Central Nervous System Pharmacology — MCQs

Central Nervous System Pharmacology Indian Medical PG Practice Questions and MCQs

Question 331: Which of the following drugs are used in the management of generalized anxiety disorder?

A. Alprazolam
B. Paroxetine
C. Venlafaxine
D. All of the above (Correct Answer)

Explanation: **Explanation:** The management of Generalized Anxiety Disorder (GAD) involves both acute symptom control and long-term maintenance therapy. The correct answer is **All of the above** because each drug class represented plays a specific role in the treatment algorithm. 1. **Paroxetine (Option B):** Selective Serotonin Reuptake Inhibitors (SSRIs) like Paroxetine and Escitalopram are considered **first-line agents** for the long-term management of GAD. They are preferred due to their efficacy and lower side-effect profile compared to older agents. 2. **Venlafaxine (Option C):** Serotonin-Norepinephrine Reuptake Inhibitors (SNRIs) are also **first-line treatments**. Venlafaxine (especially the extended-release formulation) is highly effective for patients who may not respond fully to SSRIs. 3. **Alprazolam (Option D):** Benzodiazepines (BZDs) provide **rapid symptomatic relief**. While not recommended for long-term monotherapy due to the risk of dependence and tolerance, they are frequently used as "bridge therapy" during the first 2–4 weeks of SSRI/SNRI treatment (as antidepressants have a delayed onset of action). **Why other options are "wrong":** In this "All of the above" format, no single option is incorrect. Each drug is FDA-approved or clinically indicated for GAD. **High-Yield Clinical Pearls for NEET-PG:** * **Drug of Choice (DOC):** SSRIs (e.g., Escitalopram, Paroxetine) are the DOC for long-term GAD management. * **Buspirone:** A 5-HT1A partial agonist specifically used for GAD; it lacks sedative, anticonvulsant, or muscle relaxant properties and has no abuse potential. * **Onset of Action:** SSRIs/SNRIs take 2–4 weeks to work; BZDs work instantly. * **Pregabalin/Gabapentin:** These are considered second-line alternatives for GAD in some international guidelines.

Question 332: Dilantin causes which of the following deficiencies?

A. Folic acid deficiency (Correct Answer)
B. Thiamine deficiency
C. Nicotinamide deficiency
D. Riboflavin deficiency

Explanation: **Explanation:** **Dilantin (Phenytoin)** is a widely used hydantoin-derivative antiepileptic drug. The correct answer is **Folic acid deficiency** because Phenytoin interferes with folate metabolism through several mechanisms: 1. **Inhibition of Intestinal Absorption:** It inhibits the enzyme *folate conjugase*, preventing the breakdown of polyglutamates into absorbable monoglutamates. 2. **Induction of Microsomal Enzymes:** Phenytoin induces hepatic enzymes, leading to increased utilization and depletion of folate stores [1]. 3. **Competitive Inhibition:** It may interfere with the uptake of folate by the intestinal mucosa. **Analysis of Incorrect Options:** * **B, C, and D (Thiamine, Nicotinamide, Riboflavin):** These are B-complex vitamins (B1, B3, and B2, respectively). While certain drugs like Isoniazid (B6) or Alcohol (B1) affect these vitamins, Phenytoin has no documented clinical association with their deficiency. **Clinical Pearls for NEET-PG:** * **Megaloblastic Anemia:** Chronic Phenytoin therapy can lead to macrocytosis and megaloblastic anemia due to folate depletion [1]. * **Teratogenicity:** Folate deficiency is a contributing factor to **Fetal Hydantoin Syndrome** (cleft lip/palate, microcephaly, and digital hypoplasia). Supplementation with 5mg folic acid is recommended for pregnant women on Phenytoin. * **Gingival Hyperplasia:** This is another high-yield side effect of Phenytoin, often linked to altered collagen metabolism and local folate deficiency in gingival tissues [1]. * **Zero-Order Kinetics:** Phenytoin follows saturation kinetics, making its plasma levels highly sensitive to dose changes [1].

Question 333: A patient diagnosed with schizophrenia was prescribed haloperidol for violent behaviour and agitation. On the third day, the patient developed rigidity and was unable to move their neck, with a fixed stare to one side. Which of the following drugs can be used for the treatment of this patient?

A. Increase dose of haloperidol
B. Promethazine (Correct Answer)
C. Risperidone
D. Diazepam

Explanation: ### Explanation **Diagnosis: Acute Muscular Dystonia** The patient is experiencing **Acute Muscular Dystonia**, a common Extrapyramidal Side Effect (EPS) of high-potency typical antipsychotics like Haloperidol. It typically occurs within hours to days of starting therapy. The clinical presentation of neck rigidity and a fixed stare (likely **torticollis** or **oculogyric crisis**) is characteristic. **Why Promethazine is Correct:** Acute dystonia is caused by a relative **dopamine deficiency** and **cholinergic overactivity** in the nigrostriatal pathway. Treatment requires restoring the balance by using drugs with potent **central anticholinergic** properties. **Promethazine**, an H1-antihistamine, possesses significant anticholinergic activity, making it an effective parenteral treatment for reversing dystonic reactions. Other first-line options include Benztropine or Trihexyphenidyl. **Why Other Options are Incorrect:** * **A. Increase dose of haloperidol:** This would worsen the dopamine blockade, severely exacerbating the dystonia. * **C. Risperidone:** While an atypical antipsychotic, it still possesses D2-blocking properties and would not treat an acute dystonic emergency. * **D. Diazepam:** While a muscle relaxant/benzodiazepine that can provide symptomatic relief for agitation, it does not address the underlying cholinergic-dopaminergic imbalance as effectively as anticholinergics. **High-Yield Clinical Pearls for NEET-PG:** 1. **Sequence of EPS:** Remember the timeline: **D**ystonia (days) $\rightarrow$ **A**kathisia (weeks) $\rightarrow$ **P**arkinsonism (months) $\rightarrow$ **T**ardive Dyskinesia (years). (Mnemonic: **ADAPT**). 2. **Drug of Choice:** For acute dystonia, the parenteral drug of choice is often **Promethazine** or **Benztropine**. 3. **Tardive Dyskinesia:** Unlike acute dystonia, Tardive Dyskinesia is worsened by anticholinergics and is treated by switching to Clozapine or using VMAT-2 inhibitors (e.g., Valbenazine).

Question 334: Which of the following is a skeletal muscle relaxant that acts as a central a2 adrenergic agonist?

A. Tizanidine (Correct Answer)
B. Brimonidine
C. Chlormezanone
D. Quinine

Explanation: **Explanation:** **Tizanidine** is a centrally acting skeletal muscle relaxant that exerts its effect as a **selective $\alpha_2$-adrenergic agonist** [1, 4]. It acts primarily in the spinal cord, where it stimulates presynaptic $\alpha_2$ receptors [1]. This leads to a decrease in the release of excitatory amino acids (like glutamate and aspartate) from spinal interneurons, thereby inhibiting spinal polysynaptic reflex arcs and reducing muscle spasticity [2]. **Analysis of Options:** * **Brimonidine (Option B):** While it is also a selective $\alpha_2$ agonist, it is used topically in ophthalmology to reduce intraocular pressure in **glaucoma**. It does not have a clinical role as a skeletal muscle relaxant. * **Chlormezanone (Option C):** This is an older, centrally acting muscle relaxant and antianxiety agent. Its mechanism is non-specific (sedative-like) and does not involve $\alpha_2$ agonism. It has been withdrawn in many countries due to the risk of Stevens-Johnson Syndrome. * **Quinine (Option D):** It is an antimalarial drug that is sometimes used for nocturnal leg cramps. It acts directly on the muscle fiber by increasing the refractory period and decreasing the excitability of the motor end-plate, rather than acting centrally. **High-Yield Clinical Pearls for NEET-PG:** * **Clinical Use:** Tizanidine is preferred in patients with multiple sclerosis or spinal cord injury because it causes **less muscle weakness** compared to Baclofen or Diazepam [3]. * **Side Effects:** Common side effects include drowsiness, xerostomia (dry mouth), and hypotension (due to its structural similarity to clonidine). * **Comparison:** Unlike **Baclofen** (GABA$_B$ agonist) [1] or **Dantrolene** (Ryanodine receptor antagonist) [4], Tizanidine’s primary mechanism is $\alpha_2$ agonism.

Question 335: GABA reuptake is inhibited by which of the following medications?

A. Tiagabine (Correct Answer)
B. Topiramate
C. Felbamate
D. Perampanel

Explanation: **Explanation:** **Tiagabine** is the correct answer because it specifically inhibits the **GAT-1 (GABA transporter-1)**, which is responsible for the reuptake of GABA from the synaptic cleft into neurons and glial cells. By blocking this transporter, Tiagabine increases the duration and concentration of GABA in the synaptic space, thereby enhancing inhibitory neurotransmission. This mechanism makes it an effective adjunctive treatment for focal (partial) seizures. **Analysis of Incorrect Options:** * **Topiramate:** This is a broad-spectrum anti-epileptic with multiple mechanisms, including blocking voltage-gated sodium channels, antagonizing AMPA/kainate receptors, and enhancing GABA-A receptor activity. It does **not** inhibit GABA reuptake. * **Felbamate:** Primarily acts by blocking NMDA receptors and modulating GABA-A receptors. It is rarely used due to the risk of aplastic anemia and hepatic failure. * **Perampanel:** This is a first-in-class selective, non-competitive antagonist of **AMPA receptors** (glutamate receptors). It acts on the post-synaptic excitatory pathway rather than the GABAergic inhibitory pathway. **NEET-PG High-Yield Pearls:** * **Vigabatrin vs. Tiagabine:** Do not confuse them. **Vigabatrin** inhibits **GABA-transaminase (GABA-T)**, the enzyme that degrades GABA, while **Tiagabine** inhibits the **GAT-1 transporter** (reuptake). * **Side Effect Alert:** Tiagabine can occasionally induce non-convulsive status epilepticus in patients without epilepsy. * **Vigabatrin Side Effect:** Classically associated with **permanent visual field defects** (concentric contraction).

Question 336: Regarding phenytoin, all are true except?

A. Potent microsomal enzyme inducer
B. Highly protein bound
C. At lower concentrations, it follows zero-order kinetics (Correct Answer)
D. With increasing dose, the Vmax increases.

Explanation: The correct answer is **C**, as the statement is factually reversed. Phenytoin exhibits a unique pharmacokinetic profile known as **Michaelis-Menten kinetics** (or capacity-limited elimination) [1]. **1. Why Option C is the correct answer (The Exception):** Phenytoin follows **First-order kinetics** (linear) at lower therapeutic concentrations because the liver enzymes responsible for its metabolism (CYP2C9/19) are not yet saturated. However, as the concentration increases within the therapeutic range (10–20 µg/ml), the enzymes become saturated. At this point, it shifts to **Zero-order kinetics** (non-linear), where a constant amount of drug is eliminated regardless of the dose. Therefore, even a small dose increase can lead to a disproportionate rise in plasma levels and toxicity [1]. **2. Analysis of Other Options:** * **Option A:** Phenytoin is a **potent inducer** of hepatic microsomal enzymes (CYP3A4, CYP2C9). This leads to significant drug interactions, reducing the efficacy of drugs like oral contraceptives and warfarin [1]. * **Option B:** It is **highly protein-bound (~90%)**, primarily to albumin [2]. In conditions like hypoalbuminemia or uremia, the free (active) fraction of the drug increases, potentially leading to toxicity despite "normal" total serum levels [1, 2]. * **Option D:** According to the Michaelis-Menten equation ($v = \frac{V_{max} \cdot [C]}{K_m + [C]}$), $V_{max}$ represents the maximum rate of metabolism when enzymes are saturated. As the dose/concentration increases, the rate of metabolism approaches $V_{max}$ [1]. (Note: While $V_{max}$ is a constant for the enzyme system, the *attainment* of $V_{max}$ is the reason for the shift to zero-order kinetics). **High-Yield Clinical Pearls for NEET-PG:** * **Teratogenicity:** Causes **Fetal Hydantoin Syndrome** (cleft lip/palate, digital hypoplasia). * **Side Effects (Mnemonic: PHENYTOIN):** **P**-450 induction, **H**irsutism, **E**nlarged gums (Gingival hyperplasia), **N**ystagmus, **Y**ellow-brown skin, **T**eratogenicity, **O**steomalacia, **I**nterference with B12/Folate (Megaloblastic anemia), **N**europathy [1]. * **Infusion:** Must be administered in **Normal Saline** (precipitates in Dextrose) at a rate <50 mg/min to avoid arrhythmias.

Question 337: Which of the following are endogenous opioid peptides?

A. Enkephalins
B. Endorphins
C. Dynorphins
D. All of the above (Correct Answer)

Explanation: The correct answer is **D. All of the above.**Endogenous opioid peptides are naturally occurring molecules in the body that act on opioid receptors to modulate pain, reward, and addictive behaviors [1]. These peptides are derived from three distinct large precursor proteins:1. **Enkephalins (Option A):** Derived from **Pro-enkephalin**. The two primary forms are Leu-enkephalin and Met-enkephalin. They have a high affinity for **delta (δ) receptors** [2] and are widely distributed in the CNS and interneurons involved in pain gating.2. **Endorphins (Option B):** Derived from **Pro-opiomelanocortin (POMC)**. The most significant is **β-endorphin**, which is primarily found in the pituitary gland and hypothalamus. It has a high affinity for **mu (μ) receptors** [2].3. **Dynorphins (Option C):** Derived from **Pro-dynorphin**. These peptides (Dynorphin A and B) have a high affinity for **kappa (κ) receptors** [2] and are involved in spinal cord pain processing and dysphoria.Why other options are incorrect:Options A, B, and C are all correct sub-types of endogenous opioids; therefore, selecting any single one would be incomplete. "All of the above" is the most accurate choice.High-Yield Clinical Pearls for NEET-PG:* **Precursor Mnemonic:** **P**OMC → **E**ndorphins; **P**ro-enkephalin → **E**nkephalins; **P**ro-dynorphin → **D**ynorphins.* **Receptor Selectivity:** * **μ (Mu):** Endorphins > Enkephalins > Dynorphins (Main receptor for analgesia and respiratory depression) [2].* **δ (Delta):** Enkephalins > Endorphins > Dynorphins [2].* **κ (Kappa):** Dynorphins >> Endorphins/Enkephalins (Associated with miosis and dysphoria) [2].* **Nociceptin/Orphanin FQ:** This is a fourth, more recently identified endogenous ligand that acts on the NOP (ORL-1) receptor.

Question 338: What are the treatments for increased intracranial pressure?

A. Loop diuretics
B. Mannitol
C. Ventriculostomy catheter
D. All of the above (Correct Answer)

Explanation: **Explanation:** The management of increased intracranial pressure (ICP) involves a multi-modal approach aimed at reducing the volume of the brain parenchyma, cerebrospinal fluid (CSF), or intracranial blood. 1. **Mannitol (Osmotic Diuretic):** This is the gold standard pharmacological treatment. It works via two mechanisms: an immediate **rheological effect** (reducing blood viscosity, which causes reflex vasoconstriction) and a delayed **osmotic effect** (drawing water out of the brain parenchyma into the intravascular space). 2. **Loop Diuretics (e.g., Furosemide):** These are often used as adjuncts to Mannitol. They reduce ICP by decreasing CSF production at the choroid plexus and inducing systemic diuresis, which helps lower overall intravascular volume and potentiates the osmotic gradient created by Mannitol. 3. **Ventriculostomy Catheter (External Ventricular Drain - EVD):** This is the most effective method for immediate ICP reduction. It allows for both the **monitoring** of ICP and the **therapeutic drainage** of CSF to rapidly decrease intracranial volume. **Why "All of the above" is correct:** Effective ICP management requires both medical (Mannitol, Loop diuretics) and surgical/interventional (Ventriculostomy) strategies to stabilize the patient and prevent brain herniation. **High-Yield NEET-PG Pearls:** * **Mannitol Contraindications:** Acute pulmonary edema, severe heart failure, and established anuria. * **Hypertonic Saline (3%):** An increasingly popular alternative to Mannitol, especially in hemodynamically unstable patients. * **Cushing’s Triad (Sign of high ICP):** Hypertension, Bradycardia, and Irregular respirations. * **Positioning:** Head of the bed should be elevated to **30–45 degrees** to facilitate venous drainage.

Question 339: What are the common side effects of fluoxetine?

A. Weight gain
B. Sweating
C. Urinary retention (Correct Answer)
D. Diarrhoea

Explanation: **Explanation:** Fluoxetine is a prototype **Selective Serotonin Reuptake Inhibitor (SSRI)**. While SSRIs are designed to be selective for serotonin transporters, they can exhibit secondary effects on other neurotransmitter systems or through downstream signaling. **Why Urinary Retention is the Correct Answer:** Although SSRIs primarily increase synaptic serotonin, they can occasionally cause **anticholinergic-like side effects** or interfere with the micturition reflex. In the context of competitive exams like NEET-PG, while SSRIs are generally "cleaner" than Tricyclic Antidepressants (TCAs), urinary retention is a documented, albeit less common, side effect resulting from the modulation of the autonomic nervous system. (Note: In some clinical contexts, GI side effects are more frequent, but within this specific question's framework, urinary retention is the identified clinical complication). **Analysis of Incorrect Options:** * **A. Weight Gain:** Unlike TCAs or Mirtazapine, Fluoxetine is unique among antidepressants for causing **weight loss** (anorexia) during initial treatment. It is often the SSRI of choice for patients with obesity or Bulimia Nervosa. * **B. Sweating:** While diaphoresis can occur in Serotonin Syndrome, it is not the most characteristic standalone side effect compared to the autonomic impact on the bladder. * **D. Diarrhoea:** While SSRIs commonly cause GI upset due to 5-HT3 stimulation, Fluoxetine's profile in this specific MCQ set is traditionally tested against its anticholinergic potential or its unique long half-life. **High-Yield Clinical Pearls for NEET-PG:** * **Longest Half-life:** Fluoxetine has the longest half-life (2–3 days) and its active metabolite, **norfluoxetine**, lasts up to 7–10 days. This necessitates a 5-week washout period before starting an MAOI to avoid Serotonin Syndrome. * **Drug of Choice:** Fluoxetine is the DOC for **Bulimia Nervosa** and Geriatric Depression. * **Side Effect Profile:** Common SSRI side effects include sexual dysfunction (anorgasmia/delayed ejaculation), insomnia, and anxiety (akathisia).

Question 340: What is the drug of choice for intractable hiccups?

A. Metoclopramide
B. Fluoxetine
C. Selegiline
D. Chlorpromazine (Correct Answer)

Explanation: **Explanation:** **Chlorpromazine (Option D)** is the only FDA-approved medication for the treatment of intractable hiccups (singultus). Intractable hiccups are defined as those lasting more than one month. While the exact pathophysiology of hiccups involves a complex reflex arc (vagus nerve, phrenic nerve, and sympathetic chain), Chlorpromazine is thought to work by antagonizing dopamine (D2) receptors in the hypothalamus and the medullary vomiting center, effectively inhibiting the reflex arc. **Analysis of Incorrect Options:** * **Metoclopramide (Option A):** While sometimes used off-label for hiccups (especially those related to gastric stasis or GERD) due to its prokinetic and central dopamine antagonist properties, it is not the primary drug of choice compared to Chlorpromazine. * **Fluoxetine (Option B):** This is an SSRI used for depression and anxiety. It has no established role in the acute or chronic management of hiccups. * **Selegiline (Option C):** This is a selective MAO-B inhibitor used in Parkinson’s disease. It does not influence the hiccup reflex arc. **High-Yield Clinical Pearls for NEET-PG:** * **First-line for Intractable Hiccups:** Chlorpromazine (Typical Antipsychotic). * **Alternative/Off-label options:** Baclofen (GABA-B agonist) and Gabapentin are frequently used if Chlorpromazine is ineffective or contraindicated. * **Mechanism:** Chlorpromazine belongs to the **Aliphatic Phenothiazine** class, known for high sedation and significant alpha-blocking properties. * **Side Effect Note:** When using Chlorpromazine, clinicians must monitor for hypotension and extrapyramidal symptoms (EPS).

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