Central Nervous System Pharmacology Practice Questions

Q: Lamotrigine is known to cause which of the following common side effects?

Rash. **Explanation:** **Lamotrigine** is a broad-spectrum antiepileptic drug (AED) that acts primarily by blocking voltage-gated sodium channels [1], [2] and inhibiting the release of excitatory neurotransmitters like glutamate [1]. **Why "Rash" is correct:** The most significant and characteristic side effect of Lamotrigine is a **maculopapular skin rash**, occurring in approximately 5-10% of patients. While often mild, it can progress to life-threatening hypersensitivity reactions such as **Stevens-Johnson Syndrome (SJS)** or **Toxic Epidermal Necrolysis (TEN)**. The risk is significantly higher if the drug is started at a high dose or escalated too rapidly, which is why a "start low, go slow" titration schedule is mandatory in clinical practice. **Analysis of Incorrect Options:** * **Irritability & Behavioral disturbances:** These are more commonly associated with **Levetiracetam**. While Lamotrigine is generally well-tolerated and even has mood-stabilizing properties (used in Bipolar Disorder), Levetiracetam is notorious for causing "Levy-rage" or behavioral agitation. * **Nephrotoxicity:** Lamotrigine is primarily metabolized by the liver (glucuronidation). It is not typically nephrotoxic. Drugs like Lithium or certain NSAIDs are more frequently associated with renal side effects in a CNS context. **High-Yield Clinical Pearls for NEET-PG:** * **Drug Interaction:** **Valproate** inhibits the metabolism of Lamotrigine, doubling its half-life and significantly increasing the risk of SJS. Conversely, Carbamazepine and Phenytoin decrease Lamotrigine levels. * **Clinical Use:** It is the preferred AED for **pregnancy** (low teratogenic risk) and is highly effective for **Lennox-Gastaut Syndrome** and **Bipolar Depression**. * **Mechanism:** Sodium channel blockade + Inhibition of Glutamate release [1].

Q: All are true about bupivacaine EXCEPT?

Less cardiotoxic than lignocaine. The correct answer is **A. Less cardiotoxic than lignocaine**. This statement is false because Bupivacaine is significantly **more cardiotoxic** than Lignocaine. ### Explanation of Options: * **Option A (Correct):** Bupivacaine has a high affinity for voltage-gated sodium channels in the myocardium. It dissociates very slowly during diastole ("slow-in, slow-out" kinetics), leading to cumulative block, ventricular arrhythmias, and refractory cardiac arrest. In contrast, Lignocaine dissociates rapidly ("fast-in, fast-out"), making it safer and even useful as an anti-arrhythmic. * **Option B:** Adding adrenaline (epinephrine) causes vasoconstriction, which slows systemic absorption. This allows for a higher total dose to be administered safely (Max dose: 2 mg/kg without adrenaline; 2.5–3 mg/kg with adrenaline). * **Option C:** Bupivacaine is highly protein-bound (approx. 95%), which gives it a long duration of action (3–6 hours), making it ideal for postoperative analgesia and labor epidurals. * **Option D:** Bupivacaine is strictly contraindicated for intravenous use (e.g., IVRA/Bier’s block) due to the extreme risk of systemic toxicity (LAST) and cardiac arrest. ### High-Yield NEET-PG Pearls: 1. **Levobupivacaine & Ropivacaine:** These are the S-enantiomers developed specifically to provide similar anesthesia with **reduced cardiotoxicity** compared to racemic Bupivacaine. 2. **Lipid Rescue:** Intravenous **Lipid Emulsion (20% Intralipid)** is the specific antidote for Bupivacaine-induced systemic toxicity. 3. **Potency:** Bupivacaine is 4 times more potent than Lignocaine. 4. **Bier’s Block:** Lignocaine (0.5%) is the drug of choice; Bupivacaine is absolutely contraindicated.

Q: Which of the following is safest to be used in asthmatic patients?

Nitrazepam. **Explanation:** The primary concern when prescribing hypnotics to patients with respiratory compromise, such as asthma or COPD, is **respiratory depression**. **1. Why Nitrazepam is the Correct Answer:** Nitrazepam is a **Benzodiazepine (BZD)**. Benzodiazepines are generally preferred in asthmatic patients because they have a high therapeutic index and cause **minimal respiratory depression** at hypnotic doses. They do not significantly affect the hypoxic drive or carbon dioxide response in healthy individuals or those with mild-to-moderate respiratory disease. **2. Why the Other Options are Incorrect:** * **Phenobarbitone:** As a **Barbiturate**, it is a potent respiratory depressant. Barbiturates decrease the sensitivity of the medullary respiratory center to CO2 and can induce laryngospasm. They are strictly avoided in patients with compromised respiratory function. * **Chloral Hydrate:** This is an older non-benzodiazepine sedative. While less potent than barbiturates, it can still cause respiratory depression and is irritating to the gastric mucosa. It is rarely used in modern practice due to its narrow safety margin compared to BZDs. * **All hypnotics are safe:** This is incorrect because the degree of respiratory depression varies significantly across drug classes (BZDs vs. Barbiturates vs. General Anesthetics). **Clinical Pearls for NEET-PG:** * **Drug of Choice for Insomnia:** Z-drugs (Zolpidem, Zopiclone) are currently preferred over BZDs as they have even less effect on sleep architecture and respiratory drive. * **Specific Contraindication:** Avoid Barbiturates in **Porphyria** (due to enzyme induction) and severe **Asthma/COPD**. * **Antidote:** If BZDs cause respiratory depression (usually in overdose or when combined with alcohol), the specific antagonist is **Flumazenil**.

Q: Which drug does not cause dependence?

LSD. ### Explanation The core concept behind drug dependence is the activation of the **mesolimbic dopaminergic pathway** (the "reward circuit"), which involves dopamine release in the **Nucleus Accumbens** [2]. **1. Why LSD is the correct answer:** LSD (Lysergic acid diethylamide) is a potent hallucinogen that primarily acts as a partial agonist at **5-HT2A receptors** [1], [2]. Unlike opioids or stimulants, hallucinogens do **not** stimulate the mesolimbic dopamine system. Consequently, they do not produce "craving" or compulsive drug-seeking behavior. While users develop rapid **tolerance** (tachyphylaxis), they do not develop physical or psychological dependence or withdrawal symptoms [1]. **2. Why the other options are incorrect:** * **Cannabis:** Acts on **CB1 receptors**, leading to increased dopamine release [4]. Chronic use can lead to "Amotivational Syndrome" and a recognized withdrawal syndrome (irritability, insomnia) [3]. * **Benzodiazepines:** These are positive allosteric modulators of **GABA-A receptors**. Chronic use leads to down-regulation of receptors, resulting in significant physical dependence and potentially life-threatening withdrawal (seizures). * **Opioids:** Act on **$\mu$-opioid receptors**, inhibiting GABAergic interneurons in the VTA, which disinhibits dopamine neurons [2]. They have the highest potential for both physical and psychological dependence. **High-Yield Clinical Pearls for NEET-PG:** * **Drugs with NO dependence:** LSD, Psilocybin, Mescaline (Hallucinogens) [1]. * **Flashbacks (Hallucinogen Persisting Perception Disorder):** A unique long-term side effect of LSD where the user re-experiences the "trip" without taking the drug. * **Tachyphylaxis:** LSD shows rapid tolerance due to 5-HT2A receptor down-regulation [1]. * **Most Addictive Substance:** Nicotine is often cited as having the highest addiction potential, while Opioids have the most severe physical dependence.

Q: Which of the following drugs does NOT have abuse liability?

Fluoxetine. **Explanation:** The correct answer is **Fluoxetine**. Abuse liability refers to a drug's potential to be used in a non-medical way, often due to its ability to produce euphoria, sedation, or a "high." **1. Why Fluoxetine is the correct answer:** Fluoxetine is a **Selective Serotonin Reuptake Inhibitor (SSRI)**. Unlike drugs with abuse potential, SSRIs do not cause immediate euphoria or rapid surges in dopamine within the brain's reward system (nucleus accumbens). Their therapeutic effects take weeks to manifest. While abrupt discontinuation can lead to "discontinuation syndrome," they do not cause craving or drug-seeking behavior. **2. Why the other options are incorrect:** * **Buprenorphine:** A partial opioid agonist used in opioid substitution therapy. While it has a "ceiling effect," it still possesses significant abuse liability, especially among opioid-naive individuals. * **Alprazolam:** A high-potency, short-acting **Benzodiazepine**. It is highly addictive due to its rapid onset of action and GABA-ergic sedative effects. It is one of the most commonly abused prescription drugs. * **Dextropropoxyphene:** An opioid analgesic. It was historically widely abused for its narcotic effects before being banned or restricted in many regions due to its toxicity and potential for dependence. **High-Yield Clinical Pearls for NEET-PG:** * **Antidepressants** (SSRIs, SNRIs, TCAs) generally have **zero abuse liability**. * **Zolpidem/Zopiclone (Z-drugs)**: Though marketed as safer, they *do* have abuse potential. * **Ketamine**: An NMDA antagonist used for treatment-resistant depression, it has **high abuse liability** (dissociative effects). * **Tianeptine**: An atypical antidepressant that acts on mu-opioid receptors; it is a notable exception with known abuse potential.

Q: Which of the following is NOT an indication for the use of anticonvulsants?

Diabetic neuropathy. The question contains a technical error in its premise, as **Diabetic Neuropathy** is a well-established indication for anticonvulsants. However, based on the provided key, here is the educational breakdown: ### **Explanation** Anticonvulsants (Antiepileptic Drugs - AEDs) are increasingly used for non-epileptic conditions due to their ability to stabilize excitable membranes and modulate neurotransmitters like GABA and Glutamate. * **Why Diabetic Neuropathy is the "Correct" Answer (Contextual Analysis):** In standard clinical practice, this is actually a **primary indication**. Drugs like **Pregabalin and Gabapentin** are first-line treatments for diabetic neuropathy. If this appeared in a NEET-PG exam with this key, it would likely be a "controversial" or "recalled" question where the examiner might be looking for a more specific psychiatric vs. neurological distinction, or it may be a distractor. * **Chronic Pain (Option A):** Anticonvulsants are widely used for neuropathic chronic pain. Carbamazepine is the drug of choice for **Trigeminal Neuralgia**. * **Bipolar Disorder (Option B):** Several AEDs act as mood stabilizers. **Valproate** and **Carbamazepine** are used for acute mania, while **Lamotrigine** is used for maintenance to prevent depressive episodes. * **Anxiety Disorder (Option C):** Certain AEDs are indicated here; for example, **Pregabalin** is approved for Generalized Anxiety Disorder (GAD). ### **High-Yield Clinical Pearls for NEET-PG** * **Drug of Choice (DOC) for Trigeminal Neuralgia:** Carbamazepine. * **DOC for Absence Seizures:** Ethosuximide (Valproate if generalized tonic-clonic seizures are also present). * **Teratogenicity:** Valproate is associated with Neural Tube Defects (highest risk among AEDs). * **SJS/TEN Risk:** Lamotrigine and Carbamazepine (especially in patients with HLA-B*1502 allele). * **Weight Gain:** Common with Valproate; **Weight Loss** is common with Topiramate and Zonisamide.

Q: Pseudolymphoma can result from long-term use of which medication?

Phenytoin. **Explanation:** **Phenytoin** is a well-known cause of **Pseudolymphoma** (also known as Phenytoin-induced lymphadenopathy). This is a hypersensitivity reaction characterized by fever, skin rash, and generalized lymphadenopathy that clinically and histologically mimics Hodgkin’s or non-Hodgkin’s lymphoma. The condition is usually benign and reversible upon discontinuation of the drug, though in rare cases, it may progress to true malignant lymphoma. **Analysis of Options:** * **Phenytoin (Correct):** It induces a type IV hypersensitivity reaction. It is also associated with "DRESS syndrome" (Drug Reaction with Eosinophilia and Systemic Symptoms). * **Carbamazepine:** While it can cause skin rashes (Stevens-Johnson Syndrome) and blood dyscrasias (aplastic anemia), it is not classically associated with pseudolymphoma. * **Sodium Valproate:** Common side effects include weight gain, hepatotoxicity, alopecia, and pancreatitis, but not lymphadenopathy. * **Phenobarbital:** Primarily causes sedation, cognitive impairment, and osteomalacia; it does not typically cause pseudolymphoma. **High-Yield Clinical Pearls for NEET-PG:** * **Mnemonic for Phenytoin Side Effects (PH_E_NYTOIN):** **P**-P450 inducer, **H**-Hirsutism, **E**-Enlarged gums (Gingival hyperplasia), **N**-Nystagmus, **Y**-Yellow-brown skin (Pigmentation), **T**-Teratogenicity (Fetal Hydantoin Syndrome), **O**-Osteomalacia, **I**-Interference with B12/Folate (Megaloblastic anemia), **N**-Neuropathy & **N**-Nodes (Pseudolymphoma). * **Gingival Hyperplasia:** Caused by increased expression of Platelet-Derived Growth Factor (PDGF). * **Zero-order Kinetics:** Phenytoin follows saturation kinetics at therapeutic doses.

Question 1

Lamotrigine is known to cause which of the following common side effects?

Accepted Answer

Rash

Answer

Irritability

Answer

Nephrotoxicity

Answer

Behavioral disturbances

Question 2

All are true about bupivacaine EXCEPT?

Accepted Answer

Less cardiotoxic than lignocaine

Answer

Dose increases with adrenaline

Answer

Long acting

Answer

Cannot be given intravenously

Question 3

Which of the following is safest to be used in asthmatic patients?

Accepted Answer

Nitrazepam

Answer

Phenobarbitone

Answer

Chloral hydrate

Answer

All hypnotics are safe

Question 4

Blockade of nerve conduction by a local anesthetic is characterized by which of the following?

Accepted Answer

Need to cross the cell membrane to produce the block

Answer

Greater potential to block a resting nerve as compared to a stimulated nerve

Answer

Large myelinated fibers are blocked before the unmyelinated fibers

Answer

Cause consistent change of resting membrane potential

Question 5

Which drug does not cause dependence?

Accepted Answer

LSD

Answer

Cannabis

Answer

Benzodiazepine

Answer

Opioids

Question 6

Which of the following drugs does NOT have abuse liability?

Accepted Answer

Fluoxetine

Answer

Buprenorphine

Answer

Alprazolam

Answer

Dextropropoxyphene

Question 7

Which of the following is NOT an indication for the use of anticonvulsants?

Accepted Answer

Diabetic neuropathy

Answer

Chronic pain

Answer

Bipolar disorder

Answer

Anxiety disorder

Question 8

Sumatriptan is contraindicated in which of the following conditions?

Accepted Answer

Peripheral vascular disease

Answer

Asthma

Answer

Diabetes Mellitus (DM)

Answer

Sepsis

Question 9

Why is the effect of local anesthesia slow in infected tissues?

Accepted Answer

Low extracellular pH that hinders diffusion of the drug into the cell.

Answer

Less vascularity causing poor diffusion of drug.

Answer

Rich in enzymes that metabolize the drug.

Answer

Rich in K+ that inhibits the binding of the drug to the receptor.

Question 10

Pseudolymphoma can result from long-term use of which medication?

Accepted Answer

Phenytoin

Answer

Carbamazepine

Answer

Sodium valproate

Answer

Phenobarbital

Central Nervous System Pharmacology — MCQs

Central Nervous System Pharmacology — MCQs

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