Central Nervous System Pharmacology Practice Questions

Q: Which of the following is a long-acting full agonist oral opiate used for heroin detoxification or long-term maintenance?

Methadone. **Explanation:** **Methadone** is the gold standard for the pharmacological management of opioid use disorder (heroin detoxification and maintenance). Its efficacy lies in its unique pharmacokinetic profile: it is a **synthetic full μ-opioid receptor agonist** with high oral bioavailability and an exceptionally **long half-life (24–52 hours)**. In detoxification, methadone prevents withdrawal symptoms by maintaining stable plasma levels, avoiding the "highs and lows" associated with shorter-acting opioids. In long-term maintenance, it induces cross-tolerance, which "blocks" the euphoric effects of illicit heroin if the patient relapses. **Analysis of Incorrect Options:** * **Morphine:** While a full agonist, it has a relatively short half-life (2–4 hours) and significant first-pass metabolism, making it unsuitable for stable long-term maintenance or preventing withdrawal over a 24-hour period. * **Fentanyl:** It is a highly potent, short-acting synthetic opioid. Due to its rapid onset and short duration of action, it is used for anesthesia and acute pain management, but it would worsen addiction cycles if used for detoxification. **High-Yield NEET-PG Pearls:** * **Mechanism:** Apart from being a μ-agonist, Methadone also acts as an **NMDA receptor antagonist**, which may help in reducing opioid tolerance and managing neuropathic pain. * **Side Effects:** A critical ECG finding associated with Methadone is **QTc interval prolongation**, which can lead to Torsades de Pointes. * **Metabolism:** It is primarily metabolized by **CYP3A4**; inhibitors of this enzyme can increase methadone levels, risking respiratory depression. * **Alternative:** **Buprenorphine** (a partial agonist) is also used for maintenance but has a "ceiling effect" on respiratory depression, making it safer in overdose.

Q: What is the mechanism of action of Tolcapone?

COMT inhibitor. **Explanation:** **Mechanism of Action:** Tolcapone is a potent, reversible inhibitor of the enzyme **Catechol-O-methyltransferase (COMT)**. In the management of Parkinson’s disease, when Levodopa is administered, it is peripheralized by COMT into 3-O-methyldopa. Tolcapone inhibits this process, thereby increasing the bioavailability of Levodopa and extending its half-life. Unlike Entacapone (which acts only peripherally), **Tolcapone acts both peripherally and centrally**, crossing the blood-brain barrier to inhibit central COMT. **Analysis of Incorrect Options:** * **Option A (Dopa decarboxylase inhibitor):** This describes **Carbidopa** and **Benserazide**. These drugs prevent the peripheral conversion of Levodopa to Dopamine but do not affect the COMT pathway. * **Option C (MAO-A inhibitor):** These (e.g., **Moclobemide**) are primarily used as antidepressants. Inhibiting MAO-A in the presence of tyramine-rich foods can lead to a "cheese reaction." * **Option D (MAO-B inhibitor):** This describes **Selegiline** and **Rasagiline**. While these are used in Parkinson’s, they work by inhibiting the central breakdown of dopamine rather than the COMT-mediated metabolism of Levodopa. **High-Yield Clinical Pearls for NEET-PG:** * **The "Wearing-Off" Effect:** COMT inhibitors are specifically used to reduce "off" time in patients experiencing fluctuations in Levodopa response. * **Hepatotoxicity:** Tolcapone is associated with a risk of **fulminant hepatic failure**. Therefore, it requires regular liver function test (LFT) monitoring and is generally reserved for patients who do not respond to Entacapone. * **Discoloration:** A common side effect of COMT inhibitors is the harmless **orange discoloration of urine**.

Q: What is the drug of choice for juvenile myoclonic epilepsy?

Valproate. **Explanation:** **Juvenile Myoclonic Epilepsy (JME)**, also known as Janz syndrome, is a common idiopathic generalized epilepsy characterized by myoclonic jerks (typically in the morning), generalized tonic-clonic seizures (GTCS), and occasionally absence seizures. **Why Valproate is the Correct Answer:** Sodium Valproate is the **drug of choice** for JME because it is a broad-spectrum antiepileptic drug (AED) that effectively controls all three seizure types associated with the syndrome. It works by multiple mechanisms: blocking voltage-gated sodium channels, increasing GABA levels, and inhibiting T-type calcium channels. In JME, Valproate provides a high rate of seizure freedom (up to 80-90%), though it is often required lifelong as relapse rates are high upon discontinuation. **Analysis of Incorrect Options:** * **Phenytoin:** This is a narrow-spectrum AED. It is contraindicated in JME because it can **exacerbate** myoclonic jerks and absence seizures. * **Lamotrigine:** While effective for GTCS, Lamotrigine can sometimes worsen myoclonic seizures in JME patients. It is generally considered a second-line agent or an alternative in females of childbearing age. * **Zonisamide:** This is a broad-spectrum agent that may be used as an adjunct, but it is not the first-line gold standard compared to Valproate. **Clinical Pearls for NEET-PG:** * **Teratogenicity:** While Valproate is the most effective, it is highly teratogenic (Neural Tube Defects). In **females of childbearing age**, Levetiracetam or Lamotrigine are preferred alternatives. * **EEG Finding:** JME typically shows characteristic **4-6 Hz polyspike-and-wave** discharges. * **Avoidance:** Drugs that block sodium channels exclusively (Phenytoin, Carbamazepine, Oxcarbazepine) should be avoided in JME as they aggravate myoclonus.

Q: Which of the following drugs are used for the prophylaxis of migraine?

All of these. Migraine management is divided into **Abortive (Acute)** therapy and **Prophylactic (Preventive)** therapy. Prophylaxis is indicated if attacks occur >2–3 times per month, are severe, or if acute treatments are contraindicated. ### Explanation of Options: * **Beta-blockers (e.g., Propranolol):** These are the **first-line** drugs for migraine prophylaxis. They likely work by stabilizing vascular tone and inhibiting cortical spreading depression. Propranolol is the most commonly used agent in this class. * **Flunarizine:** This is a **selective calcium channel blocker** (specifically T-type and L-type). Unlike verapamil, flunarizine is highly effective in reducing the frequency and severity of migraine attacks, though it may cause weight gain and sedation. * **Sodium Valproate:** This **anti-epileptic** drug is an effective prophylactic agent. It works by increasing GABAergic inhibition and modulating excitatory neurotransmitters. Topiramate is another anti-epileptic frequently used for this purpose. Since all three classes—Beta-blockers, Calcium channel blockers, and Anti-epileptics—are established prophylactic agents, **Option D (All of these)** is correct. ### High-Yield Clinical Pearls for NEET-PG: * **DOC for Prophylaxis:** Propranolol (avoid in asthmatics and diabetics). * **DOC for Acute Attack:** Sumatriptan (5-HT$_{1B/1D}$ agonist). * **Tricyclic Antidepressants (TCAs):** Amitriptyline is the preferred prophylactic agent for patients with co-existing tension-type headaches, depression, or insomnia. * **Newer Agents:** **CGRP Antagonists** (e.g., Erenumab) are used for prophylaxis in refractory cases. * **Menstrual Migraine:** Frovatriptan or Naproxen are often used for short-term prophylaxis.

Q: All are side effects of phenytoin, EXCEPT?

Hypoglycemia. Phenytoin is a high-yield topic in NEET-PG due to its narrow therapeutic index and diverse side-effect profile. ### **Explanation of the Correct Answer** **B. Hypoglycemia:** This is the correct answer because Phenytoin actually causes **Hyperglycemia**, not hypoglycemia. Phenytoin inhibits the release of insulin from the pancreas (by stabilizing membranes and reducing calcium influx). This can lead to elevated blood glucose levels and, in some cases, glycosuria. ### **Analysis of Incorrect Options** * **A. Ataxia:** This is a dose-dependent sign of cerebellar toxicity. Along with nystagmus and diplopia, ataxia is one of the earliest signs that phenytoin levels have exceeded the therapeutic range (usually >20 µg/ml). * **C. Hirsutism:** This is a common non-dose-dependent side effect, particularly problematic in young females. It involves the growth of unwanted hair on the face and body. * **D. Gum Hypertrophy:** Also known as gingival hyperplasia, this occurs in about 20% of patients. It is caused by the overgrowth of gingival tissue due to increased fibroblast proliferation and collagen deposition. ### **Clinical Pearls for NEET-PG** To remember the side effects of Phenytoin, use the mnemonic **"HOT MALAI"**: * **H** – Hirsutism, Hypertrophy of gums, Hyperglycemia * **O** – Osteomalacia (due to induced Vitamin D metabolism) * **T** – Teratogenicity (**Fetal Hydantoin Syndrome**: cleft lip/palate, microcephaly) * **M** – Megaloblastic anemia (due to folate interference) * **A** – Ataxia * **L** – Lymphadenopathy (Pseudolymphoma) * **A** – Arrhythmias (when given via rapid IV push) * **I** – Insulin inhibition (leading to Hyperglycemia) **Key Fact:** Phenytoin follows **Zero-order kinetics** (capacity-limited metabolism) at therapeutic or high concentrations, making small dose increases lead to disproportionate rises in plasma levels.

Q: All of the local anesthetics given below are amides, EXCEPT:

Procaine. Local anesthetics (LAs) are chemically classified into two main groups based on the intermediate chain linking the aromatic ring and the amino group: **Amides** and **Esters**. ### 1. Why Procaine is the Correct Answer **Procaine** is an **Ester**-type local anesthetic. Esters are metabolized by plasma pseudocholinesterase and are more likely to cause allergic reactions due to the formation of para-aminobenzoic acid (PABA). **The "i" Rule (Mnemonic):** To differentiate between the two classes for exams: * **Amides** have **two** "i"s in their name (e.g., L**i**doca**i**ne). * **Esters** have only **one** "i" in their name (e.g., Proca**i**ne). ### 2. Analysis of Incorrect Options * **A. Lignocaine (Lidocaine):** An amide. It is the most commonly used LA and serves as the prototype amide. * **C. Prilocaine:** An amide. It is known for causing methemoglobinemia at high doses due to its metabolite, o-toluidine. * **D. Etidocaine:** An amide. It is a long-acting agent characterized by a profound motor block. ### 3. Clinical Pearls for NEET-PG * **Metabolism:** Amides are metabolized in the **liver** (by CYP450 enzymes), while Esters are metabolized in the **plasma** (by pseudocholinesterase). * **Cocaine** is the only naturally occurring ester and the only LA that causes **vasoconstriction** (others are vasodilators). * **Bupivacaine** is the most cardiotoxic LA; **Levobupivacaine** and **Ropivacaine** are safer S-enantiomer alternatives. * **Benzocaine** is an ester used topically; it is also a common cause of methemoglobinemia.

Q: Peripheral vasospasm is an adverse effect of which drug?

Bromocriptine. **Explanation:** The correct answer is **Bromocriptine**. **1. Why Bromocriptine is correct:** Bromocriptine is a first-generation **Ergot-derivative** dopamine agonist. Ergot derivatives are notorious for causing potent vasoconstriction due to their partial agonist activity on alpha-adrenergic receptors and serotonin receptors. This leads to **peripheral vasospasm**, which can manifest clinically as **Raynaud’s phenomenon** or digital ischemia. Long-term use of ergot derivatives is also associated with fibrotic complications (pleuropulmonary, cardiac, and retroperitoneal fibrosis). **2. Why the other options are incorrect:** * **Ropinirole and Pramipexole (Options A & D):** These are **Non-ergot** dopamine agonists. They are highly selective for D2 and D3 receptors and lack the ergot-ring structure. Consequently, they do not cause peripheral vasospasm or systemic fibrosis. Their common side effects include nausea, orthostatic hypotension, and impulse control disorders (e.g., pathological gambling). * **Levodopa (Option B):** As a precursor to dopamine, Levodopa primarily causes peripheral side effects like nausea and cardiac arrhythmias (due to peripheral conversion to catecholamines) or central effects like dyskinesias and hallucinations. It does not cause vasospasm. **3. NEET-PG High-Yield Pearls:** * **Ergot-derivatives:** Bromocriptine, Cabergoline, Pergolide (associated with vasospasm and fibrosis). * **Non-ergot derivatives:** Ropinirole, Pramipexole, Rotigotine, Apomorphine (preferred in younger patients to delay Levodopa use). * **Clinical Sign:** If a patient on Bromocriptine complains of cold, blue fingers in response to cold (Raynaud’s), the drug should be switched to a non-ergot agonist. * **Erythromelalgia:** Paradoxically, Bromocriptine can also cause this condition (red, painful, swollen extremities), though vasospasm is more characteristic of the ergot class.

Q: Tolcapone is known for which of the following toxicities?

Hepatotoxicity. **Explanation:** **Tolcapone** is a COMT (Catechol-O-methyltransferase) inhibitor used as an adjunct to Levodopa/Carbidopa therapy in Parkinson’s disease [1]. Its primary mechanism is to inhibit the peripheral and central breakdown of Levodopa, thereby increasing its bioavailability and duration of action [2]. **Why Hepatotoxicity is the Correct Answer:** The most significant and dose-limiting adverse effect of Tolcapone is **fulminant hepatic failure** [1]. Due to this risk of severe hepatotoxicity, it is generally reserved for patients who do not respond to other treatments. Patients on Tolcapone require mandatory, periodic monitoring of liver function tests (LFTs). This is in contrast to **Entacapone**, another COMT inhibitor, which is not associated with hepatotoxicity and is more commonly used in clinical practice [2]. **Why Other Options are Incorrect:** * **Ototoxicity:** This is typically associated with drugs like Aminoglycosides, Loop diuretics, or Cisplatin. Tolcapone has no known effect on the auditory system. * **Nephrotoxicity:** While many drugs are cleared renally, Tolcapone does not cause direct structural or functional damage to the kidneys. Common nephrotoxic agents include NSAIDs, Amphotericin B, and Contrast media. **High-Yield Clinical Pearls for NEET-PG:** * **Tolcapone vs. Entacapone:** Tolcapone acts both **peripherally and centrally**, whereas Entacapone acts only **peripherally** [1][2]. * **Orange Discoloration:** Both drugs can cause a harmless orange discoloration of urine. * **The "3 Ls" of Tolcapone:** **L**iver toxicity, **L**onger duration of action (compared to Entacapone), and **L**evodopa-sparing effect. * **Monitoring:** If no clinical improvement is seen within 3 weeks, Tolcapone should be discontinued due to the risk-benefit ratio regarding the liver.

Q: What is the most common drug used for prophylaxis of migraine?

Propranolol. **Explanation:** **Propranolol** is considered the **first-line drug of choice** for the continuous prophylaxis of migraine. It is a non-selective beta-blocker that works by stabilizing vascular tone, reducing central catecholaminergic hyperactivity, and inhibiting the cortical spreading depression (CSD) associated with migraine pathophysiology. It is particularly effective in patients with co-existing hypertension or anxiety. **Analysis of Options:** * **A. Sumatriptan:** This is a 5-HT$_{1B/1D}$ receptor agonist used for the **acute treatment** of migraine attacks to abort the headache. It is never used for prophylaxis because frequent use can lead to "medication overuse headache." * **C. Valproate:** While sodium valproate is an effective prophylactic agent (especially for patients with comorbid epilepsy), it is generally considered a second-line option due to its side-effect profile (weight gain, hair loss, and teratogenicity). * **D. Flunarizine:** This is a calcium channel blocker used for prophylaxis, particularly in Europe and India. However, due to its side effects (sedation and weight gain) and slower onset of action, it is usually not the first choice over beta-blockers. **High-Yield Clinical Pearls for NEET-PG:** * **Prophylaxis Criteria:** Indicated if attacks occur $>2-3$ times per month or are severely disabling. * **Contraindications for Propranolol:** Avoid in patients with bronchial asthma, heart block, or peripheral vascular disease (Raynaud’s). * **Other Prophylactic Agents:** Amitriptyline (DOC if comorbid depression/insomnia), Topiramate (DOC if the patient is obese, as it causes weight loss), and CGRP antagonists (e.g., Erenumab) for refractory cases. * **DOC in Pregnancy:** Magnesium or low-dose Propranolol (though lifestyle changes are preferred). Avoid Valproate (Category X for migraine).

Question 1

Which of the following is a long-acting full agonist oral opiate used for heroin detoxification or long-term maintenance?

Accepted Answer

Methadone

Answer

Morphine

Answer

Fentanyl

Answer

None of the above

Question 2

What is the mechanism of action of Tolcapone?

Accepted Answer

COMT inhibitor

Answer

Dopa decarboxylase inhibitor

Answer

MAO - A inhibitor

Answer

MAO - B inhibitor

Question 3

What is the drug of choice for juvenile myoclonic epilepsy?

Accepted Answer

Valproate

Answer

Phenytoin

Answer

Lamotrigine

Answer

Zonisamide

Question 4

Which of the following drugs are used for the prophylaxis of migraine?

Accepted Answer

All of these

Answer

Flunarizine

Answer

Beta blocker

Answer

Sodium valproate

Question 5

All are side effects of phenytoin, EXCEPT?

Accepted Answer

Hypoglycemia

Answer

Ataxia

Answer

Hirsutism

Answer

Gum hypertrophy

Question 6

All of the local anesthetics given below are amides, EXCEPT:

Accepted Answer

Procaine

Answer

Lignocaine

Answer

Prilocaine

Answer

Etidocaine

Question 7

Peripheral vasospasm is an adverse effect of which drug?

Accepted Answer

Bromocriptine

Answer

Ropinirole

Answer

Levodopa

Answer

Pramipexole

Question 8

Tolcapone is known for which of the following toxicities?

Accepted Answer

Hepatotoxicity

Answer

Ototoxicity

Answer

Nephrotoxicity

Answer

All of the above

Question 9

What is the most common drug used for prophylaxis of migraine?

Accepted Answer

Propranolol

Answer

Sumatriptan

Answer

Valproate

Answer

Flunarizine

Question 10

A patient on chronic drug treatment presents with gingival hyperplasia and facial hirsutism. Which drug is most likely responsible for these side-effects?

Accepted Answer

Phenytoin

Answer

Carbamazepine

Answer

Valproic acid

Answer

Phenobarbitone

Central Nervous System Pharmacology — MCQs

Central Nervous System Pharmacology — MCQs

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