Central Nervous System Pharmacology Practice Questions

Q: What is the active metabolite of carisoprodol?

Meprobamate. **Explanation:** **Carisoprodol** is a centrally acting skeletal muscle relaxant used for the relief of acute, painful musculoskeletal conditions. Its primary mechanism of action is mediated through its conversion into its active metabolite, **Meprobamate**. 1. **Why Meprobamate is correct:** Carisoprodol is a prodrug. Once ingested, it undergoes extensive hepatic metabolism via the cytochrome P450 enzyme **CYP2C19** to form Meprobamate. Meprobamate itself is an anxiolytic and sedative-hypnotic drug (historically used as a tranquilizer) that acts as a positive allosteric modulator at the **GABA-A receptor**. This metabolite accounts for much of the therapeutic muscle relaxant effect, as well as the drug's potential for abuse and sedation. 2. **Analysis of Incorrect Options:** * **Amphetamine:** This is a CNS stimulant. It is not a metabolite of carisoprodol; however, it is a metabolite of the anti-parkinsonian drug *Selegiline*. * **Doxylamine:** This is a first-generation antihistamine (H1 antagonist) with sedative properties, commonly used as a sleep aid. * **Dimethadione:** This is the active metabolite of the anticonvulsant *Trimethadione*. **NEET-PG High-Yield Pearls:** * **Abuse Potential:** Due to the Meprobamate metabolite, carisoprodol is classified as a Schedule IV controlled substance. It can cause withdrawal symptoms similar to benzodiazepines. * **Pharmacogenomics:** Patients who are "poor metabolizers" of **CYP2C19** will have higher serum levels of carisoprodol and lower levels of meprobamate, altering the drug's efficacy and toxicity profile. * **Other Muscle Relaxants to Remember:** * *Baclofen:* GABA-B agonist. * *Tizanidine:* Alpha-2 agonist. * *Dantrolene:* Acts directly on the Ryanodine receptor (RyR1) in the sarcoplasmic reticulum.

Q: Which condition has seen cannabinoids approved by the USFDA for a new use in June 2018?

Epilepsy. **Explanation:** The correct answer is **Epilepsy**. In June 2018, the USFDA approved **Epidiolex** (a purified form of **Cannabidiol** or CBD) for the treatment of seizures associated with two rare and severe forms of epilepsy: **Lennox-Gastaut syndrome** and **Dravet syndrome**, in patients two years of age and older. This marked the first FDA-approved drug derived from marijuana. **Why the other options are incorrect:** * **Urinary Tract Infection (B):** UTIs are bacterial infections typically treated with antibiotics (e.g., Nitrofurantoin, Fosfomycin). Cannabinoids have no established antimicrobial role in treating acute infections. * **Tuberculosis (C):** TB is caused by *Mycobacterium tuberculosis* and requires a specific regimen of antitubercular drugs (RIPE: Rifampin, Isoniazid, Pyrazinamide, Ethambutol). * **Varicella (D):** Chickenpox is a viral infection caused by the Varicella-Zoster virus. Management involves supportive care or antivirals like Acyclovir; cannabinoids are not indicated. **High-Yield Clinical Pearls for NEET-PG:** * **Mechanism:** Unlike THC, Cannabidiol (CBD) does not produce a "high" (non-psychoactive). Its anticonvulsant effect is thought to involve the modulation of intracellular calcium and adenosine signaling, rather than direct action on CB1/CB2 receptors. * **Other FDA-approved Cannabinoids:** **Dronabinol** and **Nabilone** are synthetic cannabinoids used for chemotherapy-induced nausea and vomiting (CINV) and anorexia associated with weight loss in AIDS patients. * **Side Effects:** Common side effects of Epidiolex include somnolence, decreased appetite, diarrhea, and potential elevation of liver enzymes (transaminases).

Q: Which of the following drugs is used for the prophylaxis of migraine but not for angina pectoris?

Flunarizine. **Explanation:** The correct answer is **Flunarizine**. **1. Why Flunarizine is Correct:** Flunarizine is a **non-selective calcium channel blocker (CCB)** that also possesses H1-antihistaminic, dopamine D2 blocking, and sodium channel blocking properties. Unlike conventional CCBs, it is highly lipophilic and crosses the blood-brain barrier, acting primarily on the CNS. It is specifically indicated for the **prophylaxis of migraine** and vertigo. However, it has **no significant effect on systemic vascular resistance or myocardial oxygen demand**, making it ineffective for the treatment or prophylaxis of angina pectoris. **2. Why the Other Options are Incorrect:** * **Verapamil & Diltiazem (Options A & B):** These are non-dihydropyridine CCBs. They have significant negative inotropic and chronotropic effects on the heart and cause peripheral vasodilation. They are first-line agents for **angina pectoris** [1], [2]. Verapamil is also used off-label for migraine prophylaxis (though less commonly than beta-blockers), but since it is used for both, it does not fit the question's criteria. * **Amlodipine (Option D):** This is a dihydropyridine CCB used extensively for hypertension and **chronic stable/vasospastic angina** [1]. It has no established role in migraine prophylaxis. **3. High-Yield Clinical Pearls for NEET-PG:** * **Side Effects of Flunarizine:** Due to its D2-blocking activity, it can cause **Extrapyramidal Symptoms (EPS)** and **Parkinsonism**, especially in the elderly. It is also known to cause significant weight gain and sedation. * **Drug of Choice (DOC):** While Flunarizine is used, **Propranolol** remains the DOC for migraine prophylaxis [3]. * **Mechanism in Migraine:** Flunarizine prevents intracellular calcium overload during the cortical spreading depression phase of a migraine attack.

Q: For which of the following seizures would Carbamazepine be prescribed as the appropriate drug treatment for prevention?

Complex partial. **Explanation:** **Carbamazepine (CBZ)** is a first-line antiepileptic drug primarily used for the management of focal (partial) seizures. Its mechanism of action involves the **blockade of voltage-gated sodium channels** in their inactivated state, which prevents high-frequency repetitive firing of action potentials. 1. **Why Complex Partial is Correct:** Carbamazepine is considered a drug of choice for both **Simple and Complex Partial seizures**, as well as Generalized Tonic-Clonic Seizures (GTCS). In clinical practice and exam scenarios, it is highly associated with the management of complex partial seizures due to its efficacy and established safety profile for focal epilepsy. 2. **Why other options are incorrect:** * **Generalized Tonic-Clonic (A):** While CBZ is effective for GTCS, it is often secondary to Valproate (which covers a broader spectrum) or Levetiracetam. * **Simple Partial (B):** CBZ is used here, but "Complex Partial" is the more classic association for this specific question type. * **Status Epilepticus (C):** This is a medical emergency requiring rapid-acting intravenous drugs. The drugs of choice are **Lorazepam/Diazepam** (to stop the seizure) followed by **Fosphenytoin/Phenytoin** (for maintenance). CBZ is not used here as it lacks an IV formulation and has a slow onset. **High-Yield Clinical Pearls for NEET-PG:** * **Drug of Choice:** Carbamazepine is the DOC for **Trigeminal Neuralgia**. * **Side Effects:** It is a potent **enzyme inducer** (CYP3A4). Watch for **Diplopia** (earliest sign of toxicity), **SIADH** (hyponatremia), and **Stevens-Johnson Syndrome** (especially in patients with HLA-B*1502 allele). * **Contraindication:** CBZ **exacerbates Absence and Myoclonic seizures**; never use it if these are suspected.

Q: All of the following are properties of local anesthetics EXCEPT:

Preferential binding to resting channels. ### Explanation Local anesthetics (LAs) act primarily by inhibiting the influx of sodium ions through **voltage-gated Na+ channels** in the neuronal cell membrane. **Why Option B is correct:** Local anesthetics exhibit **"state-dependent blockade."** They have a higher affinity for channels in the **activated (open)** or **inactivated** states rather than the **resting** state. This is because the binding site for LAs is located on the internal (cytoplasmic) side of the channel, which becomes more accessible when the channel is open. This phenomenon is also known as **use-dependent** or **frequency-dependent blockade**, meaning nerves with higher firing frequencies (e.g., pain fibers) are blocked more rapidly. **Why other options are incorrect:** * **Option A:** This is the primary mechanism of action. LAs bind to the alpha-subunit of voltage-gated Na+ channels, preventing sodium influx. * **Option C:** By blocking Na+ channels, LAs decrease the rate of depolarization, which leads to a **slowing of axonal impulse conduction** and a decrease in the amplitude of the action potential. * **Option D:** LAs prolong the time the channel remains in the inactivated state, thereby **increasing the refractory period** of the nerve membrane, making it impossible for another action potential to be generated immediately. ### High-Yield NEET-PG Pearls: * **Order of Blockade:** Autonomic > Pain (C & Aδ) > Temperature > Touch > Pressure > Motor. * **Sensitivity:** Small, myelinated fibers are generally blocked more easily than large, unmyelinated fibers. * **pH Effect:** LAs are weak bases. In **acidic environments (e.g., infected tissue)**, they become ionized and cannot cross the lipid membrane, leading to **reduced efficacy**. * **Bupivacaine:** Most cardiotoxic LA; managed with **20% Intralipid** (Lipid rescue).

Q: All of the following are approved for the treatment of relapsing-remitting multiple sclerosis (RRMS) subtype, except?

Mycophenolate. **Explanation:** The correct answer is **D. Mycophenolate**. Multiple Sclerosis (MS) is a chronic autoimmune demyelinating disease of the CNS. Treatment is divided into managing acute relapses (Corticosteroids) and **Disease-Modifying Therapies (DMTs)** to reduce the frequency of relapses in the Relapsing-Remitting (RRMS) subtype. **Why Mycophenolate is the correct answer:** While Mycophenolate mofetil is a potent immunosuppressant used in organ transplantation and certain autoimmune conditions (like Lupus Nephritis), it is **not FDA-approved** for the treatment of RRMS. It is occasionally used "off-label" in refractory cases, but it does not hold a standard indication for MS. **Analysis of Incorrect Options:** * **Interferon beta-1a & 1b:** These were the first first-line DMTs approved for RRMS. They work by modulating the immune response, reducing T-cell proliferation, and decreasing the passage of inflammatory cells across the blood-brain barrier. * **Glatiramer Acetate:** This is a synthetic polypeptide mixture that mimics **Myelin Basic Protein**. It acts as a "decoy," diverting the autoimmune attack away from the patient's myelin. It is a standard first-line injectable therapy for RRMS. **High-Yield Clinical Pearls for NEET-PG:** * **Drug of Choice for Acute Relapse:** Intravenous Methylprednisolone. * **Oral DMTs for RRMS:** Fingolimod (S1P modulator), Teriflunomide (DHODH inhibitor), and Dimethyl fumarate. * **Monoclonal Antibodies:** Natalizumab (targets α4β1-integrin; risk of PML) and Ocrelizumab (targets CD20; approved for Primary Progressive MS). * **Glatiramer Safety:** It is often considered the safest DMT during pregnancy.

Q: Gum hypertrophy is an adverse effect of which of the following drugs when used at therapeutic levels?

Phenytoin. **Explanation:** **Phenytoin** is a classic cause of **Gingival Hyperplasia (Gum Hypertrophy)**, occurring in approximately 30–50% of patients. The underlying mechanism involves the drug’s effect on calcium metabolism and the stimulation of **platelet-derived growth factor (PDGF)**. This leads to the over-proliferation of gingival fibroblasts and increased collagen synthesis. Poor oral hygiene is a significant risk factor, and the condition often regresses upon drug discontinuation. **Analysis of Incorrect Options:** * **Phenobarbitone:** Primarily causes sedation, cognitive impairment, and skin rashes. It does not typically affect the gums. * **Carbamazepine:** Common side effects include diplopia, ataxia, and hyponatremia (SIADH). It is notably "gingival-neutral." * **Sodium Valproate:** Known for causing weight gain, alopecia (curly hair regrowth), hepatotoxicity, and pancreatitis. While it can cause transient thrombocytopenia, it does not cause gum hypertrophy. **High-Yield Clinical Pearls for NEET-PG:** * **Other Drugs causing Gingival Hyperplasia:** Remember the mnemonic **"PNC"** — **P**henytoin, **N**ifedipine (and other Calcium Channel Blockers like Verapamil/Amlodipine), and **C**yclosporine. * **Phenytoin Side Effects Mnemonic (HOT MALAYALAM):** **H**irsutism, **O**steomalacia, **T**eratogenicity (Fetal Hydantoin Syndrome), **M**egaloblastic anemia, **A**taxia, **L**ymphadenopathy, **A**rrhythmias, **Y**ellow-brown skin, **A**denopathy, **L**eukopenia, **A**nd **M**outh (Gingival Hyperplasia). * **Zero-Order Kinetics:** Phenytoin follows capacity-limited elimination at therapeutic/high doses, making its plasma concentration unpredictable.

Q: Which of the following local anesthetics exhibits significant extrahepatic metabolism?

Prilocaine. **Explanation:** Local anesthetics (LAs) are classified into esters and amides. While esters are metabolized by plasma pseudocholinesterases, **amides** are primarily metabolized by hepatic microsomal enzymes (CYP450). **Why Prilocaine is correct:** Prilocaine is an amide local anesthetic that is unique because it undergoes significant **extrahepatic metabolism**. While it is metabolized in the liver, a substantial portion is also metabolized in the **kidneys and lungs**. A specific metabolite of prilocaine, **o-toluidine**, is clinically significant as it can oxidize hemoglobin to methemoglobin, leading to **methemoglobinemia** (a high-yield side effect). **Why the other options are incorrect:** * **Lignocaine (Lidocaine):** The prototype amide LA. It is almost exclusively metabolized in the liver via oxidative dealkylation. It has a rapid onset but lacks significant extrahepatic clearance. * **Bupivacaine:** A long-acting amide LA. It is metabolized strictly by the liver. It is notably more cardiotoxic than other LAs due to its slow dissociation from cardiac sodium channels. * **Ropivacaine:** An S-enantiomer of bupivacaine with a similar metabolic profile (purely hepatic). It is preferred over bupivacaine for its reduced cardiotoxicity and greater sensory-motor dissociation. **High-Yield NEET-PG Pearls:** 1. **Methemoglobinemia:** Associated with **Prilocaine** and **Benzocaine**. The treatment of choice is **Methylene Blue**. 2. **Shortest acting Amide:** Lidocaine. 3. **Longest acting Amide:** Bupivacaine/Ropivacaine. 4. **Rule of Thumb:** Amide LAs have two "i"s in their name (L**i**doca**i**ne, Pr**i**loca**i**ne), while esters have only one (Proca**i**ne).

Q: Naloxone is contraindicated in neonatal resuscitation if the mother is on which of the following substances?

Methadone. The correct answer is **Methadone**. **Mechanism and Rationale:** Naloxone is a competitive opioid antagonist used to reverse respiratory depression. However, it is strictly contraindicated in neonates born to mothers with **chronic opioid dependence** (e.g., Methadone or Heroin maintenance). In these infants, the drug crosses the placenta, leading to physical dependence in utero [1]. Administering Naloxone triggers **acute, severe withdrawal syndrome**, which can manifest as intractable seizures, cardiovascular collapse, and extreme irritability [2]. In neonatal resuscitation, the preferred management for opioid-induced respiratory depression is **positive pressure ventilation (PPV)** rather than pharmacological reversal. **Analysis of Options:** * **Methadone (Correct):** As a long-acting opioid used in maintenance therapy, it causes significant fetal physical dependence. Naloxone administration precipitates immediate withdrawal [1]. * **Heroin:** While also an opioid, Methadone is the more "classic" board exam answer associated with chronic maternal addiction programs. However, Naloxone is contraindicated for *any* chronic opioid exposure (including Heroin) [1]. * **Cocaine & Amphetamine:** These are CNS stimulants, not opioids. Naloxone has no pharmacological effect on stimulant-induced toxicity or withdrawal; therefore, it is neither indicated nor specifically contraindicated in the context of neonatal withdrawal for these substances. **NEET-PG High-Yield Pearls:** * **Drug of Choice for Opioid Overdose:** Naloxone (IV/Intranasal). * **Duration of Action:** Naloxone has a short half-life (30–90 mins); patients must be monitored for "re-narcotization" as the opioid may outlast the antagonist. * **Naltrexone vs. Naloxone:** Naltrexone is orally active with a long half-life, used for alcohol and opioid de-addiction, not acute reversal. * **Neonatal Resuscitation Protocol:** Always prioritize airway and ventilation over Naloxone.

Question 1

What is the active metabolite of carisoprodol?

Accepted Answer

Meprobamate

Answer

Amphetamine

Answer

Doxylamine

Answer

Dimethadione

Question 2

Which condition has seen cannabinoids approved by the USFDA for a new use in June 2018?

Accepted Answer

Epilepsy

Answer

Urinary Tract Infection

Answer

Tuberculosis

Answer

Varicella (Chicken Pox)

Question 3

Which of the following drugs is used for the prophylaxis of migraine but not for angina pectoris?

Accepted Answer

Flunarizine

Answer

Verapamil

Answer

Diltiazem

Answer

Amlodipine

Question 4

For which of the following seizures would Carbamazepine be prescribed as the appropriate drug treatment for prevention?

Accepted Answer

Complex partial

Answer

Generalized tonic clonic

Answer

Simple partial

Answer

Status epilepticus

Question 5

All of the following are properties of local anesthetics EXCEPT:

Accepted Answer

Preferential binding to resting channels

Answer

Blockade of voltage-dependent Na+ channels

Answer

Slowing of axonal impulse conduction

Answer

Increase in the membrane refractory period

Question 6

All of the following are approved for the treatment of relapsing-remitting multiple sclerosis (RRMS) subtype, except?

Accepted Answer

Mycophenolate

Answer

Interferon beta-1a

Answer

Interferon beta-1b

Answer

Glatiramer

Question 7

Gum hypertrophy is an adverse effect of which of the following drugs when used at therapeutic levels?

Accepted Answer

Phenytoin

Answer

Phenobarbitone

Answer

Carbamazepine

Answer

Sodium valproate

Question 8

Which of the following statements is true about local anesthetics?

Accepted Answer

Dibucaine is the drug of choice for epidural anesthesia.

Answer

Cocaine acts by decreasing norepinephrine reuptake.

Answer

Local anesthetics act by decreasing sodium entry into the nerve cell.

Answer

Lignocaine is an amide-type local anesthetic.

Question 9

Which of the following local anesthetics exhibits significant extrahepatic metabolism?

Accepted Answer

Prilocaine

Answer

Lignocaine

Answer

Bupivacaine

Answer

Ropivacaine

Question 10

Naloxone is contraindicated in neonatal resuscitation if the mother is on which of the following substances?

Accepted Answer

Methadone

Answer

Cocaine

Answer

Amphetamine

Answer

Heroin

Central Nervous System Pharmacology — MCQs

Central Nervous System Pharmacology — MCQs

On this page

Practice by Chapter

Want unlimited practice?