Central Nervous System Pharmacology Practice Questions

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.

Q: A patient with Parkinsonism being treated with one of the following drugs developed the skin condition shown in the image. Which drug is most likely responsible for this adverse effect?

Amantadine. ***Amantadine*** - The skin condition shown is **livedo reticularis**, a characteristic adverse effect of amantadine causing a **reticular (net-like) mottling pattern** on the skin. - This occurs due to amantadine's effect on **dopamine and catecholamine-mediated local vasoconstriction**, leading to the distinctive lace-like skin appearance. *Levo-dopa* - Common adverse effects include **dyskinesias**, **nausea**, and **wearing-off phenomena**, but does not cause livedo reticularis. - Skin-related effects are typically **hyperpigmentation** or **melanoma risk**, not the reticular mottling pattern seen here. *Selegiline* - As a **MAO-B inhibitor**, its main adverse effects include **insomnia**, **dizziness**, and potential **hypertensive crisis** with tyramine-rich foods. - Does not cause **livedo reticularis** or any characteristic skin mottling patterns. *Pramipexole* - This **dopamine agonist** commonly causes **impulse control disorders**, **somnolence**, and **peripheral edema**. - Skin manifestations are not typical adverse effects of pramipexole therapy.

Q: What is the drug of choice for tonic-clonic seizures?

Sodium valproate. **Explanation:** **Sodium Valproate** is the drug of choice (DOC) for Generalized Tonic-Clonic Seizures (GTCS) because of its broad-spectrum mechanism of action. It works by increasing GABA levels (inhibitory neurotransmission), blocking voltage-gated sodium channels, and inhibiting T-type calcium channels. This multi-modal action makes it highly effective for generalized epilepsies, especially when the seizure type is not clearly defined or is mixed. **Analysis of Options:** * **Carbamazepine (Option B):** While highly effective for focal (partial) seizures and secondary generalized seizures, it can actually **exacerbate** certain generalized seizures like absence or myoclonic seizures. Therefore, it is not the first-line choice for primary GTCS. * **Phenobarbitone (Option C):** This is a potent anticonvulsant but is no longer the first choice due to its significant side-effect profile, including sedation, cognitive impairment, and behavioral changes in children. It remains a DOC for neonatal seizures in some protocols. * **Felbamate (Option D):** This is a third-line agent reserved for refractory cases (like Lennox-Gastaut syndrome) due to the high risk of life-threatening aplastic anemia and hepatic failure. **High-Yield Clinical Pearls for NEET-PG:** * **Broad Spectrum:** Valproate is the DOC for GTCS, Absence seizures, Myoclonic seizures, and Atonic seizures. * **Teratogenicity:** Valproate is highly teratogenic (causes **Neural Tube Defects**); Levetiracetam or Lamotrigine are preferred in pregnancy. * **Side Effects:** Remember the mnemonic **VALPROATE**: **V**omiting, **A**lopecia, **L**iver toxicity, **P**ancreatitis, **R**etention of weight (obesity), **O**edema, **A**norexia, **T**remors, **E**nzyme inhibitor.

Q: Which of the following agents can be used as a local anesthetic for infiltration if a patient has a documented allergy to both amide and ester anesthetic derivatives?

Diphenhydramine. **Explanation:** **1. Why Diphenhydramine is correct:** In rare cases where a patient is allergic to both **Amides** (e.g., Lidocaine) and **Esters** (e.g., Procaine), **Diphenhydramine**, a first-generation H1-receptor antagonist, serves as an effective alternative for infiltration anesthesia. It possesses significant local anesthetic properties due to its ability to block sodium channels, similar to the mechanism of conventional local anesthetics. While it has a slower onset and shorter duration than lidocaine, it provides sufficient anesthesia for minor procedures (like suturing or biopsies) without cross-reactivity to traditional anesthetic classes. **2. Why other options are incorrect:** * **Nitrous oxide (A):** This is an inhalational anesthetic used for general anesthesia or conscious sedation. It provides systemic analgesia but has no local anesthetic effect when infiltrated into tissues. * **Bupivacaine (B):** This is a potent, long-acting **Amide** local anesthetic. If a patient is allergic to amides, bupivacaine is strictly contraindicated. * **Phenylephrine (C):** This is a selective alpha-1 adrenergic agonist. In local anesthesia, it (or epinephrine) is used as a vasoconstrictor to prolong the duration of action and reduce systemic toxicity, but it does not possess anesthetic properties itself. **3. Clinical Pearls for NEET-PG:** * **Chemical Distinction:** Amides have two "i"s in their name (L**i**doca**i**ne, Bup**i**vaca**i**ne), while Esters have only one (Procaine, Benzocaine). * **Allergy Profile:** True allergies to amides are extremely rare; most reactions are due to the preservative **methylparaben**. Esters are more commonly associated with allergies due to their metabolite, **Para-aminobenzoic acid (PABA)**. * **Concentration:** When using Diphenhydramine for local anesthesia, a **1% concentration** is typically used. Higher concentrations may cause skin necrosis.

Q: Which of the following is NOT an action of opiates in humans?

Mydriasis. The correct answer is **D. Mydriasis**. Opiates (opioid agonists) typically cause **miosis** (pinpoint pupils), not mydriasis [1, 2]. **1. Why Mydriasis is the correct answer (The Exception):** Opioids stimulate the **Edinger-Westphal nucleus** of the oculomotor (III) nerve, leading to parasympathetic overactivity and pupillary constriction (**Miosis**). This is a hallmark sign of opioid overdose. Since the question asks for what is *NOT* an action, Mydriasis (pupillary dilation) is the correct choice. *Note: Pethidine (Meperidine) is a notable exception as it can cause mydriasis due to its atropine-like anticholinergic properties* [3]. **2. Why the other options are incorrect:** * **A. Constipation:** Opioids act on $\mu$-receptors in the myenteric plexus, decreasing intestinal motility and secretions. This is a persistent effect to which tolerance does **not** develop [1, 3]. * **B. Vomiting:** Opioids directly stimulate the **Chemoreceptor Trigger Zone (CTZ)** in the area postrema of the medulla, inducing nausea and vomiting, especially in ambulatory patients [1]. * **C. Analgesia:** This is the primary therapeutic effect. Opioids provide relief by acting on $\mu$-receptors at the supraspinal level and inhibiting pain transmission in the dorsal horn of the spinal cord [1]. **High-Yield Clinical Pearls for NEET-PG:** * **Tolerance:** Tolerance develops to most opioid effects *except* **Miosis** [1, 2] and **Constipation** [1]. * **Triad of Opioid Poisoning:** Coma, Pinpoint pupils, and Respiratory depression. * **Antidote:** **Naloxone** is the drug of choice for acute opioid toxicity. * **Pethidine Exception:** Unlike morphine, Pethidine does not cause miosis (due to anti-muscarinic action) and is preferred in biliary colic as it causes less spasm of the Sphincter of Oddi [3].

Q: All of the following are side effects of Dantrolene therapy except?

Renal dysfunction. **Explanation:** **Dantrolene** is a peripherally acting muscle relaxant that works by binding to the **Ryanodine Receptor (RyR1)** on the sarcoplasmic reticulum. This inhibits the release of calcium into the cytosol, thereby decoupling excitation-contraction coupling in skeletal muscle. **Why Renal Dysfunction is the correct answer:** Dantrolene is primarily metabolized by the liver and excreted in the urine; however, it is **not nephrotoxic**. The most significant organ toxicity associated with chronic Dantrolene use is **Hepatotoxicity** (potentially fatal hepatitis), which requires regular monitoring of Liver Function Tests (LFTs). It does not cause renal dysfunction. **Analysis of Incorrect Options:** * **Muscle Weakness:** This is the most common side effect. Since Dantrolene reduces calcium release in all skeletal muscles (not just the affected ones), generalized weakness and fatigue are expected. * **Phlebitis:** Intravenous Dantrolene is highly alkaline (pH ~9.5) and can be very irritating to peripheral veins, frequently causing injection site reactions and phlebitis. * **Respiratory Insufficiency:** By weakening the diaphragm and intercostal muscles, Dantrolene can decrease vital capacity and cause respiratory embarrassment, especially in patients with pre-existing neuromuscular disease. **High-Yield Clinical Pearls for NEET-PG:** * **Drug of Choice (DOC):** Malignant Hyperthermia (triggered by Halothane/Succinylcholine) and Neuroleptic Malignant Syndrome (NMS). * **Mechanism:** Blocks RyR1 receptors (Calcium channel blocker of the sarcoplasmic reticulum). * **Black Box Warning:** Hepatotoxicity (risk increases if used >60 days or in doses >10 mg/kg/day). * **Contraindication:** It should be avoided in patients with active hepatic disease.

Q: What is the drug of choice for a patient with a combination of primary generalized tonic-clonic seizures and absence seizures?

Valproic acid. **Explanation:** The correct answer is **Valproic acid**. This is based on the clinical principle of managing **mixed seizure disorders** or generalized epilepsy syndromes. **1. Why Valproic Acid is Correct:** Valproic acid is a broad-spectrum antiepileptic drug (AED). Its mechanism of action is multi-modal: it inhibits voltage-gated sodium channels, increases GABA levels (by inhibiting GABA transaminase), and uniquely blocks **T-type Calcium channels** in the thalamus. While Ethosuximide also blocks T-type channels, Valproic acid’s additional mechanisms make it effective against both Absence seizures (thalamic origin) and Generalized Tonic-Clonic Seizures (GTCS). It is the drug of choice for "Idiopathic Generalized Epilepsy" where multiple seizure types coexist. **2. Why Other Options are Incorrect:** * **Ethosuximide:** It is the drug of choice for *isolated* absence seizures. However, it has a narrow spectrum and is **ineffective** against GTCS. * **Carbamazepine & Phenytoin:** These are narrow-spectrum AEDs primarily used for focal seizures and GTCS. Crucially, they can **exacerbate/worsen** absence and myoclonic seizures. **3. NEET-PG High-Yield Pearls:** * **Drug of Choice (DOC) Summary:** * Absence Seizures (Isolated): Ethosuximide. * GTCS, Myoclonic, or Mixed Seizures: Valproic acid. * Trigeminal Neuralgia: Carbamazepine. * Status Epilepticus (Initial): Lorazepam. * **Teratogenicity:** Valproate is highly teratogenic (Neural Tube Defects); **Levetiracetam** or **Lamotrigine** are preferred in pregnancy. * **Side Effects of Valproate:** Hepatotoxicity (monitor LFTs), Pancreatitis, Alopecia, and Weight gain.

Question 1

Which of the following is the least narcotic opioid?

Accepted Answer

Papaverine

Answer

Morphine

Answer

Codeine

Answer

Heroin

Question 2

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

Accepted Answer

Strychnine

Answer

Opium

Answer

Barbiturates

Answer

Gelsemium

Question 3

Which of the following is NOT an ester local anesthetic?

Accepted Answer

Prilocaine

Answer

Cocaine

Answer

Tetracaine

Answer

Chlorprocaine

Question 4

A patient with Parkinsonism being treated with one of the following drugs developed the skin condition shown in the image. Which drug is most likely responsible for this adverse effect?

Accepted Answer

Amantadine

Answer

Levo-dopa

Answer

Selegiline

Answer

Pramipexole

Question 5

What is the drug of choice for tonic-clonic seizures?

Accepted Answer

Sodium valproate

Answer

Carbamazepine

Answer

Phenobarbitone

Answer

Felbamate

Question 6

Which of the following statements regarding barbiturates is accurate?

Accepted Answer

Alkalization of the urine will accelerate the elimination of phenobarbital.

Answer

Benzodiazepines exhibit a steeper dose-response relationship compared to barbiturates.

Answer

Barbiturates may increase the half-lives of drugs metabolized by the liver.

Answer

Respiratory depression caused by barbiturate overdosage can be reversed by flumazenil.

Question 7

Which of the following agents can be used as a local anesthetic for infiltration if a patient has a documented allergy to both amide and ester anesthetic derivatives?

Accepted Answer

Diphenhydramine

Answer

Nitrous oxide

Answer

Bupivacaine

Answer

Phenylephrine

Question 8

Which of the following is NOT an action of opiates in humans?

Accepted Answer

Mydriasis

Answer

Constipation

Answer

Vomiting

Answer

Analgesia

Question 9

All of the following are side effects of Dantrolene therapy except?

Accepted Answer

Renal dysfunction

Answer

Muscle weakness

Answer

Phlebitis

Answer

Respiratory insufficiency

Question 10

What is the drug of choice for a patient with a combination of primary generalized tonic-clonic seizures and absence seizures?

Accepted Answer

Valproic acid

Answer

Ethosuximide

Answer

Carbamazepine

Answer

Phenytoin sodium

Central Nervous System Pharmacology — MCQs

Central Nervous System Pharmacology — MCQs

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