Central Nervous System Pharmacology Practice Questions

Q: Which of the following is a symptom of opiate withdrawal?

Mydriasis. **Explanation:** The correct answer is **A. Mydriasis.** Opioid withdrawal is characterized by a "rebound" hyperactivity of the sympathetic nervous system. While acute opioid toxicity causes **miosis** (pinpoint pupils) due to stimulation of the Edinger-Westphal nucleus, withdrawal leads to the opposite effect: **mydriasis** (pupillary dilation). This occurs because the body, previously suppressed by the depressant effects of opioids, overcompensates when the drug is removed. **Analysis of Options:** * **B. Dry skin and mouth:** Incorrect. Opioid withdrawal is associated with excessive secretions. Patients typically present with **diaphoresis** (sweating), **rhinorrhea** (runny nose), and **lacrimation** (tearing). * **C. Tremors:** While restlessness and anxiety are common, tremors are more characteristic of **Alcohol or Benzodiazepine withdrawal**. Opioid withdrawal is better known for muscle aches, cramps, and "gooseflesh" (piloerection). * **D. Constipation:** Incorrect. Constipation is a classic side effect of opioid *use*. During withdrawal, the GI tract becomes hyperactive, leading to **diarrhea** and abdominal cramping. **NEET-PG High-Yield Pearls:** 1. **Piloerection:** The appearance of "goosebumps" (Cold Turkey) is a highly specific sign of opioid withdrawal. 2. **Yawning:** Frequent yawning is a classic, early clinical sign of the withdrawal syndrome. 3. **Management:** * **Clonidine:** An $\alpha_2$ agonist used to treat autonomic hyperactivity (tachycardia, hypertension) during withdrawal. * **Methadone/Buprenorphine:** Used for long-term substitution therapy. * **Naloxone:** Used for acute toxicity, but can *precipitate* immediate withdrawal in dependent patients.

Q: Which of the following dopamine agonists used in the treatment of Parkinsonism is available as a transdermal patch but not an oral formulation?

Rotigotine. **Explanation:** **Rotigotine** is a non-ergoline dopamine agonist that is uniquely formulated as a **transdermal patch** for the treatment of Parkinson’s disease and Restless Legs Syndrome. It is not available in an oral formulation because it undergoes extensive first-pass metabolism in the liver, leading to poor oral bioavailability. The transdermal delivery system provides continuous drug delivery over 24 hours, ensuring stable plasma levels and reducing "off" periods. **Analysis of Incorrect Options:** * **Apomorphine (Option A):** This is a potent dopamine agonist used for "rescue" therapy during severe "off" episodes. It is administered via **subcutaneous injection** or continuous infusion, not as a patch. It also has poor oral bioavailability. * **Ropinirole (Option B) & Pramipexole (Option D):** These are non-ergoline dopamine agonists commonly used as first-line agents. Both are primarily administered as **oral formulations** (available in immediate and extended-release tablets). **High-Yield NEET-PG Pearls:** * **Rotigotine:** Think "Rotigotine = Rotates on the skin" (Patch). It acts on D1, D2, and D3 receptors. * **Pramipexole:** Has antioxidant properties and is excreted unchanged in the urine (requires dose adjustment in renal failure). * **Ropinirole:** Metabolized by CYP1A2; smoking can induce this enzyme and decrease drug levels. * **Ergot vs. Non-Ergot:** Rotigotine, Ropinirole, and Pramipexole are non-ergot derivatives, meaning they do not carry the risk of cardiac valvular fibrosis associated with older drugs like Bromocriptine or Pergolide.

Q: What is the mechanism of action of Memantine?

Glutaminergic action. **Explanation:** **1. Why Option B is Correct:** Memantine is a drug primarily used in the management of moderate-to-severe Alzheimer’s disease. Its mechanism of action is as a **low-affinity, non-competitive NMDA (N-methyl-D-aspartate) receptor antagonist**. NMDA receptors are a subtype of **glutamate** receptors. In Alzheimer’s, overstimulation of these receptors by glutamate leads to excessive calcium influx, causing "excitotoxicity" and neuronal death. Memantine blocks these receptors under conditions of excessive stimulation, thereby preventing neurodegeneration while allowing normal physiological signaling to occur. **2. Why Other Options are Incorrect:** * **Option A (GABAergic):** GABA is the primary inhibitory neurotransmitter. Drugs like benzodiazepines or barbiturates act here, but they are not used to treat the cognitive decline in Alzheimer's. * **Option C (Adrenergic):** Adrenergic drugs affect the sympathetic nervous system (alpha/beta receptors). They have no direct role in the primary pathology of Alzheimer’s dementia. * **Option D (Dopaminergic):** Dopaminergic agents (like Levodopa) are used in Parkinson’s disease. While some dementia patients have motor symptoms, Memantine does not act on dopamine receptors. **3. High-Yield Clinical Pearls for NEET-PG:** * **Indication:** Specifically approved for **moderate-to-severe** Alzheimer’s (unlike Donepezil, which is used for all stages). * **Combination Therapy:** Often used in combination with Cholinesterase inhibitors (e.g., Donepezil) for synergistic effects. * **Side Effects:** Generally well-tolerated; the most common side effects are dizziness, headache, and confusion. * **Neuroprotection:** It is considered neuroprotective because it prevents glutamate-induced excitotoxicity.

Q: Which of the following is a benzodiazepine receptor antagonist?

Flumazenil. ### Explanation **Correct Option: D. Flumazenil** Flumazenil is a specific **competitive antagonist** at the benzodiazepine (BZD) binding site on the $\text{GABA}_A$ receptor complex. It blocks the effects of benzodiazepines and "Z-drugs" (Zolpidem, Zopiclone) but does not antagonize the effects of barbiturates, ethanol, or general anesthetics, as they bind to different sites on the receptor. **Analysis of Incorrect Options:** * **A. Nalorphine:** A mixed opioid agonist-antagonist. While it can reverse opioid effects, it is rarely used clinically today due to its psychotomimetic side effects. * **B. Carbamazepine:** An anticonvulsant and mood stabilizer that acts primarily by blocking **voltage-gated sodium channels**. It is a first-line treatment for Trigeminal Neuralgia but has no activity at the BZD receptor. * **C. Naloxone:** A competitive **opioid receptor antagonist**. It is the drug of choice for reversing respiratory depression in acute opioid overdose, not BZD overdose. **High-Yield Clinical Pearls for NEET-PG:** * **Indications:** Flumazenil is used for the reversal of BZD-induced conscious sedation and the management of BZD overdose. * **The "Seizure" Risk:** Use flumazenil with extreme caution in patients with long-term BZD dependence or those who have co-ingested TCAs (Tricyclic Antidepressants), as it can precipitate **acute withdrawal seizures**. * **Pharmacokinetics:** It has a very short half-life (~1 hour). Since most benzodiazepines (e.g., Diazepam) last longer, "re-sedation" can occur, requiring repeated doses or an infusion. * **Inverse Agonists:** Remember that **Beta-carbolines** are inverse agonists at the BZD site (causing anxiety/convulsions), and their effects are also blocked by Flumazenil.

Q: What is the mechanism of action of local anesthetics?

Stabilization of the neuronal membrane. ### Explanation **Correct Option: A. Stabilization of the neuronal membrane** Local anesthetics (LAs) act by reversibly binding to the intracellular portion of **voltage-gated sodium channels**. By binding to these channels, they prevent the influx of sodium ions ($Na^+$) into the cell. This prevents the depolarization of the nerve membrane, meaning the threshold potential is never reached and an action potential cannot be generated or conducted. Because the resting membrane potential is maintained and the nerve remains in a non-excitable state, this process is termed **"membrane stabilization."** **Incorrect Options:** * **B & C:** While calcium and magnesium play roles in neurotransmission and membrane excitability, LAs do not primarily target these ions to produce anesthesia. Calcium ions, however, can antagonize the action of LAs (high extracellular $Ca^{2+}$ can decrease LA effectiveness). * **D:** Dopamine release is associated with the central nervous system's reward pathways and motor control; it is not involved in the peripheral block of nerve conduction. **High-Yield NEET-PG Pearls:** * **State-Dependent Block:** LAs have a higher affinity for sodium channels in the **activated (open)** and **inactivated** states rather than the resting state. This is why rapidly firing nerves are blocked faster (use-dependent block). * **Sensitivity:** Small, myelinated fibers (A-delta) and unmyelinated fibers (C-fibers) are generally blocked before large, myelinated fibers. * **Sequence of Blockade:** Autonomic > Sensory (Pain > Temperature > Touch > Proprioception) > Motor. * **Chemistry:** Most LAs are weak bases. In acidic environments (like infected tissue), they become ionized and cannot cross the lipid membrane, leading to reduced efficacy.

Q: Benzodiazepines differ from barbiturates in the following aspects except:

They have a steeper dose-response curve. The core difference between Benzodiazepines (BZDs) and Barbiturates lies in their mechanism of action on the GABA-A receptor and their subsequent safety profiles. **Why Option A is the Correct Answer:** Benzodiazepines actually have a **flatter (shallower) dose-response curve** compared to barbiturates. This is because BZDs are **GABA-facilitatory** (they increase the *frequency* of chloride channel opening) and require endogenous GABA to work. Once GABA receptors are saturated, further increases in BZD dose do not result in further CNS depression. In contrast, Barbiturates have a **steeper dose-response curve** because they are **GABA-mimetic** at high doses (they increase the *duration* of channel opening even in the absence of GABA), leading to progressive CNS depression, coma, and death [1]. **Analysis of Incorrect Options:** * **Option B:** BZDs have a **higher therapeutic index** because of the ceiling effect mentioned above, making them much safer in overdose than barbiturates [2]. * **Option C:** BZDs have **lower abuse liability** and milder withdrawal symptoms compared to the severe physical dependence associated with barbiturates. * **Option D:** BZDs **do not induce** hepatic microsomal enzymes (CYP450), whereas barbiturates are potent enzyme inducers, leading to numerous drug-drug interactions (e.g., with warfarin or oral contraceptives). **High-Yield Clinical Pearls for NEET-PG:** * **Mechanism Mnemonic:** **B**enzodiazepines increase **F**requency (**B-F**); **B**arbiturates increase **D**uration (**B-D**). * **Antidote:** Flumazenil is a specific antagonist for BZD overdose; there is no specific antagonist for barbiturates [1]. * **Contraindication:** Barbiturates are strictly contraindicated in **Acute Intermittent Porphyria** as they induce ALA synthase [1].

Q: Which is the central inhibitor of dopamine metabolism?

Deperenyl. **Explanation:** The correct answer is **Deperenyl** (also known as **Selegiline**). **1. Why Deperenyl is correct:** Dopamine metabolism in the brain occurs primarily via two enzymes: Monoamine Oxidase-B (MAO-B) and Catechol-O-Methyltransferase (COMT). Deperenyl is a selective, irreversible inhibitor of **MAO-B**. By inhibiting this enzyme centrally, it prevents the breakdown of dopamine in the striatum, thereby increasing its bioavailability and prolonging its action. This makes it a key "dopamine sparer" in the management of Parkinson’s disease. **2. Why the other options are incorrect:** * **Carbidopa:** It is a **peripheral** inhibitor of Dopa-decarboxylase. It prevents the conversion of Levodopa to dopamine in the systemic circulation but does not cross the blood-brain barrier (BBB). It does not inhibit dopamine metabolism centrally. * **Orphenadrine:** This is a central **anticholinergic** drug used to manage the cholinergic overactivity (tremors/rigidity) seen in Parkinsonism. It has no direct effect on dopamine metabolism. * **Bromocriptine:** This is a **Dopamine Agonist** (specifically at D2 receptors). It mimics the action of dopamine rather than inhibiting its metabolic breakdown. **3. Clinical Pearls for NEET-PG:** * **MAO Inhibitors:** Selegiline and Rasagiline are selective MAO-B inhibitors. Unlike non-selective MAO inhibitors, they do not typically cause the "Cheese Reaction" (hypertensive crisis) at conventional doses. * **COMT Inhibitors:** **Tolcapone** acts both centrally and peripherally, while **Entacapone** acts only peripherally. * **Metabolic End-product:** The major central metabolite of dopamine is **Homovanillic Acid (HVA)**. * **Drug of Choice:** For drug-induced Parkinsonism, central anticholinergics like **Benztropine** or **Trihexyphenidyl** are preferred over levodopa.

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

Parenterally administered. **Explanation:** **Naltrexone** is a long-acting opioid antagonist used in the management of both Alcohol Use Disorder and Opioid Use Disorder. 1. **Why Option A is FALSE (Correct Answer):** Naltrexone is primarily administered **orally** (50 mg daily). While a long-acting injectable (depot) formulation exists (Vivitrol), the standard pharmacological profile taught for NEET-PG emphasizes its high oral bioavailability and effectiveness via the oral route. In contrast, **Naloxone** (a short-acting antagonist) must be given parenterally because it undergoes extensive first-pass metabolism. Therefore, stating Naltrexone is "parenterally administered" as its defining characteristic is incorrect in this comparative context. 2. **Analysis of Other Options:** * **Option B (Relapse Prevention):** Naltrexone reduces the "high" or craving associated with alcohol by blocking mu-opioid receptors. It is specifically indicated to reduce the frequency of heavy drinking days. * **Option C (Long Acting):** Naltrexone has a significantly longer half-life (approx. 4–13 hours for its active metabolite, 6-beta-naltrexol) compared to Naloxone (approx. 1 hour), making it suitable for maintenance therapy. * **Option D (Hepatotoxicity):** Naltrexone carries a dose-related warning for hepatotoxicity. Liver function tests (LFTs) should be monitored during treatment. **High-Yield Clinical Pearls for NEET-PG:** * **Mechanism:** Competitive antagonist at $\mu$ (mu) receptors. * **Alcoholism:** First-line for reducing cravings (unlike Disulfiram, which is an aversive agent). * **Opioids:** Patients must be opioid-free for **7–10 days** before starting Naltrexone to avoid precipitating acute withdrawal. * **Contraindication:** Acute hepatitis or liver failure.

Q: What is the drug of choice for Restless Legs Syndrome?

Ropinirole. **Explanation:** **Restless Legs Syndrome (RLS)**, also known as Willis-Ekbom Disease, is a neurological sensory-motor disorder characterized by an irresistible urge to move the legs, usually associated with unpleasant sensations that worsen at rest and during the night. **Why Ropinirole is the Correct Answer:** The pathophysiology of RLS is linked to **dopaminergic dysfunction** in the nigrostriatal pathway and iron deficiency in the CNS. Therefore, **Dopamine Agonists** are the first-line treatment (Drug of Choice). **Ropinirole** and **Pramipexole** (non-ergot dopamine agonists) are FDA-approved and preferred because they directly stimulate D2 and D3 receptors, effectively relieving symptoms and improving sleep quality. **Analysis of Incorrect Options:** * **A. Febuxostat:** A xanthine oxidase inhibitor used for the management of chronic hyperuricemia in Gout. It has no role in dopamine modulation. * **B. Diazepam:** A benzodiazepine used for anxiety and muscle spasms. While it may help with sleep onset, it does not treat the underlying sensory-motor urge of RLS and carries a risk of dependence. * **D. Baclofen:** A GABA-B agonist used as a centrally acting muscle relaxant for spasticity (e.g., Multiple Sclerosis). It is not effective for RLS. **High-Yield Clinical Pearls for NEET-PG:** 1. **First-line agents:** Ropinirole, Pramipexole, and Rotigotine (transdermal patch). 2. **Alternative/Second-line:** Gabapentin enacarbil or Pregabalin (preferred if the patient has comorbid neuropathy or insomnia). 3. **Iron Stores:** Always check **Serum Ferritin** levels. Iron supplementation is indicated if ferritin is <75 µg/L, as iron is a cofactor for tyrosine hydroxylase (the rate-limiting enzyme in dopamine synthesis). 4. **Augmentation:** A unique side effect where long-term dopamine agonist use causes symptoms to start earlier in the day or become more severe.

Question 1

Which of the following is a symptom of opiate withdrawal?

Accepted Answer

Mydriasis

Answer

Dry skin and mouth

Answer

Tremors

Answer

Constipation

Question 2

Which of the following dopamine agonists used in the treatment of Parkinsonism is available as a transdermal patch but not an oral formulation?

Accepted Answer

Rotigotine

Answer

Apomorphine

Answer

Ropinirole

Answer

Pramipexole

Question 3

What is the mechanism of action of Memantine?

Accepted Answer

Glutaminergic action

Answer

GABAergic action

Answer

Adrenergic action

Answer

Dopaminergic action

Question 4

Which of the following is a benzodiazepine receptor antagonist?

Accepted Answer

Flumazenil

Answer

Nalorphine

Answer

Carbamazepine

Answer

Naloxone

Question 5

What is the mechanism of action of local anesthetics?

Accepted Answer

Stabilization of the neuronal membrane

Answer

Inhibition of calcium ion influx

Answer

Inhibition of magnesium ion transport

Answer

Increasing dopamine release

Question 6

Benzodiazepines differ from barbiturates in the following aspects except:

Accepted Answer

They have a steeper dose-response curve

Answer

They have a higher therapeutic index

Answer

They have lower abuse liability

Answer

They do not induce microsomal drug-metabolizing enzymes

Question 7

Which is the central inhibitor of dopamine metabolism?

Accepted Answer

Deperenyl

Answer

Carbidopa

Answer

Orphenadrine

Answer

Bromocriptine

Question 8

Allergic reactions in patients who receive amide-type local anesthetics for dental procedures are most likely caused by reaction of what substance?

Accepted Answer

Methylparaben

Answer

Contaminants

Answer

Lignocaine hydrochloride

Answer

Epinephrine

Question 9

Which of the following statements is FALSE regarding Naltrexone?

Accepted Answer

Parenterally administered

Answer

Used to prevent relapse of heavy drinking

Answer

Long acting

Answer

Causes hepatotoxicity

Question 10

What is the drug of choice for Restless Legs Syndrome?

Accepted Answer

Ropinirole

Answer

Febuxostat

Answer

Diazepam

Answer

Baclofen

Central Nervous System Pharmacology — MCQs

Central Nervous System Pharmacology — MCQs

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