Central Nervous System Pharmacology Practice Questions

Q: Which of the following is used for the patient on antiparkinsonian medication levodopa + carbidopa, but patient showing marked on-off effect?

Selegiline. ***Selegiline*** - **Selegiline** is a **MAO-B inhibitor** that slows the breakdown of dopamine in the brain, thus extending the therapeutic effect of **levodopa** and reducing motor fluctuations including "on-off" phenomena. - It works by inhibiting the enzyme monoamine oxidase type B, which metabolizes dopamine, thereby preserving both endogenous and levodopa-derived dopamine for more sustained dopaminergic stimulation. - **MAO-B inhibitors** are established adjuncts to levodopa therapy for managing motor complications and reducing "off" time. *Bromocriptine* - **Bromocriptine** is a **dopamine agonist** that directly stimulates dopamine receptors (particularly D2 receptors) and has a longer half-life than levodopa, providing more continuous dopaminergic stimulation [1]. - While dopamine agonists are also effective for motor fluctuations, **Selegiline** is often preferred as an initial adjunct due to its better tolerability profile and lower risk of inducing dyskinesias. - Bromocriptine can cause more side effects including **dyskinesias**, **hallucinations**, and **nausea**, particularly in elderly patients [1]. *Amantadine* - **Amantadine** is an **NMDA receptor antagonist** primarily used to treat **levodopa-induced dyskinesia** rather than motor fluctuations. - While it has mild antiparkinsonian effects, it is not the preferred agent for managing "on-off" phenomena specifically. - Its mechanism does not directly prolong levodopa's effect or prevent dopamine breakdown. *Rimonabant* - **Rimonabant** is a **cannabinoid receptor 1 (CB1) antagonist** that was previously marketed for obesity and smoking cessation but was **withdrawn from the market** due to serious psychiatric adverse effects including depression and suicidality. - It has **no role** in the management of **Parkinson's disease** or its motor complications.

Q: All of the following about thiopentone are true except which one?

IV injection is painless. ***IV injection is painless*** - Thiopentone is a **barbiturate anesthetic** that is known to cause **pain on injection** due to its **alkaline pH** and propensity to cause local irritation. - This characteristic makes the statement that its IV injection is painless incorrect, as pain and venous irritation are common side effects. *It decreases ICP* - Thiopentone, like other barbiturates, causes **cerebral vasoconstriction**, leading to a decrease in **cerebral blood flow** and **intracranial pressure (ICP)**, making it useful in neurosurgical settings. - This effect is due to a reduction in **cerebral metabolic rate for oxygen (CMRO2)**, which couples with cerebral blood flow. *It has anticonvulsant action* - Thiopentone is a potent **anticonvulsant** because it enhances the inhibitory effects of **GABA** in the central nervous system, which helps to suppress seizure activity. - It is used to terminate **status epilepticus** that is refractory to other treatments. *It can cause reflex tachycardia* - Thiopentone can cause **peripheral vasodilation** and a decrease in **blood pressure**, which may trigger a **reflex tachycardia** as the body attempts to compensate for the reduced systemic vascular resistance. - This effect is generally mild but can be more pronounced in hypovolemic patients or at higher doses.

Q: Which of the following is not a use of Thiopentone?

As antidepressant. As antidepressant - **Thiopentone** is a short-acting **barbiturate** and a potent central nervous system depressant, with no known antidepressant properties. [1] - Its mechanism of action involves enhancing **GABAergic inhibition**, leading to sedation and anesthesia, not mood elevation. *Induction of anesthesia* - **Thiopentone** is a classic intravenous anesthetic, often used for **rapid induction of general anesthesia** due to its fast onset of action. [2], [4] - It quickly crosses the **blood-brain barrier** to produce unconsciousness, making it effective for this purpose. [4] *Medically induced coma* - **Thiopentone** can be used to induce and maintain a **medically induced coma**, particularly in cases of severe head injury or status epilepticus, to reduce metabolic demand and cerebral edema. [3] - Its ability to significantly suppress brain activity makes it suitable for **neuroprotection** in critical care settings. [3] *As truth serum* - Historically, **thiopentone** (often referred to as **sodium pentothal**) has been colloquially known as a **"truth serum"** due to its ability to lower inhibitions and make subjects more loquacious. - While it can facilitate questioning by making individuals less guarded, its effectiveness as a reliable truth serum is largely unsubstantiated and ethically controversial.

Q: Which of the following antiepileptic drugs is associated with causing congenital heart disease in the fetus?

Valproate. ***Valproate*** - **Valproate** is associated with the **highest overall risk of major congenital malformations** among antiepileptic drugs, affecting **10-20%** of exposed fetuses - While **neural tube defects** (spina bifida) are the most characteristic malformation, **cardiac defects** (including atrial septal defects, ventricular septal defects, and coarctation of aorta) occur in approximately **2-3%** of exposed pregnancies - The teratogenic risk is **dose-dependent**, with higher doses (>1000 mg/day) carrying substantially greater risk - Valproate is classified as **FDA Category X** (contraindicated in pregnancy) due to its high teratogenic potential *Phenytoin* - **Phenytoin** is associated with **fetal hydantoin syndrome**, which includes craniofacial abnormalities, limb defects, nail hypoplasia, and growth restriction - Cardiac defects do occur with phenytoin exposure (particularly septal defects), with an estimated risk of **2-3%** - However, the **overall rate of major malformations** is lower than valproate (approximately 6-10%) - While cardiac defects are part of the phenytoin teratogenicity spectrum, valproate carries a higher absolute risk *Carbamazepine* - **Carbamazepine** is primarily associated with **neural tube defects** (0.5-1% risk), particularly spina bifida - The overall risk of major congenital malformations is **approximately 4-6%**, lower than both valproate and phenytoin - Cardiac defects can occur but are less frequently reported compared to other malformations *Barbiturates* - **Barbiturates** (such as phenobarbital) have teratogenic potential including cardiac defects and cleft palate - The overall risk of major malformations is **estimated at 5-7%** - While cardiac defects have been reported, the evidence base is less robust than for valproate, and the absolute risk is lower

Q: Withdrawal of which of the following substances is most commonly associated with piloerection?

Morphine. ***Morphine*** - **Piloerection**, or "goosebumps," is a classic symptom of **opioid withdrawal**, particularly from strong opioids like morphine, due to sympathetic nervous system overactivity. - This sympathetic hyperactivity also manifests as **dilated pupils**, rhinorrhea, lacrimation, and sweating during opioid withdrawal. *Cannabis* - Withdrawal symptoms from **cannabis** typically include irritability, anxiety, sleep disturbances, and decreased appetite, but not prominent piloerection. - The sympathetic activation seen with opioid withdrawal is generally absent in cannabis withdrawal. *Smoking* - **Nicotine withdrawal** is characterized by irritability, anxiety, difficulty concentrating, and increased appetite, but **piloerection** is not a common or prominent symptom. - Nicotine withdrawal primarily affects neuropsychological functions and cravings, rather than leading to significant sympathetic overdrive causing skin manifestations. *Alcohol* - **Alcohol withdrawal** can be severe, including tremors, hallucinations, and seizures (delirium tremens), but **piloerection** is not a hallmark symptom. - Alcohol withdrawal primarily involves central nervous system hyperexcitability and autonomic dysfunction, but "goosebumps" are not typically reported as a key feature.

Q: Local anaesthetic causing methemoglobinemia is ?

Benzocaine. ***Benzocaine*** - **Benzocaine** is a common cause of **methemoglobinemia**, particularly with topical application or excessive doses. - It converts **ferrous iron (Fe2+)** in hemoglobin to **ferric iron (Fe3+)**, leading to impaired oxygen binding and delivery. *Dibucaine* - **Dibucaine** is an amide-type local anesthetic with a long duration of action. - While it can cause systemic toxicity, it is **not commonly associated** with methemoglobinemia. *Chloroprocaine* - **Chloroprocaine** is an ester-type local anesthetic known for its rapid hydrolysis by plasma cholinesterases. - Its short half-life and rapid metabolism make **methemoglobinemia an unlikely side effect**. *Procaine* - **Procaine** is another ester-type local anesthetic, the first synthetic local anesthetic. - While all ester-type local anesthetics have a theoretical risk, **procaine is rarely implicated** in causing clinically significant methemoglobinemia compared to benzocaine.

Q: Which of the following serotonin receptors is classified as an ionotropic receptor?

5-HT3. ***5-HT3*** - The 5-HT3 receptor is unique among serotonin receptors as it is the **only ionotropic receptor**, meaning it directly gates an ion channel upon ligand binding. - Activation of 5-HT3 receptors leads to rapid **depolarization** of the neuronal membrane through the influx of **sodium and potassium ions**, mediating fast excitatory neurotransmission. *5-HT1A* - The 5-HT1A receptor is a **G-protein coupled receptor (GPCR)** and is inhibitory, primarily located pre- and post-synaptically in the brain. - Activation leads to a decrease in **cAMP** levels and opening of **potassium channels**, resulting in hyperpolarization. *5-HT1B* - The 5-HT1B receptor is also a **GPCR**, primarily found on presynaptic terminals where it acts as an **autoreceptor** to inhibit serotonin release. - Similar to 5-HT1A, its activation inhibits adenylyl cyclase activity, leading to reduced **cAMP** levels. *5-HT2A* - The 5-HT2A receptor is a **GPCR** that couples to the Gq protein, leading to increased **inositol triphosphate (IP3)** and **diacylglycerol (DAG)**. - This pathway activates protein kinase C and mobilizes intracellular calcium, typically leading to **excitatory effects** in various brain regions.

Q: Which drug is used to prolong the action of local anesthetics in hypertensive patients?

Felypressin. ***Felypressin*** - Felypressin is a **vasoconstrictor** that prolongs the action of local anesthetics by reducing their systemic absorption without causing significant **alpha-adrenergic stimulation**, making it a safer option for hypertensive patients. - It acts as a **vasopressin V1 receptor agonist**, leading to vasoconstriction primarily in the splanchnic and skeletal muscle beds, with less impact on cardiac function compared to adrenergic vasoconstrictors. *Clonidine* - Clonidine is an **alpha-2 adrenergic agonist** used as an adjuvant to local anesthetics, primarily for its **sedative** and **analgesic** properties, and to some extent for prolongation of block. - While it can prolong local anesthetic action, its primary use is not as a direct vasoconstrictor to reduce systemic absorption, and it can cause **hypotension** and **bradycardia**, which might complicate care in some hypertensive patients. *Dexmedetomidine* - Dexmedetomidine is a highly selective **alpha-2 adrenergic agonist** used for its **sedative** and **analgesic** effects, and as an adjunct to local anesthetics to prolong their duration. - Similar to clonidine, its primary role is not as a direct vasoconstrictor to minimize systemic absorption, and it carries the risk of **hypotension** and **bradycardia**, making it less ideal solely for vasoconstriction in hypertensive patients. *Noradrenaline* - Noradrenaline (norepinephrine) is a potent **alpha-1 adrenergic agonist** that causes intense vasoconstriction, which would significantly prolong the action of local anesthetics. - However, its strong vasoconstrictive effects and potential for **systemic arterial hypertension** and tachycardia make it generally contraindicated or used with extreme caution in hypertensive patients due to the risk of exacerbating their condition.

Q: Which drug is the first-line treatment for absence seizures?

Ethosuximide. ***Ethosuximide*** - **Ethosuximide** is the **first-line drug** of choice for treating **absence seizures** due to its specific mechanism of action in inhibiting **T-type calcium channels** in the thalamus. - Its efficacy is highly specific to **absence seizures**, meaning it is primarily effective for this type of seizure and generally not for other seizure types. *Lamotrigine* - While effective for various seizure types, including **generalized tonic-clonic seizures** and **focal seizures**, **lamotrigine** is considered a **second-line agent** for absence seizures. - It is often used when **ethosuximide** or **valproic acid** is not tolerated or ineffective, or when there are co-existing seizure types. *Carbamazepine* - **Carbamazepine** is a first-line treatment for **focal seizures** and **generalized tonic-clonic seizures**, but it is generally **contraindicated** for absence seizures. - In some cases, **carbamazepine** can paradoxically **worsen absence seizures** or precipitate them due to its distinct mechanism of action involving **sodium channel blockade**. *Phenytoin* - **Phenytoin** is primarily used for **focal seizures** and **generalized tonic-clonic seizures** by stabilizing neuronal membranes and reducing neuronal excitability via **sodium channel blockade**. - It is **not effective** for absence seizures and, like carbamazepine, can sometimes **exacerbate** them or has no beneficial effect.

Question 1

Which of the following is used for the patient on antiparkinsonian medication levodopa + carbidopa, but patient showing marked on-off effect?

Accepted Answer

Selegiline

Answer

Bromocriptine

Answer

Amantadine

Answer

Rimonabant

Question 2

Which of the following statements about the anti-Parkinson drug levodopa is true?

Accepted Answer

Only a small percentage of administered levodopa crosses the blood-brain barrier (approximately 2%).

Answer

Levodopa is an active metabolite of dopamine.

Answer

About 50% of administered levodopa is peripherally converted to dopamine.

Answer

Levodopa is not used in the management of hepatic coma.

Question 3

All of the following about thiopentone are true except which one?

Accepted Answer

IV injection is painless

Answer

It has anticonvulsant action

Answer

It can cause reflex tachycardia

Answer

It decreases ICP

Question 4

Which of the following is not a use of Thiopentone?

Accepted Answer

As antidepressant

Answer

Induction of anesthesia

Answer

Medically induced coma

Answer

As truth serum

Question 5

Which of the following antiepileptic drugs is associated with causing congenital heart disease in the fetus?

Accepted Answer

Valproate

Answer

Carbamazepine

Answer

Phenytoin

Answer

Barbiturates

Question 6

Withdrawal of which of the following substances is most commonly associated with piloerection?

Accepted Answer

Morphine

Answer

Cannabis

Answer

Smoking

Answer

Alcohol

Question 7

Local anaesthetic causing methemoglobinemia is ?

Accepted Answer

Benzocaine

Answer

Dibucaine

Answer

Chloroprocaine

Answer

Procaine

Question 8

Which of the following serotonin receptors is classified as an ionotropic receptor?

Accepted Answer

5-HT3

Answer

5-HT1A

Answer

5-HT1B

Answer

5-HT2A

Question 9

Which drug is used to prolong the action of local anesthetics in hypertensive patients?

Accepted Answer

Felypressin

Answer

Clonidine

Answer

Dexmedetomidine

Answer

Noradrenaline

Question 10

Which drug is the first-line treatment for absence seizures?

Accepted Answer

Ethosuximide

Answer

Carbamazepine

Answer

Phenytoin

Answer

Lamotrigine

Central Nervous System Pharmacology — MCQs

Central Nervous System Pharmacology — MCQs

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