Central Nervous System Pharmacology Practice Questions

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.

Q: All of the following are true regarding levodopa except?

Levodopa cannot cross the blood-brain barrier.. **Explanation:** **1. Why Option C is the correct (false) statement:** The fundamental principle of treating Parkinson’s disease with Levodopa is that **Levodopa can cross the blood-brain barrier (BBB)** via the large neutral amino acid transporter (LAT). Once inside the CNS, it is decarboxylated to Dopamine [1]. Dopamine itself cannot cross the BBB; therefore, Levodopa acts as a "prodrug" to replenish central dopamine levels. **2. Analysis of other options:** * **Option A:** Levodopa has a very short plasma half-life of approximately **60 to 90 minutes**, which contributes to the need for frequent dosing and the development of motor fluctuations [1]. * **Option B:** Peripheral conversion of Levodopa to dopamine can cause **orthostatic hypotension** (via action on D1 receptors in the vasculature). **Dyskinesias** (involuntary movements) are a common long-term side effect related to fluctuating drug levels and striatal hypersensitivity [2]. * **Option D:** This describes the **"wearing-off" phenomenon** [1]. Initially, the brain can store dopamine, but as the disease progresses and nigrostriatal neurons are lost, the duration of benefit mirrors the drug's short half-life. **High-Yield Clinical Pearls for NEET-PG:** * **Carbidopa/Benserazide:** These are peripheral dopa-decarboxylase inhibitors. They do **not** cross the BBB. They are co-administered with Levodopa to prevent peripheral conversion, thereby increasing the amount of Levodopa reaching the brain and reducing peripheral side effects like nausea/vomiting [1]. * **Vitamin B6 (Pyridoxine):** It is a cofactor for decarboxylase. High doses of B6 can increase peripheral metabolism of Levodopa, reducing its efficacy (unless a decarboxylase inhibitor is used). * **Contraindication:** Levodopa can activate latent melanoma; hence, it is contraindicated in patients with suspicious undiagnosed skin lesions.

Q: Which of the following drugs is used worldwide for the maintenance therapy of opioid dependence?

Methadone. **Explanation:** The management of opioid dependence involves two phases: detoxification and **maintenance therapy**. **Methadone** is a long-acting synthetic **mu-opioid receptor agonist**. Its efficacy in maintenance therapy stems from its long half-life (24–36 hours), which prevents withdrawal symptoms and provides a "blockade effect" by inducing cross-tolerance; this prevents the euphoria associated with illicit heroin use. Because it is administered orally, it breaks the ritual of intravenous drug use, allowing for social rehabilitation. **Analysis of Options:** * **Naltrexone (Option A):** While used in opioid de-addiction, it is an **opioid antagonist**. It is used to prevent relapse in highly motivated patients who are already detoxified. It is not the primary choice for maintenance in active dependence because it can precipitate severe withdrawal if opioids are still in the system. * **Pethidine (Option B):** This is a short-acting opioid agonist. It is never used for maintenance because its metabolite, **normeperidine**, is neurotoxic and can cause seizures with chronic use. * **L-NAME (Option D):** This is a non-selective inhibitor of Nitric Oxide Synthase (NOS) used primarily in research settings to study vascular resistance; it has no role in treating opioid dependence. **High-Yield Clinical Pearls for NEET-PG:** * **Buprenorphine** (a partial mu-agonist) is another first-line agent for maintenance therapy, often preferred due to a lower risk of fatal overdose (ceiling effect). * **Clonidine** (alpha-2 agonist) is used to manage the *autonomic symptoms* of acute opioid withdrawal (tachycardia, hypertension) but is not used for maintenance. * **Naloxone** is the drug of choice for **acute opioid poisoning**.

Q: Which of the following statements about the mechanism of action of anticonvulsants is false?

Ethosuximide – K+ channel opener. ### Explanation The correct answer is **A (Ethosuximide – K+ channel opener)** because this statement is incorrect. **1. Why Option A is the correct answer (False Statement):** Ethosuximide does not act on potassium channels. Its primary mechanism of action is the **inhibition of T-type Ca²⁺ channels** in thalamic neurons. By reducing these low-threshold calcium currents, it suppresses the rhythmic 3 Hz spike-and-wave discharges characteristic of absence seizures. **2. Analysis of Incorrect Options (True Statements):** * **B. Phenytoin:** Acts by causing **use-dependent blockade of voltage-gated Na⁺ channels**. It prolongs the inactivated state of the channel, preventing high-frequency repetitive firing of action potentials. * **C. Diazepam:** As a Benzodiazepine, it acts as a **GABA-A receptor modulator**. It increases the *frequency* of chloride channel opening in the presence of GABA, leading to hyperpolarization. * **D. Gabapentin:** Although designed as a GABA structural analog, it does not act directly on GABA receptors. It binds to the **α2δ-1 subunit of voltage-gated Ca²⁺ channels**, which indirectly leads to an **increase in GABA release** and a decrease in glutamate release. **3. NEET-PG High-Yield Clinical Pearls:** * **Drug of Choice (DOC):** Ethosuximide is the DOC for **Absence Seizures** (Petit mal). However, if the patient has concomitant Generalized Tonic-Clonic Seizures (GTCS), Valproate is preferred. * **Zero-Order Kinetics:** Phenytoin follows capacity-limited (non-linear) elimination at therapeutic concentrations. * **GABA Mechanism Trick:** Remember **"Ben exerts Frequency, Barbs exert Duration"** (Benzodiazepines increase frequency; Barbiturates increase duration of Cl⁻ channel opening). * **Vigabatrin:** Irreversibly inhibits GABA-transaminase (enzyme that breaks down GABA), leading to increased GABA levels. Watch for visual field defects.

Question 1

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 2

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

Accepted Answer

Sodium valproate

Answer

Carbamazepine

Answer

Phenobarbitone

Answer

Felbamate

Question 3

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 4

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 5

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

Accepted Answer

Mydriasis

Answer

Constipation

Answer

Vomiting

Answer

Analgesia

Question 6

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

Accepted Answer

Renal dysfunction

Answer

Muscle weakness

Answer

Phlebitis

Answer

Respiratory insufficiency

Question 7

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

Question 8

All of the following are true regarding levodopa except?

Accepted Answer

Levodopa cannot cross the blood-brain barrier.

Answer

Half-life of levodopa is 60 to 90 minutes.

Answer

Levodopa can cause orthostatic hypotension and dyskinesias.

Answer

With continued use, the duration of benefit following an individual dose of levodopa becomes progressively shorter.

Question 9

Which of the following drugs is used worldwide for the maintenance therapy of opioid dependence?

Accepted Answer

Methadone

Answer

Naltrexone

Answer

Pethidine

Answer

L-NAME

Question 10

Which of the following statements about the mechanism of action of anticonvulsants is false?

Accepted Answer

Ethosuximide – K+ channel opener

Answer

Phenytoin – Na+ channel blocker

Answer

Diazepam – Facilitates GABA action

Answer

Gabapentin – Increases GABA release

Central Nervous System Pharmacology — MCQs

Central Nervous System Pharmacology — MCQs

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