Central Nervous System Pharmacology Practice Questions

Q: Which drug requires visual field monitoring before starting treatment?

Vigabatrin. **Explanation:** **Vigabatrin (Option A)** is the correct answer because it is associated with a high risk of **permanent bilateral concentric visual field constriction** (peripheral vision loss). This occurs in approximately 30–50% of patients due to the accumulation of GABA in the retina, leading to retinal toxicity. Consequently, baseline visual field testing (perimetry) is mandatory before initiation, followed by monitoring every 6 months. **Why the other options are incorrect:** * **Topiramate (Option B):** While it can cause ocular side effects like acute myopia and secondary angle-closure glaucoma, it does not typically require routine visual field monitoring. Its most high-yield side effects are nephrolithiasis and cognitive "fogging." * **Valproic acid (Option C):** Primarily associated with hepatotoxicity, pancreatitis, and neural tube defects. It does not have significant ocular toxicity. * **Carbamazepine (Option D):** Known for causing diplopia and ataxia as dose-related side effects, but it does not cause permanent visual field defects requiring screening. **Clinical Pearls for NEET-PG:** * **Mechanism of Action:** Vigabatrin is an irreversible inhibitor of **GABA-transaminase**, the enzyme responsible for GABA degradation. * **Drug of Choice:** It is the first-line treatment for **Infantile Spasms** (West Syndrome) associated with Tuberous Sclerosis. * **Mnemonic:** **Vi**gabatrin = **Vi**sual field loss (**Vi**-**Ga**-**B**atrin: **Vi**sual **Ga**ba **B**locker). * **Black Box Warning:** Due to the risk of permanent vision loss, it is often restricted to patients who have failed other treatments.

Q: Which of the following opioids is used via the transdermal route for malignancy-associated pain?

Fentanyl. **Explanation:** **Fentanyl** is the correct answer because it possesses the specific physicochemical properties required for effective transdermal delivery: **high lipid solubility** and **low molecular weight**. These characteristics allow it to penetrate the stratum corneum easily. In malignancy-associated chronic pain, the Fentanyl transdermal patch (Durogesic) provides a stable plasma concentration over 72 hours, offering a non-invasive alternative for patients with dysphagia or persistent nausea. **Why the other options are incorrect:** * **Morphine:** It is the gold standard for cancer pain (WHO Step 3) but is **hydrophilic**. Its poor lipid solubility makes it unsuitable for transdermal absorption; it is primarily administered orally or intravenously. * **Codeine:** A weak opioid (WHO Step 2) used for mild-to-moderate pain. It is a prodrug converted to morphine and is administered orally. * **Oxycodone:** A potent semi-synthetic opioid used for severe pain. While available in controlled-release oral formulations, it is not standardly used via the transdermal route. **High-Yield Clinical Pearls for NEET-PG:** * **Buprenorphine** is the only other opioid commonly used via a transdermal patch in clinical practice. * **Fentanyl Patch Timing:** It takes **12–24 hours** to reach peak plasma concentration; therefore, it is used for *chronic* stable pain, never for *acute* or breakthrough pain. * **Potency:** Fentanyl is approximately **75–100 times more potent** than Morphine. * **Safety:** Fentanyl is preferred over Morphine in patients with **renal failure** as it has no active metabolites (unlike Morphine-6-glucuronide).

Q: A 75-year-old male patient, started on new medications for Parkinson's disease, has begun gambling and making inappropriate sexual comments. Which medication is likely responsible for this change in behavior?

Ropinirole. **Explanation:** The patient is presenting with **Impulse Control Disorders (ICDs)**, characterized by behaviors such as pathological gambling, hypersexuality, compulsive shopping, and binge eating. **Why Ropinirole is correct:** Ropinirole is a **non-ergot Dopamine Agonist (DA)**. These agents have a high affinity for **D3 receptors**, which are primarily located in the **mesolimbic system** (the brain's reward pathway). Excessive stimulation of these receptors leads to behavioral disinhibition and the development of ICDs. While all dopamine-enhancing drugs can theoretically cause these side effects, non-ergot DAs (Ropinirole and Pramipexole) carry the highest risk, occurring in up to 14–17% of patients. **Analysis of Incorrect Options:** * **Levodopa + Carbidopa:** While Levodopa can cause ICDs (often termed "Dopamine Dysregulation Syndrome"), the risk is significantly lower than with dopamine agonists. It is more commonly associated with motor fluctuations and dyskinesias. * **Bromocriptine:** This is an ergot-derived dopamine agonist. While it can cause ICDs, it is less commonly used today due to risks of pulmonary and cardiac fibrosis, and its D3 selectivity is less pronounced than that of Ropinirole. * **Entacapone:** This is a COMT inhibitor used to prevent the peripheral breakdown of Levodopa. It does not directly stimulate dopamine receptors and is not a primary cause of ICDs. **High-Yield Clinical Pearls for NEET-PG:** * **D3 Receptors = Reward/Emotion:** Think "D3 for Desire." * **Management:** The first step in managing ICDs in Parkinson’s is to **taper and discontinue the Dopamine Agonist.** * **Pramipexole vs. Ropinirole:** Both are high-yield triggers for ICDs in exam questions. * **Risk Factors:** Younger age, male gender, and a pre-existing history of impulsive behavior or substance use.

Q: All of the following are Glutamate receptors except?

AMDA receptors. **Explanation:**Glutamate is the primary excitatory neurotransmitter in the Central Nervous System (CNS) [2]. Its receptors are broadly classified into two categories: **Ionotropic** (ligand-gated ion channels) and **Metabotropic** (G-protein coupled receptors) [1, 2].1. **Why Option C is Correct:** **AMDA receptors** do not exist in medical pharmacology. This is a distractor term often confused with AMPA. The correct acronyms for ionotropic glutamate receptors are NMDA, AMPA, and Kainate [1, 2].2. **Analysis of Incorrect Options:** * **AMPA (α-amino-3-hydroxy-5-methyl-4-isoxazolepropionic acid):** These are ionotropic receptors responsible for fast excitatory synaptic transmission. They primarily allow the influx of $Na^+$ and efflux of $K^+$ [1, 2]. * **NMDA (N-methyl-D-aspartate):** These are unique voltage-dependent ionotropic receptors [2]. At resting membrane potential, they are blocked by **Magnesium ($Mg^{2+}$)** ions. They are highly permeable to $Ca^{2+}$ and play a crucial role in long-term potentiation (memory) [1]. * **Kainate Receptors:** These are found in the hippocampus and cerebellum; they function similarly to AMPA receptors but are less common [1, 2].**High-Yield Clinical Pearls for NEET-PG:** * **Excitotoxicity:** Excessive glutamate stimulation leads to neuronal death (seen in stroke and Alzheimer’s) due to massive $Ca^{2+}$ influx via NMDA receptors [1].* **Memantine:** An NMDA receptor antagonist used in the treatment of moderate-to-severe Alzheimer’s disease [1].* **Ketamine & Phencyclidine (PCP):** These act as non-competitive antagonists at the NMDA receptor [1].* **Ketamine** is often used as a dissociative anesthetic [1].

Q: Which of the following is NOT used in the management of painful diabetic neuropathy?

Dextroamphetamine. **Explanation:** The management of painful diabetic neuropathy focuses on modulating neurotransmitters involved in pain signaling (Serotonin, Norepinephrine, and GABA) or blocking sodium channels. **Why Dextroamphetamine is the correct answer:** Dextroamphetamine is a central nervous system (CNS) stimulant primarily used for ADHD and narcolepsy. It has **no established role** in the clinical management of neuropathic pain. While it increases synaptic dopamine and norepinephrine, it does not provide the peripheral or spinal cord analgesia required for diabetic neuropathy and carries a high risk of addiction and cardiovascular side effects. **Analysis of other options:** * **Amitriptyline:** A Tricyclic Antidepressant (TCA) and often the **first-line agent**. It inhibits the reuptake of serotonin and norepinephrine, enhancing descending inhibitory pain pathways. * **Phenytoin:** An antiepileptic that acts as a sodium channel blocker. While newer agents like Pregabalin or Gabapentin are now preferred, Phenytoin was historically used to stabilize neuronal membranes and reduce ectopic discharges in painful neuropathy. * **Local use of Capsicum (Capsaicin):** Derived from chili peppers, topical capsaicin cream desensitizes nociceptors by depleting **Substance P** from peripheral sensory neurons. **NEET-PG High-Yield Pearls:** * **First-line drugs:** Pregabalin (Calcium channel α2-δ ligand), Duloxetine (SNRI), or Amitriptyline (TCA). * **FDA-approved specifically for DPNP:** Pregabalin and Duloxetine. * **Topical therapy:** Capsaicin cream or Lidocaine patches are useful for localized symptoms. * **Mechanism of TCAs:** Inhibition of norepinephrine and serotonin reuptake + Sodium channel blockade.

Q: All of the following statements about the treatment of migraine are true, except:

Sumatriptan is used for chronic migraine.. **Explanation:** The correct answer is **D** because **Sumatriptan is used for the acute management of migraine attacks**, not for chronic migraine prophylaxis. **1. Why Option D is the correct (incorrect statement):** In pharmacology, migraine treatment is divided into **Abortive (Acute)** and **Prophylactic (Chronic)** therapy. Sumatriptan (and other triptans) are potent vasoconstrictors used to terminate an ongoing attack. Chronic migraine (defined as ≥15 headache days/month) requires prophylactic agents like Topiramate, Propranolol, Amitriptyline, or Flunarizine to reduce frequency. Using triptans too frequently for chronic migraine can actually lead to **Medication Overuse Headache (MOH)**. **2. Analysis of other options:** * **Option A:** Narotriptan has higher oral bioavailability and a longer half-life (~6 hours) compared to Sumatriptan (~2 hours), leading to a slower onset but lower recurrence rates. * **Option B:** Rizatriptan (10mg) has been shown in clinical trials to have slightly higher efficacy and faster onset than the standard 50mg/100mg dose of Sumatriptan. * **Option C:** Triptans are selective agonists at **5-HT 1B** (causing cranial vasoconstriction) and **5-HT 1D** (inhibiting neuropeptide release from trigeminal nerves) receptors. **NEET-PG High-Yield Pearls:** * **Drug of Choice (DOC) for Acute Severe Migraine:** Sumatriptan (Subcutaneous is fastest). * **DOC for Prophylaxis:** Propranolol (Beta-blocker). * **Contraindication:** Triptans are contraindicated in patients with **Ischemic Heart Disease (IHD)** or Prinzmetal angina due to coronary vasoconstriction. * **Newer Agents:** **Lasmiditan** (5-HT 1F agonist) is used for patients with cardiovascular risks as it does not cause vasoconstriction.

Q: A 25-year-old woman with myoclonic seizures is well controlled on valproate. She indicates that she is interested in conceiving in the next year. With respect to her antiepileptic medication, what should be considered?

Switch to lamotrigine. ### Explanation **1. Why the correct answer is right:** Sodium Valproate is highly effective for generalized epilepsies (including myoclonic seizures), but it is the most **teratogenic** antiepileptic drug (AED). It is associated with a high risk of **neural tube defects** (e.g., spina bifida), craniofacial abnormalities, and impaired cognitive development in the offspring. In a woman planning pregnancy, the goal is to switch to an AED with a lower teratogenic profile before conception [1]. **Lamotrigine** and Levetiracetam are considered the safest alternatives during pregnancy, as they carry the lowest risk of major congenital malformations. **2. Why the incorrect options are wrong:** * **Option A:** Continuing Valproate is contraindicated in a woman planning pregnancy unless all other options have failed, due to the significant risk of physical and neurodevelopmental defects. * **Option C:** While the risk of teratogenicity is dose-dependent (higher risk >1000 mg/day), there is no "safe" dose of Valproate that eliminates the risk. Switching to a safer drug is preferred over merely reducing the dose of a known teratogen. **3. Clinical Pearls for NEET-PG:** * **Valproate & Pregnancy:** Causes neural tube defects by interfering with folate metabolism. Supplementation with **high-dose Folic Acid (5 mg/day)** is mandatory if Valproate must be used. * **Drug of Choice (DOC):** Valproate is the DOC for myoclonic seizures in non-pregnant patients. However, in pregnancy, Lamotrigine or Levetiracetam are preferred. * **Phenytoin/Carbamazepine:** These cause **Fetal Hydantoin Syndrome** (cleft lip/palate, digital hypoplasia). * **Management Tip:** Always switch medications *before* conception to ensure seizure control is maintained on the new agent, as switching during pregnancy increases the risk of breakthrough seizures and status epilepticus.

Q: Lofexidine has been approved recently for the withdrawal of which substance?

Morphine. **Explanation:** **Lofexidine** is a selective **alpha-2 adrenergic receptor agonist**. It was recently approved (FDA approval in 2018) specifically for the management of **opioid withdrawal symptoms** (such as those from Morphine, Heroin, or Methadone). **Why Morphine is Correct:** During opioid withdrawal, there is a massive surge in norepinephrine release from the *locus coeruleus*. This leads to autonomic hyperactivity (tachycardia, hypertension, sweating, and anxiety). Lofexidine binds to presynaptic alpha-2 receptors, inhibiting the release of norepinephrine. While it does not treat the underlying craving, it significantly reduces the physical symptoms of withdrawal. It is preferred over its predecessor, **Clonidine**, because it has a lower risk of causing profound hypotension. **Why Other Options are Incorrect:** * **Alcohol:** Withdrawal is managed primarily with Benzodiazepines (e.g., Diazepam, Chlordiazepoxide) to prevent seizures and delirium tremens. * **Cocaine:** There is no FDA-approved pharmacological treatment for cocaine withdrawal; management is primarily supportive and behavioral. * **Cannabis:** Withdrawal is usually mild and managed with supportive care or occasionally Gabapentin/Quetiapine off-label; alpha-2 agonists have no role here. **High-Yield Clinical Pearls for NEET-PG:** * **Lofexidine vs. Clonidine:** Lofexidine is more selective for alpha-2A receptors, making it safer regarding blood pressure changes. * **Non-Opioid Status:** Unlike Methadone or Buprenorphine, Lofexidine is **not** an opioid and has no abuse potential. * **Locus Coeruleus:** Remember this as the primary site of noradrenergic hyperactivity during opioid withdrawal. * **Side Effects:** Monitor for bradycardia, hypotension, and QT prolongation.

Q: Methadone is used in the management of opioid addiction because:

It is longer acting and causes milder withdrawal symptoms. **Explanation:** Methadone is a synthetic, long-acting **full μ-opioid receptor agonist**. Its utility in opioid de-addiction (Maintenance Therapy) stems from its unique pharmacokinetic profile. **Why Option D is Correct:** Methadone has a significantly longer half-life (24–36 hours) compared to morphine or heroin. Because of this slow elimination, the decline in plasma concentration is gradual, leading to **milder, though more prolonged, withdrawal symptoms**. Furthermore, its slow onset of action when taken orally prevents the "rush" or euphoria associated with intravenous heroin, helping to stabilize the patient and reduce drug-seeking behavior. **Why Other Options are Incorrect:** * **Option A:** Methadone is a potent analgesic. Its analgesic potency is roughly equal to or greater than morphine; this is not the reason it is used for addiction. * **Option B:** Methadone is a full **agonist**, not an antagonist. Naloxone and Naltrexone are examples of opioid antagonists. * **Option C:** Methadone is an opioid and has significant **addictive potential**. However, it is used to replace a "dangerous" addiction (heroin) with a "controlled" addiction under medical supervision. **High-Yield Clinical Pearls for NEET-PG:** * **NMDA Antagonism:** Besides μ-receptors, Methadone also antagonizes NMDA receptors, which may help in treating neuropathic pain and reducing opioid tolerance. * **ECG Monitoring:** A critical side effect of Methadone is **QT interval prolongation**, which can lead to *Torsades de Pointes*. * **Levomethadyl acetate (LAAM):** A related drug with an even longer half-life (72–96 hours), allowing for dosing every 2–3 days. * **Buprenorphine:** Often preferred over methadone for office-based treatment as it is a **partial agonist** with a lower risk of fatal overdose (ceiling effect).

Q: Which of the following serotonergic receptors functions as an autoreceptor?

5-HT1a. ### Explanation **Correct Option: A (5-HT1A)** In the central nervous system, **autoreceptors** are receptors located on the presynaptic neuron that provide negative feedback, inhibiting the further release or firing of that specific neurotransmitter. * **5-HT1A** receptors function as **somatodendritic autoreceptors** primarily located in the **Raphe nuclei**. When stimulated, they decrease the firing rate of serotonergic neurons, thereby reducing the overall release of serotonin (5-HT). This is a high-yield concept in the mechanism of action of SSRIs, where chronic stimulation leads to the downregulation of these autoreceptors, eventually increasing serotonin levels in the synapse. **Analysis of Incorrect Options:** * **B. 5-HT1B/1D:** While these are also inhibitory, they are primarily **terminal autoreceptors** (located on the axon terminals) rather than somatodendritic. While technically autoreceptors, 5-HT1A is the classic "textbook" answer for somatodendritic feedback in the Raphe nuclei. (Note: 5-HT1D is the target for Triptans in migraine). * **C. 5-HT2A:** These are **postsynaptic** excitatory receptors coupled to the Gq protein. They are the primary targets for atypical antipsychotics (antagonism) and hallucinogens like LSD (agonism). * **D. 5-HT:** This is the neurotransmitter itself (Serotonin), not a specific receptor subtype. **NEET-PG High-Yield Pearls:** 1. **Buspirone:** A selective **5-HT1A partial agonist** used as a non-benzodiazepine anxiolytic (takes 2 weeks to work). 2. **All 5-HT receptors are G-protein coupled (GPCRs) EXCEPT 5-HT3**, which is a ligand-gated ion channel (target for Ondansetron). 3. **5-HT4 agonists** (e.g., Prucalopride) are used as prokinetics in chronic constipation. 4. **5-HT2C antagonism** is associated with weight gain in patients taking atypical antipsychotics like Clozapine.

Question 1

Which drug requires visual field monitoring before starting treatment?

Accepted Answer

Vigabatrin

Answer

Topiramate

Answer

Valproic acid

Answer

Carbamazepine

Question 2

Which of the following opioids is used via the transdermal route for malignancy-associated pain?

Accepted Answer

Fentanyl

Answer

Morphine

Answer

Codeine

Answer

Oxycodone

Question 3

A 75-year-old male patient, started on new medications for Parkinson's disease, has begun gambling and making inappropriate sexual comments. Which medication is likely responsible for this change in behavior?

Accepted Answer

Ropinirole

Answer

Levodopa + Carbidopa

Answer

Bromocriptine

Answer

Entacapone

Question 4

All of the following are Glutamate receptors except?

Accepted Answer

AMDA receptors

Answer

Kainate receptors

Answer

NMDA receptors

Answer

AMPA receptors

Question 5

Which of the following is NOT used in the management of painful diabetic neuropathy?

Accepted Answer

Dextroamphetamine

Answer

Phenytoin

Answer

Local use of capsicum

Answer

Amitriptyline

Question 6

All of the following statements about the treatment of migraine are true, except:

Accepted Answer

Sumatriptan is used for chronic migraine.

Answer

Narotriptan has a slower onset and longer half-life than sumatriptan.

Answer

Rizatriptan is more efficacious than sumatriptan.

Answer

Sumatriptan is a selective 5-HT 1B/1D agonist.

Question 7

A 25-year-old woman with myoclonic seizures is well controlled on valproate. She indicates that she is interested in conceiving in the next year. With respect to her antiepileptic medication, what should be considered?

Accepted Answer

Switch to lamotrigine

Answer

Leave her on current therapy

Answer

Decrease valproate dose

Answer

None of the above

Question 8

Lofexidine has been approved recently for the withdrawal of which substance?

Accepted Answer

Morphine

Answer

Alcohol

Answer

Cocaine

Answer

Cannabis

Question 9

Methadone is used in the management of opioid addiction because:

Accepted Answer

It is longer acting and causes milder withdrawal symptoms

Answer

Its analgesic activity is less than that of morphine

Answer

It is an opioid receptor antagonist

Answer

It is not addictive

Question 10

Which of the following serotonergic receptors functions as an autoreceptor?

Accepted Answer

5-HT1a

Answer

5-HT1B/1D

Answer

5-HT2a

Answer

5-HT

Central Nervous System Pharmacology — MCQs

Central Nervous System Pharmacology — MCQs

On this page

Practice by Chapter

Want unlimited practice?