Central Nervous System Pharmacology Practice Questions

Q: Which of the following is a centrally acting skeletal muscle relaxant?

Carisoprodol. **Explanation:** Skeletal muscle relaxants are broadly classified into two categories: **Peripherally acting** (acting at the neuromuscular junction or on the muscle fiber) and **Centrally acting** (acting on the spinal cord or brainstem). **1. Why Carisoprodol is Correct:** **Carisoprodol** is a centrally acting muscle relaxant. It works primarily by depressing polysynaptic reflexes in the spinal cord and subcortical areas of the brain. It is metabolized into **meprobamate**, which has sedative and anxiolytic properties. It is typically used for the relief of acute, painful musculoskeletal conditions (e.g., muscle spasms). **2. Why the Other Options are Incorrect:** * **Dantrolene:** This is a **directly acting** muscle relaxant. It acts peripherally on the muscle fiber by inhibiting the release of calcium from the sarcoplasmic reticulum (via RyR1 receptors). It is the drug of choice for Malignant Hyperthermia. * **Gallamine:** This is a **peripherally acting**, non-depolarizing (competitive) neuromuscular blocking agent. It acts by blocking nicotinic receptors ($N_m$) at the motor endplate. * **Succinylcholine:** This is a **peripherally acting**, depolarizing neuromuscular blocker. It acts as an agonist at the $N_m$ receptors, causing persistent depolarization. **High-Yield NEET-PG Pearls:** * **Classification of Centrally Acting Relaxants:** * **GABA-B Agonist:** Baclofen (Drug of choice for spasticity). * **$\alpha_2$ Agonist:** Tizanidine. * **Benzodiazepines:** Diazepam (acts via GABA-A). * **Others:** Cyclobenzaprine, Chlorzoxazone, Metaxalone. * **Meprobamate** (the metabolite of Carisoprodol) carries a high risk of abuse and physical dependence; hence, Carisoprodol is a Schedule IV controlled substance in many regions.

Q: Which of the following statements is FALSE about the drug treatment with Memantine?

It is an NMDA receptor agonist. **Explanation:** The correct answer is **D** because Memantine is an **NMDA receptor antagonist**, not an agonist [1], [2]. **1. Why Option D is False (The Mechanism):** Memantine is a low-to-moderate affinity, non-competitive **NMDA (N-methyl-D-aspartate) receptor antagonist** [1]. In Alzheimer’s disease, overstimulation of NMDA receptors by glutamate leads to excessive calcium influx, causing "excitotoxicity" and neuronal death. Memantine binds to these receptors to block this pathological activation, thereby preserving neuronal function [3]. **2. Analysis of Other Options:** * **Option A (Neuroprotective):** By preventing glutamate-induced excitotoxicity and reducing calcium-mediated cell death, Memantine exerts a neuroprotective effect on surviving neurons [3]. * **Option B (Long Half-life):** Memantine has a clinically significant long terminal half-life of approximately **60 to 80 hours**, allowing for once-daily dosing. * **Option C (Moderate Dementia):** Memantine is specifically FDA-approved for the treatment of **moderate-to-severe** Alzheimer’s disease [3]. It is often used as monotherapy or in combination with Donepezil (an acetylcholinesterase inhibitor) [1]. **High-Yield Clinical Pearls for NEET-PG:** * **Indication:** Unlike Donepezil (used for mild-to-severe), Memantine is typically reserved for **moderate-to-severe** cases [3]. * **Side Effects:** Generally well-tolerated; the most common side effects are dizziness, headache, and confusion [3]. * **Combination Therapy:** The combination of Memantine + Donepezil (Namzaric) shows synergistic benefits in advanced dementia [1]. * **Excretion:** It is primarily excreted unchanged by the kidneys; dose adjustment is required in severe renal impairment.

Q: Levosulpiride acts as an antagonist of which central dopamine receptor?

D2. **Explanation:** **Levosulpiride** is the levo-enantiomer of sulpiride, belonging to the **substituted benzamide** class of drugs. Its primary mechanism of action is the selective and potent **antagonism of central and peripheral Dopamine D2 receptors.** 1. **Why D2 is correct:** At low doses, levosulpiride acts as an antagonist at presynaptic D2 receptors (increasing dopamine release), while at higher doses, it blocks postsynaptic D2 receptors. In the CNS, this blockade provides antipsychotic and antidepressant effects. Peripherally, its D2 antagonism in the gastrointestinal tract makes it a potent **prokinetic agent**, used for dyspepsia and GERD. 2. **Why other options are incorrect:** * **D1:** Levosulpiride has negligible affinity for D1 receptors. D1 receptors are primarily involved in the direct pathway of the basal ganglia. * **D3 and D4:** While some atypical antipsychotics (like Clozapine) have high affinity for D4, and others (like Amisulpride) affect D3, Levosulpiride is highly selective for the **D2** subtype. **High-Yield Clinical Pearls for NEET-PG:** * **Dual Action:** It is used both as an **atypical antipsychotic** and a **prokinetic**. * **Adverse Effects:** Due to D2 blockade in the tuberoinfundibular pathway, it can cause **hyperprolactinemia**, leading to galactorrhea, amenorrhea, and gynecomastia. * **Extrapyramidal Symptoms (EPS):** Although it is an "atypical" agent with lower risk, it can still cause Parkinsonian symptoms or tardive dyskinesia at high doses. * **Comparison:** Unlike Metoclopramide, Levosulpiride is more selective and has a better safety profile regarding CNS side effects at prokinetic doses.

Q: Tolerance develops to all of the following actions of opioids except:

Miosis. **Explanation:** Tolerance is a pharmacological phenomenon where a subject’s reaction to a specific drug concentration is progressively reduced, requiring an increase in dosage to achieve the same effect. In the case of opioids, tolerance develops at different rates for different physiological effects. **Why Miosis is the Correct Answer:** Tolerance develops to almost all pharmacological actions of opioids **EXCEPT** for two specific effects: **Miosis** (pinpoint pupils) and **Constipation**. * **Mechanism:** Miosis occurs due to the stimulation of the Edinger-Westphal nucleus of the IIIrd cranial nerve. The lack of tolerance to miosis is clinically significant because it serves as a reliable diagnostic marker for opioid overdose, even in chronic addicts. **Analysis of Incorrect Options:** * **Analgesia (B):** Tolerance develops rapidly to the pain-relieving effects of opioids. This often necessitates dose escalation in chronic pain management or palliative care. * **Euphoria (C):** Tolerance to the "high" or euphoric effect develops very quickly, which is a primary driver for dose escalation in opioid use disorder. * **Nausea and Vomiting (D):** These effects are mediated by the stimulation of the Chemoreceptor Trigger Zone (CTZ). With repeated administration, most patients develop tolerance to these emetic effects. **High-Yield Clinical Pearls for NEET-PG:** * **Mnemonic for No Tolerance:** Remember **"M.C."** (like a Master of Ceremonies) — **M**iosis and **C**onstipation. * **Rate of Tolerance:** High tolerance develops to Analgesia, Euphoria, Respiratory depression, and Sedation. Moderate tolerance develops to Bradycardia. * **Lethality:** Because tolerance to respiratory depression is high but not absolute, an addict who relapses and takes their previous high dose is at extreme risk of fatal respiratory failure. * **Triad of Opioid Poisoning:** Coma, Pinpoint pupil, and Respiratory depression.

Q: Which of the following statements is FALSE about Naltrexone?

Parenterally administered. **Explanation:** **Naltrexone** is a long-acting opioid antagonist primarily used in the management of opioid and alcohol dependence. **1. Why Option A is False (The Correct Answer):** Naltrexone is characterized by **excellent oral bioavailability**, making it the preferred route for long-term maintenance therapy. Unlike Naloxone, which must be given parenterally due to high first-pass metabolism, Naltrexone is administered **orally** (usually 50 mg once daily). While a long-acting injectable (depot) formulation exists (Vivitrol), the statement that it is "parenterally administered" as a defining characteristic is false in the context of its standard pharmacological profile compared to Naloxone. **2. Analysis of Other Options:** * **Option B (Relapse Prevention):** Naltrexone is FDA-approved for alcohol dependence. It works by blocking the $\mu$-opioid receptors, thereby reducing the "reward" or euphoria associated with alcohol consumption and decreasing cravings. * **Option C (Long Acting):** Naltrexone has a long half-life (approx. 4 hours), but its active metabolite, **6-$\beta$-naltrexol**, has a half-life of about 13 hours. This allows for once-daily dosing, unlike Naloxone, which acts for only 30–90 minutes. * **Option D (Hepatotoxicity):** This is a known dose-related adverse effect. Liver function tests (LFTs) should be monitored in patients on long-term Naltrexone therapy. **High-Yield Clinical Pearls for NEET-PG:** * **Naloxone vs. Naltrexone:** Remember **"O"** for **O**ral (Naltrexone) and **"O"** for **O**pioid Overdose (Naloxone - IV). * **Acamprosate:** Another drug for alcohol relapse; unlike Naltrexone, it is safe in patients with liver disease but contraindicated in renal failure. * **Pre-requisite:** Patients must be opioid-free for at least 7–10 days before starting Naltrexone to avoid precipitating acute withdrawal.

Q: What is the specific antagonist for benzodiazepine?

Flumazenil. ### Explanation **Correct Answer: A. Flumazenil** **Mechanism of Action:** Benzodiazepines (BZDs) work by binding to a specific site on the **GABA-A receptor**, increasing the frequency of chloride channel opening, which leads to neuronal hyperpolarization. **Flumazenil** is a competitive antagonist at this specific BZD binding site. It effectively reverses the sedative effects of benzodiazepines but is less predictable in reversing BZD-induced respiratory depression. **Analysis of Incorrect Options:** * **B. Alprazolam:** This is a short-acting benzodiazepine itself, used primarily for anxiety and panic disorders. It would exacerbate, rather than antagonize, BZD toxicity. * **C. Di-isopropyl phenol:** This is the chemical name for **Propofol**, an intravenous anesthetic agent. It acts via the GABA-A receptor but at a different site than benzodiazepines and has no antagonistic properties. * **D. Naltrexone:** This is an **opioid receptor antagonist** used in the management of opioid addiction and alcohol dependence. It has no effect on the GABA-BZD receptor complex. **High-Yield Clinical Pearls for NEET-PG:** * **Half-life:** Flumazenil has a very short half-life (~1 hour). Since most BZDs (like Diazepam) last longer, **re-sedation** can occur, necessitating repeated doses or an infusion. * **Precipitated Seizures:** The most serious side effect of Flumazenil is the induction of seizures, especially in patients with chronic BZD dependence or those who have co-ingested tricyclic antidepressants (TCAs). * **Indications:** It is used for reversing BZD-induced conscious sedation and in the management of BZD overdose.

Q: Which of the following antiepileptic agents acts on the GABAergic system to decrease the uptake of GABA into neurons and glial cells?

Tiagabine. **Explanation:** The correct answer is **Tiagabine**. To understand why, we must look at the specific mechanism of GABA (Gamma-Aminobutyric Acid) modulation in the synaptic cleft. **1. Why Tiagabine is Correct:** Tiagabine is a selective inhibitor of the **GAT-1 (GABA Transporter-1)**. Under normal physiological conditions, GAT-1 is responsible for the reuptake of GABA from the synaptic cleft into neurons and glial cells (astrocytes). By blocking this transporter, Tiagabine increases the concentration and duration of GABA in the extracellular space, thereby enhancing inhibitory neurotransmission. **2. Why the Other Options are Incorrect:** * **Vigabatrin:** It acts by irreversibly inhibiting **GABA-transaminase (GABA-T)**, the enzyme responsible for the degradation of GABA. It increases GABA levels by preventing its breakdown, not by blocking uptake. * **Progabide:** It is a **GABA receptor agonist** (acting on both GABA-A and GABA-B receptors). It mimics GABA rather than affecting its transport. * **Gabapentin:** Despite its name, it does not act directly on GABA receptors or transporters. Its primary mechanism is the inhibition of **voltage-gated calcium channels** (specifically the $\alpha_2\delta$-1 subunit), which reduces the release of excitatory neurotransmitters like glutamate. **3. High-Yield Clinical Pearls for NEET-PG:** * **Tiagabine Side Effect:** It can occasionally induce non-convulsive status epilepticus in patients without epilepsy. * **Vigabatrin Warning:** Associated with **permanent bilateral visual field constriction** (requires regular perimetry). * **GABA-T vs. GAT-1:** Remember **V**igabatrin for **V**anishing (degrading) GABA via GABA-**T**, and **T**iagabine for **T**ransport (GAT-1) inhibition. * **Drug of Choice:** Tiagabine is primarily used as adjunctive therapy for focal (partial) seizures.

Q: Which one of the following drugs is used to treat status epilepticus?

Diazepam. **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 Diazepam is Correct:** Benzodiazepines (BZDs) are the first-line agents for terminating acute seizures due to their rapid onset of action. **Diazepam** (or Lorazepam) works by enhancing GABA-mediated inhibitory neurotransmission through positive allosteric modulation of the $GABA_A$ receptor. This increases the frequency of chloride channel opening, leading to hyperpolarization and immediate suppression of epileptiform activity. **Why Other Options are Incorrect:** * **Primidone:** A barbiturate derivative metabolized to phenobarbital. It is used for generalized tonic-clonic and partial seizures but is not suitable for acute management due to its slow onset. * **Carbamazepine:** Primarily used for focal seizures and trigeminal neuralgia. It can actually **exacerbate** certain types of seizures (like absence or myoclonic) and is not available in an intravenous formulation for emergency use. * **Sodium Valproate:** While it is a broad-spectrum anti-epileptic used in SE as a second-line agent (after BZDs fail), it is not the initial drug of choice for immediate termination of an ongoing seizure. **High-Yield Clinical Pearls for NEET-PG:** * **Drug of Choice (DOC) for SE:** **Lorazepam (IV)** is often preferred over Diazepam because it has a longer duration of action in the brain (less lipid-soluble, stays in the CNS longer). * **Pre-hospital/IM route:** **Midazolam (IM)** is the preferred choice if IV access is not available. * **Sequence of Management:** 1st line: Benzodiazepines $\rightarrow$ 2nd line: Fosphenytoin/Phenytoin, Valproate, or Levetiracetam $\rightarrow$ 3rd line (Refractory): Phenobarbital, Propofol, or Midazolam infusion.

Question 1

Which of the following statements about Phenytoin is true?

Accepted Answer

It follows zero-order kinetics.

Answer

It is not teratogenic.

Answer

It is excreted unchanged in the urine.

Answer

It does not induce microsomal enzymes.

Question 2

Which of the following is a centrally acting skeletal muscle relaxant?

Accepted Answer

Carisoprodol

Answer

Dantrolene

Answer

Gallamine

Answer

Succinylcholine

Question 3

Which of the following statements is FALSE about the drug treatment with Memantine?

Accepted Answer

It is an NMDA receptor agonist

Answer

It is neuroprotective

Answer

It has a long half-life

Answer

It is used in the treatment of moderate dementia

Question 4

Levosulpiride acts as an antagonist of which central dopamine receptor?

Accepted Answer

D2

Answer

D1

Answer

D3

Answer

D4

Question 5

Tolerance develops to all of the following actions of opioids except:

Accepted Answer

Miosis

Answer

Analgesia

Answer

Euphoria

Answer

Nausea and vomiting

Question 6

Which of the following statements is FALSE about Naltrexone?

Accepted Answer

Parenterally administered

Answer

Used to prevent relapse of heavy drinking

Answer

Long acting

Answer

Can cause hepatotoxicity

Question 7

What is the specific antagonist for benzodiazepine?

Accepted Answer

Flumazenil

Answer

Alprazolam

Answer

Di-isopropyl phenol

Answer

Naltrexone

Question 8

Which of the following antiepileptic agents acts on the GABAergic system to decrease the uptake of GABA into neurons and glial cells?

Accepted Answer

Tiagabine

Answer

Vigabatrin

Answer

Progabide

Answer

Gabapentin

Question 9

Which one of the following drugs is used to treat status epilepticus?

Accepted Answer

Diazepam

Answer

Primidone

Answer

Carbamazepine

Answer

Sodium valporate

Question 10

An antiepileptic drug was found successful for treatment of tonic hind limb extension (THLE). In which type of seizure can this drug be used?

Accepted Answer

General tonic clonic seizures

Answer

Absent seizures

Answer

Myoclonic seizures

Answer

Status epilepticus

Central Nervous System Pharmacology — MCQs

Central Nervous System Pharmacology — MCQs

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