily a $GABA_B$ receptor agonist (skeletal muscle relaxant), it is frequently used in trigeminal neuralgia to enhance pre-synaptic inhibition. It is often used in combination with Carbamazepine or Phenytoin for a synergistic effect. **High-Yield Clinical Pearls for NEET-PG:** * **Drug of Choice:** Carbamazepine is the gold standard/first-line treatment. * **Second-line/Adjuncts:** Oxcarbazepine, Baclofen, Lamotrigine, and Gabapentin. * **Surgical Management:** If medical therapy fails, **Microvascular Decompression (Janetta procedure)** is the definitive surgical treatment. * **Mechanism Focus:** Most effective drugs for this condition work by inhibiting sodium channels or enhancing GABAergic inhibition to dampen paroxysmal neuronal discharges.

Question 1

Which of the following is a 5-HT2A antagonist drug?

Accepted Answer

Ketanserin

Answer

Clozapine

Answer

Cisapride

Answer

Sumatriptan

Question 2

Which of the following local anesthetics is suitable for a patient with hypertension and heart disease?

Accepted Answer

Prilocaine and felypressin

Answer

Lignocaine without adrenaline

Answer

Prilocaine

Answer

Lignocaine with adrenaline 1:1000

Question 3

Which drug is used in absence seizures and has a narrow spectrum of antiepileptic activity?

Accepted Answer

Ethosuximide

Answer

Lamotrigine

Answer

Sodium valproate

Answer

Primidone

Question 4

Which of the following agents does not act via GABAA-Cl– channel complex receptors?

Accepted Answer

Promethazine

Answer

Zopiclone

Answer

Benzodiazepines

Answer

Thiopentone

Question 5

What is the drug of choice for status epilepticus?

Accepted Answer

Lorazepam

Answer

Valproate

Answer

Phenytoin

Answer

Carbamazepine

Question 6

Lignocaine can be used in all of the following conditions except?

Accepted Answer

Convulsions

Answer

Ventricular fibrillation

Answer

Spinal anesthesia

Answer

Epidural anesthesia

Question 7

What is the side effect of phenytoin when its plasma concentration is above the therapeutic level?

Accepted Answer

Ataxia

Answer

Gum hypertrophy

Answer

Osteomalacia

Answer

Hirsutism

Question 8

What is the therapeutic indication of Donepezil?

Accepted Answer

Alzheimer's disease

Answer

Parkinsonism

Answer

Multiple sclerosis

Answer

Myasthenia gravis

Question 9

Vigabatrine is the drug of choice for which of the following conditions?

Accepted Answer

Infantile spasms

Answer

Febrile seizures

Answer

Myoclonic epilepsy

Answer

Partial seizures

Question 10

Which anti-convulsants are frequently used in the management of trigeminal neuralgia?

Accepted Answer

All of the above

Answer

Phenytoin

Answer

Gabapentin

Answer

Baclofen

Central Nervous System Pharmacology — MCQs

Central Nervous System Pharmacology — MCQs

On this page

Practice by Chapter

Want unlimited practice?