Central Nervous System Pharmacology Practice Questions

Q: A patient with ischemic heart disease is diagnosed with migraine. Which drug is indicated in this case?

Butorphanol. **Explanation:** The management of migraine in patients with **Ischemic Heart Disease (IHD)** requires caution because many standard migraine medications cause systemic vasoconstriction, which can exacerbate myocardial ischemia. **Why Butorphanol is correct:** Butorphanol is a mixed opioid agonist-antagonist (κ-agonist and μ-partial agonist/antagonist). Unlike specific anti-migraine drugs, it does not act on serotonin (5-HT) receptors that cause vasoconstriction. It provides potent analgesia for acute migraine attacks without compromising coronary blood flow, making it a safer alternative for patients with cardiovascular contraindications. **Why the other options are incorrect:** * **Triptans (e.g., Sumatriptan):** These are 5-HT$_{1B/1D}$ agonists. While they effectively constrict cranial vessels, they also cause **coronary vasospasm**. They are strictly contraindicated in patients with IHD, Prinzmetal angina, or uncontrolled hypertension. * **Ergotamines:** These act on 5-HT$_{1}$, 5-HT$_{2}$, and α-adrenergic receptors. They are potent, long-acting vasoconstrictors and are contraindicated in IHD and peripheral vascular disease. * **Propranolol:** While used for migraine **prophylaxis**, it is not indicated for the treatment of an acute attack. Furthermore, in certain cardiac conditions (like vasospastic angina), non-selective beta-blockers can worsen coronary vasoconstriction due to unopposed α-activity. **High-Yield Clinical Pearls for NEET-PG:** * **DOC for Acute Migraine:** Triptans (Sumatriptan). * **DOC for Migraine Prophylaxis:** Propranolol (others include Topiramate, Amitriptyline, and Valproate). * **Newer Drugs (Safe in IHD):** **Lasmiditan** (5-HT$_{1F}$ agonist) and **Gepants** (CGRP antagonists like Rimegepant) are preferred modern alternatives for patients with cardiovascular risks as they do not cause vasoconstriction.

Q: Which drug is primarily used for the treatment of absence seizures?

Lamotrigine. **Explanation:** The drug of choice for **Absence Seizures** (Petit Mal) is traditionally **Ethosuximide** (for pure absence) or **Sodium Valproate** (if associated with tonic-clonic seizures). However, among the given options, **Lamotrigine** is the correct answer as it is a broad-spectrum antiepileptic effective against absence seizures. **1. Why Lamotrigine is Correct:** Lamotrigine acts by blocking voltage-gated sodium channels and inhibiting the release of excitatory neurotransmitters (glutamate and aspartate) [1]. It also has some activity against T-type calcium channels, which are central to the pathophysiology of absence seizures. It is considered a first-line alternative, especially in women of childbearing age, due to its better safety profile compared to Valproate. **2. Why Other Options are Incorrect:** * **Carbamazepine & Phenytoin:** These are narrow-spectrum drugs that block sodium channels. They are strictly **contraindicated** in absence seizures as they can paradoxically worsen the condition or precipitate absence status. * **Vigabatrin:** This drug acts by irreversibly inhibiting GABA transaminase. It is primarily used for Infantile Spasms (West Syndrome) and focal seizures [3]. It is not effective for absence seizures. **Clinical Pearls for NEET-PG:** * **Drug of Choice (DOC):** Ethosuximide (Pure Absence); Valproate (Absence + GTCS). * **Mechanism of Ethosuximide:** Inhibition of **T-type Ca²⁺ channels** in thalamic neurons [2]. * **EEG Finding:** Classic **3 Hz spike-and-wave** discharges. * **Avoid in Absence:** Phenytoin, Carbamazepine, Oxcarbazepine, and Tiagabine (they aggravate the seizure) [2]. * **Lamotrigine Side Effect:** Watch for **Stevens-Johnson Syndrome (SJS)**; the dose must be titrated slowly.

Q: Vigabatrin acts by:

GABA transaminase inhibitor. **Explanation:** **Mechanism of Action (The Correct Answer):** Vigabatrin is an antiepileptic drug that acts as an **irreversible inhibitor of GABA transaminase (GABA-T)**. GABA-T is the enzyme responsible for the metabolic degradation of Gamma-Aminobutyric Acid (GABA), the primary inhibitory neurotransmitter in the brain. By inhibiting this enzyme, Vigabatrin significantly increases the concentration of GABA in the synaptic cleft, leading to enhanced inhibitory neurotransmission and suppression of seizure activity. **Analysis of Incorrect Options:** * **Option A (GABA receptor inhibitor):** This would be pro-convulsant (e.g., Bicuculline). Vigabatrin enhances GABAergic tone rather than inhibiting the receptor. * **Option B (Glutamate receptor inhibitor):** While drugs like Perampanel (AMPA antagonist) or Felbamate (NMDA antagonist) work here, Vigabatrin does not affect glutamate receptors directly. * **Option C (GABA transport inhibitor):** This describes the mechanism of **Tiagabine**, which inhibits the GAT-1 transporter to prevent GABA reuptake. **High-Yield Clinical Pearls for NEET-PG:** * **Drug of Choice (DOC):** Vigabatrin is the first-line treatment for **Infantile Spasms (West Syndrome)** associated with **Tuberous Sclerosis**. * **Adverse Effect:** The most characteristic side effect is **permanent bilateral concentric visual field contraction** (visual field defects), necessitating regular perimetry monitoring. * **Mnemonic:** **Vi**gabatrin **G**ABA **T**ransaminase inhibitor (**Vi-GA-T**). * **Excretion:** It is primarily excreted unchanged by the kidneys; dose adjustment is required in renal impairment.

Q: Morphine can be used in all the following conditions except?

Head injury. **Explanation:** **1. Why Head Injury is the Correct Answer (Contraindication):** Morphine is strictly contraindicated in head injuries due to two primary reasons: * **Respiratory Depression & Increased ICP:** Morphine causes respiratory depression, leading to CO₂ retention (hypercapnia). CO₂ is a potent cerebral vasodilator, which increases cerebral blood flow and further elevates **Intracranial Pressure (ICP)**, potentially causing brain herniation. * **Masking of Clinical Signs:** Morphine causes **miosis** (pinpoint pupils) and sedation. This masks critical neurological signs such as pupillary changes and level of consciousness (GCS score), which are essential for monitoring the progression of a head injury. **2. Analysis of Other Options:** * **Asthma:** While Morphine can cause histamine release and worsen bronchospasm, it is a *relative* contraindication compared to the *absolute* danger in head injuries. * **Hypothyroidism:** Patients with myxedema are highly sensitive to the respiratory depressant effects of opioids due to a low metabolic rate, but it is not the primary contraindication in this specific question context. * **Diabetes:** There is no direct contraindication for using Morphine in diabetic patients, although caution is always advised in chronic metabolic conditions. **3. High-Yield Clinical Pearls for NEET-PG:** * **Drug of Choice (DOC):** Morphine is the DOC for pain in **Myocardial Infarction (MI)** and **Acute Left Ventricular Failure (Cardiac Asthma)** because it reduces preload and anxiety. * **Biliary Colic:** Morphine is generally avoided in biliary colic because it causes constriction of the **Sphincter of Oddi** (Pethidine is preferred). * **Triad of Morphine Poisoning:** Coma, Pinpoint pupil, and Depressed respiration. * **Specific Antidote:** **Naloxone** (pure opioid antagonist) is used for acute toxicity.

Q: Which drug is not currently used in the management of Alzheimer's disease?

Tacrine. ### Explanation **1. Why Tacrine is the Correct Answer:** Tacrine was the first centrally acting acetylcholinesterase (AChE) inhibitor approved for Alzheimer’s disease. However, it is **no longer used** in clinical practice due to its significant **hepatotoxicity** (elevation of serum transaminases) and the requirement for frequent dosing (four times daily). Modern clinical guidelines have replaced it with safer, more potent alternatives with better side-effect profiles. **2. Analysis of Incorrect Options:** * **Donepezil (Option C):** A reversible, non-competitive AChE inhibitor. It is the most commonly used drug for Alzheimer’s because of its long half-life (once-daily dosing) and lack of hepatotoxicity. * **Galantamine (Option B):** A competitive AChE inhibitor that also acts as a **nicotinic receptor modulator**, enhancing the action of acetylcholine. It is used for mild-to-moderate Alzheimer's. * **Rivastigmine (Option D):** A "pseudo-irreversible" inhibitor of both AChE and **butyrylcholinesterase**. It is unique because it is available as a **transdermal patch**, which reduces gastrointestinal side effects. **3. High-Yield Clinical Pearls for NEET-PG:** * **Mechanism of Action:** Alzheimer’s is characterized by a cholinergic deficit. These drugs increase acetylcholine levels in the synaptic cleft. * **Memantine:** A NMDA receptor antagonist used for moderate-to-severe Alzheimer’s; it is often combined with Donepezil. * **Side Effects:** Common side effects of AChE inhibitors include "SLUDGE" symptoms (Salivation, Lacrimation, Urination, Diarrhea, GI distress, Emesis) and bradycardia. * **Newer Monoclonal Antibodies:** Keep an eye on **Aducanumab** and **Lecanemab**, which target amyloid-beta plaques.

Q: Which of the following is the least narcotic opioid?

Papaverine. **Explanation:** The correct answer is **Papaverine**. To understand why, we must look at the chemical composition of Opium, which contains two distinct classes of alkaloids: 1. **Phenanthrene derivatives:** These include Morphine, Codeine, and Thebaine. They act on opioid receptors and possess significant analgesic and narcotic (sleep-inducing/addictive) properties. 2. **Benzylisoquinoline derivatives:** These include **Papaverine** and Noscapine. Unlike the phenanthrene group, these do **not** act on opioid receptors. **Why Papaverine is the correct answer:** Papaverine is a non-narcotic alkaloid. Its primary mechanism of action is the inhibition of phosphodiesterase (PDE), leading to an increase in cAMP and direct relaxation of smooth muscles. It lacks analgesic, euphoric, or addictive properties, making it the "least narcotic" (effectively non-narcotic) among the choices. **Analysis of Incorrect Options:** * **Morphine:** The prototypical opioid agonist. It is a potent narcotic used for severe pain but has high abuse potential. * **Codeine:** A natural phenanthrene alkaloid. While less potent than morphine, it is still a narcotic used as an antitussive and mild analgesic. * **Heroin (Diacetylmorphine):** A semi-synthetic phenanthrene. It is highly lipid-soluble, crosses the blood-brain barrier rapidly, and is more narcotic and addictive than morphine. **NEET-PG High-Yield Pearls:** * **Clinical use of Papaverine:** Historically used for visceral spasms and erectile dysfunction (intracavernosal injection), though largely replaced by PDE-5 inhibitors like Sildenafil. * **Noscapine:** Another benzylisoquinoline (non-narcotic) often used as a non-addictive antitussive; it does not cause constipation or respiratory depression. * **Opium source:** Derived from the air-dried milk (latex) of the unripe seed capsule of *Papaver somniferum*.

Q: Respiratory center depression can be caused by all of the following except?

Strychnine. **Explanation:** The correct answer is **Strychnine**. The respiratory center in the medulla is highly sensitive to drugs that modulate inhibitory neurotransmission or opioid receptors. **1. Why Strychnine is the correct answer:** Strychnine is a potent **CNS stimulant**, not a depressant. It acts as a competitive antagonist at **glycine receptors** (primarily in the spinal cord). By blocking glycine—an inhibitory neurotransmitter—strychnine causes disinhibition, leading to generalized excitatory motor activity and "spinal convulsions." Death occurs due to asphyxia caused by sustained spasms of the diaphragm and thoracic muscles, rather than depression of the respiratory center itself. **2. Why the other options are incorrect:** * **Opium (Morphine):** Opioids are classic respiratory depressants. They act on $\mu$-receptors in the brainstem to decrease the responsiveness of the respiratory center to carbon dioxide ($CO_2$). * **Barbiturates:** These drugs enhance GABAergic transmission. In high doses, they directly depress the medullary respiratory center and the mechanisms responsible for rhythmic breathing. * **Gelsemium:** Derived from the "yellow jasmine," it contains alkaloids (like gelsemine) that act as potent CNS depressants, leading to respiratory failure and paralysis. **Clinical Pearls for NEET-PG:** * **Strychnine Poisoning:** Characterized by *Risus sardonicus* (facial grimace) and *Opisthotonus* (archback), mimicking Tetanus. However, unlike Tetanus, muscles relax between convulsions in Strychnine poisoning. * **Antidote for Opioids:** Naloxone (Competitive antagonist). * **Management of Strychnine:** Diazepam (to control convulsions) and avoiding external stimuli.

Q: Which of the following is NOT an ester local anesthetic?

Prilocaine. Local anesthetics (LAs) are chemically classified into two main groups based on the linkage between their aromatic ring and hydrocarbon chain: **Esters** and **Amides**. ### 1. Why Prilocaine is the Correct Answer **Prilocaine** is an **Amide** local anesthetic. The fundamental rule for NEET-PG aspirants to distinguish between the two groups is the **"i" rule**: * **Amides** have two "i"s in their name (e.g., Pr**i**loca**i**ne, L**i**doca**i**ne, Bup**i**vaca**i**ne). * **Esters** have only one "i" in their name (e.g., Coca**i**ne, Proc**i**ne, Benzoca**i**ne). Since Prilocaine contains two "i"s, it belongs to the amide group, making it the correct choice for "NOT an ester." ### 2. Analysis of Incorrect Options * **B. Cocaine:** A naturally occurring ester. It is unique because it is the only LA that causes vasoconstriction by inhibiting norepinephrine reuptake. * **C. Tetracaine:** A long-acting ester used primarily for spinal and topical anesthesia. * **D. Chloroprocaine:** A short-acting ester known for its rapid metabolism by plasma pseudocholinesterase, giving it the lowest potential for systemic toxicity. ### 3. Clinical Pearls for NEET-PG * **Metabolism:** Esters are metabolized by **plasma pseudocholinesterase** (deficiency leads to prolonged action). Amides are metabolized by **liver microsomal enzymes** (CYP450). * **Allergy:** Allergic reactions are more common with **Esters** due to the metabolite **Para-aminobenzoic acid (PABA)**. Amides rarely cause true allergies. * **Prilocaine Specifics:** It is metabolized to *o-toluidine*, which can cause **methemoglobinemia**. The treatment of choice is Methylene Blue. * **Potency/Duration:** Determined by lipid solubility and protein binding, respectively.

Question 1

A patient with ischemic heart disease is diagnosed with migraine. Which drug is indicated in this case?

Accepted Answer

Butorphanol

Answer

Propranolol

Answer

Triptans

Answer

Ergotamines

Question 2

Which drug is primarily used for the treatment of absence seizures?

Accepted Answer

Lamotrigine

Answer

Carbamazepine

Answer

Phenytoin

Answer

Vigabatrine

Question 3

What is the primary therapeutic strategy for dopamine deficiency in the substantia nigra in Parkinson's disease?

Accepted Answer

Provision of metabolites in the tyrosine pathway

Answer

Feedback inhibition of dopamine oxidation

Answer

Competitive inhibition of dopamine biosynthesis from histidine

Answer

Stimulation of monoamine oxidase

Question 4

Vigabatrin acts by:

Accepted Answer

GABA transaminase inhibitor

Answer

GABA receptor inhibitor

Answer

Glutamate receptor inhibitor

Answer

GABA transport inhibitor

Question 5

Which of the following statements regarding the action of local anesthetics is true?

Accepted Answer

In areas with lower pH, the effectiveness of anesthetic agents is reduced.

Answer

There is little relation between H ion concentration and anesthetic activity.

Answer

There is no correlation between H ion concentration and anesthetic activity.

Question 6

Morphine can be used in all the following conditions except?

Accepted Answer

Head injury

Answer

Asthma

Answer

Hypothyroidism

Answer

Diabetes

Question 7

Which drug is not currently used in the management of Alzheimer's disease?

Accepted Answer

Tacrine

Answer

Galantamine

Answer

Donepezil

Answer

Rivastigmine

Question 8

Which of the following is the least narcotic opioid?

Accepted Answer

Papaverine

Answer

Morphine

Answer

Codeine

Answer

Heroin

Question 9

Respiratory center depression can be caused by all of the following except?

Accepted Answer

Strychnine

Answer

Opium

Answer

Barbiturates

Answer

Gelsemium

Question 10

Which of the following is NOT an ester local anesthetic?

Accepted Answer

Prilocaine

Answer

Cocaine

Answer

Tetracaine

Answer

Chlorprocaine

Central Nervous System Pharmacology — MCQs

Central Nervous System Pharmacology — MCQs

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