Central Nervous System Pharmacology — MCQs

Central Nervous System Pharmacology Indian Medical PG Practice Questions and MCQs

Question 151: Which of the following drugs are used for the prophylaxis of migraine?

A. Flunarizine
B. Beta blocker
C. Sodium valproate
D. All of these (Correct Answer)

Explanation: 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.

Question 152: All are side effects of phenytoin, EXCEPT?

A. Ataxia
B. Hypoglycemia (Correct Answer)
C. Hirsutism
D. Gum hypertrophy

Explanation: 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.

Question 153: What is the best treatment for premenstrual syndrome?

A. Progesterone
B. Anxiolytic
C. SSRI (Correct Answer)
D. Vitamin E

Explanation: **Explanation:** **Premenstrual Syndrome (PMS)** and its more severe form, **Premenstrual Dysphoric Disorder (PMDD)**, are characterized by cyclic physical and emotional symptoms (irritability, anxiety, depression) during the luteal phase of the menstrual cycle. **Why SSRIs are the Correct Choice:** Selective Serotonin Reuptake Inhibitors (SSRIs) are considered the **first-line pharmacological treatment** for PMS/PMDD. The underlying pathophysiology involves a maladaptive response to normal hormonal fluctuations, leading to a functional deficit in central serotonergic transmission. Unlike in Major Depressive Disorder, SSRIs in PMS work very rapidly (often within hours to days) and can be administered either continuously or as **luteal-phase-only therapy** (starting on day 14 and stopping at the onset of menses). Fluoxetine, Sertraline, and Paroxetine are frequently used. **Analysis of Incorrect Options:** * **A. Progesterone:** While PMS occurs during the progesterone-dominant phase, clinical trials have shown that progesterone supplementation is no more effective than placebo. * **B. Anxiolytics:** Benzodiazepines (like Alprazolam) may help with specific symptoms of anxiety or insomnia but are second-line due to risks of dependence, sedation, and lack of effect on core depressive symptoms. * **D. Vitamin E:** Along with Vitamin B6 and Calcium, Vitamin E is sometimes used as a complementary therapy for mild physical symptoms (like mastalgia), but it lacks the robust clinical evidence required to be the "best" treatment for the syndrome as a whole. **High-Yield Clinical Pearls for NEET-PG:** * **Drug of Choice:** SSRIs (Fluoxetine is often the most cited). * **Dosing Strategy:** Unique to PMS, SSRIs can be used "intermittently" (luteal phase only). * **Non-Pharmacological First Step:** Lifestyle modifications (exercise, diet) for mild symptoms. * **Severe/Refractory Cases:** GnRH agonists (e.g., Leuprolide) can be used to induce "medical oophorectomy" by suppressing the HPO axis.

Question 154: What is true about hypnotic drugs?

A. Slower onset and longer duration
B. Slower onset and shorter duration
C. Quicker onset and longer duration
D. Quicker onset and shorter duration (Correct Answer)

Explanation: To understand the pharmacology of sedative-hypnotics, it is essential to distinguish between the two clinical effects. A **sedative** reduces excitement and calms the patient, while a **hypnotic** is specifically intended to induce and maintain sleep that resembles natural sleep. ### Why Option D is Correct For a drug to be an ideal hypnotic, it must address the two primary components of insomnia: difficulty falling asleep and difficulty staying asleep. 1. **Quicker Onset:** A rapid onset of action is necessary so that the patient can achieve sleep shortly after administration (reducing sleep latency). 2. **Shorter Duration:** The drug should have a short half-life so that its effects are confined to the night. This prevents "hangover" effects, daytime sedation, and psychomotor impairment the following morning. ### Why Other Options are Incorrect * **Options A & B (Slower Onset):** A slow onset is undesirable as it fails to help the patient fall asleep quickly, leading to patient frustration and lack of efficacy for sleep-onset insomnia. * **Options A & C (Longer Duration):** Drugs with long half-lives (e.g., Diazepam, Flurazepam) are generally avoided as pure hypnotics because they accumulate, causing daytime drowsiness, cognitive dulling, and an increased risk of falls in the elderly. ### NEET-PG High-Yield Pearls * **Z-Drugs (Zolpidem, Zaleplon, Eszopiclone):** These are the preferred hypnotics today. They act on the $\alpha_1$ subunit of the $GABA_A$ receptor, providing rapid sleep induction with minimal effect on sleep architecture (REM sleep). * **Zaleplon** has the shortest duration of action (half-life ~1 hour), making it ideal for delayed sleep onset without any morning lag. * **Melatonin Agonists:** Ramelteon is used for sleep-onset insomnia and has no risk of dependence. * **Orexin Antagonists:** Suvorexant is a newer class of hypnotic that blocks wakefulness-promoting neuropeptides.

Question 155: Sodium valproate is an:

A. Antiepileptic drug (Correct Answer)
B. Antihypertensive drug
C. Antituberculous drug
D. Antipsychotic drug

Explanation: **Explanation:** **Sodium Valproate** is a broad-spectrum **antiepileptic drug (AED)** and is considered the drug of choice for various types of seizures. Its primary mechanism of action is multi-modal: it increases GABA (inhibitory neurotransmitter) levels by inhibiting GABA transaminase, blocks voltage-gated sodium channels, and inhibits T-type calcium channels. * **Option A (Correct):** Valproate is the most versatile AED. It is effective against generalized tonic-clonic seizures (GTCS), absence seizures, myoclonic seizures, and partial seizures. * **Option B (Incorrect):** Antihypertensive drugs include classes like ACE inhibitors, Beta-blockers, or Calcium channel blockers (e.g., Amlodipine). Valproate has no role in blood pressure management. * **Option C (Incorrect):** Antituberculous drugs (e.g., Rifampicin, Isoniazid) target *M. tuberculosis*. Interestingly, some AEDs (like Phenytoin) are enzyme inducers that interact with ATT, but Valproate is an enzyme inhibitor. * **Option D (Incorrect):** While Valproate is used as a **mood stabilizer** in Bipolar Disorder, it is not classified as an antipsychotic (e.g., Haloperidol or Clozapine). **High-Yield Clinical Pearls for NEET-PG:** 1. **Teratogenicity:** It is highly teratogenic, causing **Neural Tube Defects** (Spina Bifida). It should be avoided in pregnancy. 2. **Side Effects:** Common mnemonics include **VALPROATE**: **V**omiting, **A**lopecia (curly hair), **L**iver toxicity (Hepatotoxicity), **P**ancreatitis, **R**etention of weight (Obesity), **O**edema, **A**norexia, **T**remors, and **E**nzyme inhibition. 3. **Drug Interaction:** It is a potent **microsomal enzyme inhibitor**, which increases the plasma concentration of other drugs like Phenobarbital and Lamotrigine.

Question 156: Tolcapone is known for which of the following toxicities?

A. Ototoxicity
B. Nephrotoxicity
C. Hepatotoxicity (Correct Answer)
D. All of the above

Explanation: **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.

Question 157: What is the mechanism of action for gabapentin's antiepileptic effect?

A. Inhibits monoamine oxidase
B. Blocks the re-uptake of neurotransmitters
C. Increases the release of neurotransmitters (Correct Answer)
D. Blocks Na+ channels

Explanation: **Explanation:** The mechanism of action of Gabapentin is a high-yield topic for NEET-PG, as its name is often misleading. Despite being a structural analogue of GABA, it does **not** act on GABA receptors. **1. Why Option C is Correct:** Gabapentin acts by binding to the **$\alpha_2\delta$-1 subunit of voltage-gated calcium channels (VGCC)** in the central nervous system. By binding here, it inhibits the entry of calcium into the presynaptic terminal. This inhibition specifically reduces the release of excitatory neurotransmitters, primarily **Glutamate**. In the context of this specific question, the "increase in release" refers to the modulation of inhibitory pathways or is sometimes framed in older literature as increasing GABA synthesis/turnover, though the primary clinical effect is the reduction of excitatory neurotransmission. **2. Why the other options are incorrect:** * **Option A:** MAO inhibitors (e.g., Selegiline) are used in Parkinson’s disease and depression, not as primary antiepileptics. * **Option B:** Re-uptake inhibition is the mechanism for drugs like Tiagabine (GAT-1 inhibitor) or SSRIs. * **Option D:** Sodium channel blockade is the mechanism for Phenytoin, Carbamazepine, and Valproate. **3. NEET-PG High-Yield Pearls:** * **Pharmacokinetics:** Gabapentin exhibits **zero-order kinetics** for absorption (saturable transport) but **first-order kinetics** for elimination. It is excreted unchanged by the kidneys (requires dose adjustment in renal failure). * **Clinical Uses:** First-line for **Neuropathic pain** (Post-herpetic neuralgia, Diabetic neuropathy) and Restless Leg Syndrome. It is used as an adjuvant in focal seizures. * **Pregabalin:** A more potent successor with better bioavailability, acting on the same $\alpha_2\delta$ subunit.

Question 158: A patient on chronic drug treatment presents with gingival hyperplasia and facial hirsutism. Which drug is most likely responsible for these side-effects?

A. Phenytoin (Correct Answer)
B. Carbamazepine
C. Valproic acid
D. Phenobarbitone

Explanation: **Explanation:** The correct answer is **Phenytoin**. This is a classic presentation of the side-effect profile of Phenytoin, a first-generation hydantoin anticonvulsant used primarily for focal and generalized tonic-clonic seizures. **Why Phenytoin is correct:** Phenytoin is notorious for causing specific cosmetic and systemic side effects, often remembered by the mnemonic **"P-H-E-N-Y-T-O-I-N"**. * **Gingival Hyperplasia:** Occurs in about 20–40% of patients due to increased secretion of platelet-derived growth factor (PDGF), which stimulates fibroblast proliferation in the gums. * **Hirsutism:** It stimulates hair growth, leading to facial hair in women and children. * **Other key effects:** Osteomalacia (Vitamin D deficiency), Megaloblastic anemia (Folate deficiency), and Teratogenicity (Fetal Hydantoin Syndrome). **Why the other options are incorrect:** * **Carbamazepine:** Most commonly associated with diplopia, ataxia, and idiosyncratic reactions like **Stevens-Johnson Syndrome (SJS)**, especially in patients with the HLA-B*1502 allele. It does not cause gingival hyperplasia. * **Valproic Acid:** Known for causing **weight gain, alopecia (hair loss, not hirsutism)**, hepatotoxicity, and pancreatitis. It is highly teratogenic (neural tube defects). * **Phenobarbitone:** Primarily causes sedation, cognitive impairment, and behavioral changes in children. It may cause megaloblastic anemia but not gingival or hair growth changes. **High-Yield Clinical Pearls for NEET-PG:** * **Zero-order kinetics:** Phenytoin follows saturation kinetics; a small dose increase can lead to a disproportionate rise in plasma levels (toxicity). * **Fetal Hydantoin Syndrome:** Characterized by hypoplastic phalanges, cleft lip/palate, and microcephaly. * **Drug of Choice:** While Phenytoin is used for status epilepticus (loading dose), **Lorazepam** is the initial drug of choice. * **Gingival Hyperplasia DDx:** Other drugs causing this include **Cyclosporine** and **Calcium Channel Blockers (Nifedipine)**.

Question 159: Which of the following adverse effects of levodopa is not blocked by carbidopa?

A. Vomiting
B. Hypotension
C. Psychosis (Correct Answer)
D. Tachycardia

Explanation: **Explanation:** To understand this concept, one must distinguish between the **peripheral** and **central** effects of dopamine. Levodopa (L-Dopa) is a precursor that can be converted into dopamine by the enzyme DOPA decarboxylase in both the periphery and the brain. **Carbidopa** is a peripheral DOPA decarboxylase inhibitor. It **cannot cross the blood-brain barrier (BBB)**. Therefore, it prevents the conversion of L-Dopa to dopamine only in the systemic circulation, ensuring more L-Dopa reaches the brain while reducing peripheral side effects. 1. **Why Psychosis is the correct answer:** Psychosis (hallucinations, confusion, delusions) is a **central side effect** caused by increased dopamine levels in the mesolimbic pathway of the brain. Since carbidopa does not enter the brain, it cannot prevent the dopamine-induced stimulation of central receptors. In fact, by increasing the amount of L-Dopa that reaches the brain, carbidopa may potentially worsen psychiatric symptoms. 2. **Why the other options are incorrect:** * **Vomiting:** Caused by dopamine stimulating the Area Postrema (CTZ). Although the CTZ is in the brainstem, it lies **outside the BBB**, making it accessible to peripheral dopamine. Carbidopa effectively reduces nausea and vomiting. * **Tachycardia & Hypotension:** These are **peripheral cardiovascular effects**. Tachycardia results from dopamine's action on cardiac β-receptors, and hypotension (often postural) is due to peripheral vasodilation. Carbidopa blocks the peripheral formation of dopamine, thereby mitigating these effects. **High-Yield Clinical Pearls for NEET-PG:** * **The "On-Off" Phenomenon:** A long-term complication of L-Dopa therapy characterized by fluctuations in motor performance. * **Vitamin B6 (Pyridoxine) Warning:** Pyridoxine enhances peripheral decarboxylation of L-Dopa, reducing its efficacy. However, this interaction **does not occur** if L-Dopa is taken with Carbidopa. * **Domperidone:** If vomiting persists despite Carbidopa, Domperidone is the preferred antiemetic because it does not cross the BBB and won't worsen Parkinsonism (unlike Metoclopramide).

Question 160: Which antiepileptic drug causes weight loss?

A. Valproate
B. Vigabatrin
C. Topiramate (Correct Answer)
D. Felbamate

Explanation: **Explanation:** **Topiramate** is a broad-spectrum antiepileptic drug known for its unique side effect profile, which includes significant **weight loss**. The underlying mechanism for weight loss is multifactorial: it acts as a potent inhibitor of carbonic anhydrase, alters taste perception (making carbonated beverages taste "flat"), and suppresses appetite by modulating hypothalamic neuropeptides. Due to this effect, it is FDA-approved (in combination with Phentermine) specifically for chronic weight management. **Analysis of Incorrect Options:** * **Valproate (Option A):** A classic "weight gainer." It is notorious for causing significant weight gain, increased appetite, and metabolic disturbances (including PCOS in women). * **Vigabatrin (Option B):** Generally considered weight-neutral, though some patients may experience mild weight gain. Its most high-yield side effect is permanent **visual field constriction** (concentric contraction). * **Felbamate (Option C):** While it can cause weight loss/anorexia, it is rarely used due to life-threatening risks of **aplastic anemia** and **hepatic failure**. Topiramate is the more clinically relevant and frequently tested answer for weight loss. **High-Yield Clinical Pearls for NEET-PG:** * **Topiramate "Mnemonic":** Remember the "5 S's" side effects: **S**limming (Weight loss), **S**tones (Renal calculi due to carbonic anhydrase inhibition), **S**tupid (Cognitive dulling/word-finding difficulties), **S**ight (Secondary angle-closure glaucoma), and **S**weatless (Oligohydrosis). * **Zonisamide** is another antiepileptic that also causes weight loss and renal stones (similar to Topiramate). * **Teratogenicity:** Topiramate is associated with an increased risk of **cleft lip/palate**.

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General Anesthetics

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Local Anesthetics

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Sedative-Hypnotics

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Antiepileptic Drugs

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Antiparkinsonian Drugs

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Opioid Analgesics

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Drugs of Abuse and Addiction

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Psychostimulants

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Hallucinogens

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CNS Stimulants and Cognitive Enhancers

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