Central Nervous System Pharmacology Practice Questions

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 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.

Q: Patient on treatment with carbidopa + levodopa for 10 years now has wearing-off effect. What should be added to restore action?

Tolcapone. ***Tolcapone*** - **Tolcapone** is a **catechol-O-methyltransferase (COMT) inhibitor** that prevents the peripheral breakdown of levodopa, increasing its availability to the brain. - Adding a COMT inhibitor is the **primary strategy** to mitigate the **wearing-off effect** in patients receiving chronic levodopa therapy by prolonging levodopa's half-life and duration of action. - COMT inhibitors directly extend the duration of each levodopa dose, making them first-line adjuncts for wearing-off phenomenon. *Rasagiline* - **Rasagiline** is a **monoamine oxidase-B (MAO-B) inhibitor** used in Parkinson's disease to reduce the breakdown of dopamine in the brain. - It is also effective as an adjunct in treating **wearing-off** and can reduce daily off-time, though COMT inhibitors are typically preferred as first-line agents for this specific indication. - MAO-B inhibitors work by increasing central dopamine levels rather than directly extending levodopa's duration. *Benzhexol* - **Benzhexol** (also known as trihexyphenidyl) is an **anticholinergic agent** primarily used to treat tremor and dystonia in Parkinson's disease, especially in younger patients. - It does not address the aetiology of the **wearing-off phenomenon**, which is due to fluctuating levodopa levels and dopamine deficiency. *Amantadine* - **Amantadine** is an **NMDA receptor antagonist** used primarily to reduce **dyskinesias** associated with long-term levodopa therapy in Parkinson's disease. - While it has some efficacy in early Parkinson's and improving motor fluctuations, it is not the primary intervention for the **wearing-off effect** where reduced duration of benefit from levodopa is the main issue.

Q: Which of the following drugs does not potentiate the effect of NMDA at NMDA receptors?

Ketamine. ***Ketamine*** - **Ketamine** is an **NMDA receptor antagonist**, meaning it blocks the activity of NMDA receptors rather than potentiating it. - It binds to a site within the **NMDA receptor channel**, preventing ion flow and neuronal excitation. - Used clinically as a dissociative anesthetic and for treatment-resistant depression. *Aspartic acid* - **Aspartic acid** functions as an **excitatory neurotransmitter** and is an **agonist** at NMDA receptors. - It readily activates these receptors by binding to the glutamate-binding site, thereby potentiating their effects. *D-serine* - **D-serine** acts as an **endogenous co-agonist** at the NMDA receptor by binding to the **glycine regulatory site** (also called the glycine-B site). - Its binding is essential for the full activation and potentiation of NMDA receptor activity. - Along with glycine, it is one of the primary physiological co-agonists required for NMDA receptor function. *Homocysteic acid* - **Homocysteic acid** is an **endogenous excitatory amino acid** that acts as an **agonist** at NMDA receptors. - It directly binds to and activates NMDA receptors at the glutamate-binding site, thus potentiating their effects.

Q: Which drug is used in amytrophic lateral sclerosis?

Riluzole. ***Riluzole*** - **Riluzole** is an **NMDA receptor antagonist** that is approved for the treatment of **amyotrophic lateral sclerosis (ALS)**. - It works by reducing **glutamate-mediated excitotoxicity**, which is thought to contribute to neuronal damage in ALS, thereby extending survival time and delaying the need for tracheostomy. *Glatiramer acetate* - **Glatiramer acetate** is an immunomodulating drug used in the treatment of **multiple sclerosis (MS)**. - It is believed to work by inducing and activating **T-suppressor cells** specific for myelin basic protein, thus reducing the frequency of relapses in MS. *Tacrine* - **Tacrine** is an **acetylcholinesterase inhibitor** that was previously used for the treatment of **mild to moderate Alzheimer's disease**. - Its use has largely been replaced by newer, better-tolerated drugs due to its significant **hepatotoxicity** and frequent dosing schedule. *Olanzapine* - **Olanzapine** is an **atypical antipsychotic** medication used to treat conditions such as **schizophrenia** and **bipolar disorder**. - It primarily exerts its effects by blocking **dopamine D2** and **serotonin 5-HT2A** receptors.

Q: Which of the following statements about oxcarbazepine is incorrect?

Less chances of hyponatremia than carbamazepine. ***Correct Answer: Less chances of hyponatremia than carbamazepine*** - This statement is **incorrect** because oxcarbazepine has a **higher incidence of hyponatremia** (up to 25% of patients) compared to carbamazepine (5-10%). - Hyponatremia is a well-known and dose-related adverse effect of oxcarbazepine, often requiring monitoring of serum sodium levels. - This is the most definitively incorrect statement among the options. *Incorrect: Metabolises itself* - While this statement is somewhat ambiguous, it likely refers to **autoinduction of metabolism**, which is a characteristic of **carbamazepine** [1]. - **Oxcarbazepine** is a prodrug that is rapidly converted to its active metabolite monohydroxy derivative (MHD), but it **does not autoinduce its own metabolism** to a significant extent like carbamazepine does [1]. - However, if interpreted literally, oxcarbazepine does undergo metabolism, making this statement potentially confusing. *Incorrect: Less chances of hepatotoxicity than carbamazepine* - This statement is **correct** about oxcarbazepine. It is generally associated with a **lower risk of severe hepatotoxicity** [1] compared to carbamazepine. - While liver enzyme elevations can occur, serious liver damage is much less common with oxcarbazepine. *Incorrect: It is less enzyme inducer than carbamazepine* - This statement is **correct** about oxcarbazepine. Its active metabolite MHD is a **weaker inducer of cytochrome P450 enzymes** (especially CYP3A4) than carbamazepine. - This translates to fewer and less significant drug-drug interactions with oxcarbazepine.

Q: What is the classification of Rotigotine?

Dopamine agonist. ***Dopamine agonist*** - Rotigotine is classified as a **non-ergoline dopamine agonist**, meaning it directly stimulates dopamine receptors in the brain. - It is used in the treatment of **Parkinson's disease** and **restless legs syndrome** by mimicking the effects of dopamine. *Dopamine antagonist* - **Dopamine antagonists** block dopamine receptors and are typically used as antipsychotics or antiemetics. - This classification would have opposite pharmacological effects to what is seen with rotigotine. *GABA agonist* - **GABA agonists** enhance the effects of the inhibitory neurotransmitter GABA, leading to sedation or seizure control. - This mechanism of action is unrelated to rotigotine's primary effects on dopamine pathways. *GABA antagonist* - **GABA antagonists** block GABA receptors, which can lead to increased neuronal excitability and seizures. - This is not the mechanism of action for rotigotine, which targets the dopaminergic system.

Q: What is the drug of choice for treating restless leg syndrome in a woman who developed pain and crawling sensation on her legs at night?

Pramipexole. ***Pramipexole*** - **Pramipexole** is a **dopamine agonist** (D2/D3 receptor agonist) that is highly effective in treating **restless leg syndrome (RLS)** and is FDA-approved for moderate-to-severe RLS. - It helps alleviate the characteristic **pain, crawling sensations (paresthesias)**, and the urge to move the legs, especially at night. - **First-line treatment** along with other dopamine agonists like ropinirole and rotigotine. - **Preferred in many guidelines** as a primary pharmacological option for RLS. *Gabapentin* - **Gabapentin** (and gabapentin enacarbil) is an **alpha-2-delta ligand** that is also considered a **first-line treatment option** for RLS per recent guidelines. - Particularly useful in patients with **comorbid insomnia, neuropathic pain**, or when there is concern about **augmentation** (worsening of symptoms with long-term dopamine agonist use). - While equally effective, **dopamine agonists like pramipexole** are more traditionally recognized as the primary choice in conventional teaching and previous exam questions. *Vitamin B12* - **Vitamin B12 deficiency** can cause **neurological symptoms** like numbness or tingling, but supplementation is **not a direct treatment for primary RLS** unless a specific deficiency is identified and contributing to symptoms. - No direct evidence supporting **Vitamin B12 supplementation** as a primary treatment for RLS itself. *Iron tablets* - **Iron deficiency** (ferritin <75 μg/L) is a common and important cause of **secondary RLS**, and **iron supplementation** should be considered when low iron stores are identified. - However, for primary RLS or without confirmed iron deficiency, iron tablets are **not the primary pharmacological treatment**, and dopamine agonists like pramipexole remain the preferred initial option.

Q: Modafinil is primarily used for the treatment of which of the following conditions?

Narcolepsy. ***Narcolepsy*** - **Modafinil** is a **eugeroic** (wakefulness-promoting agent) specifically approved and widely used for the treatment of excessive daytime sleepiness associated with **narcolepsy**. - Its mechanism involves increasing **dopamine** and **norepinephrine** levels, and modulating **orexin** pathways, promoting alertness without significant psychomotor stimulation. *Sexual dysfunction* - While sometimes explored off-label for certain types of sexual dysfunction, **modafinil** is not a primary or approved treatment for this condition. - Primary treatments for sexual dysfunction often involve specific medications like **PDE5 inhibitors** or hormone therapy, depending on the cause. *Depression* - **Modafinil** is not a primary antidepressant, although it can be used as an **adjunctive therapy** in some cases to combat residual fatigue or hypersomnia associated with depression. - Standard treatment for depression involves **selective serotonin reuptake inhibitors (SSRIs)**, **serotonin-norepinephrine reuptake inhibitors (SNRIs)**, or other classes of antidepressants. *Anxiety* - **Modafinil** is a stimulant-like drug and can sometimes **exacerbate anxiety** in susceptible individuals due to its catecholaminergic effects. - Primary treatments for anxiety disorders include **selective serotonin reuptake inhibitors (SSRIs)**, **benzodiazepines** (for acute relief), and psychotherapy.

Question 1

Local anaesthetic causing methemoglobinemia is ?

Accepted Answer

Benzocaine

Answer

Dibucaine

Answer

Chloroprocaine

Answer

Procaine

Question 2

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

Accepted Answer

Felypressin

Answer

Clonidine

Answer

Dexmedetomidine

Answer

Noradrenaline

Question 3

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

Accepted Answer

Ethosuximide

Answer

Carbamazepine

Answer

Phenytoin

Answer

Lamotrigine

Question 4

Patient on treatment with carbidopa + levodopa for 10 years now has wearing-off effect. What should be added to restore action?

Accepted Answer

Tolcapone

Answer

Benzhexol

Answer

Rasagiline

Answer

Amantadine

Question 5

Which of the following drugs does not potentiate the effect of NMDA at NMDA receptors?

Accepted Answer

Ketamine

Answer

Aspartic acid

Answer

D-serine

Answer

Homocysteic acid

Question 6

Which drug is used in amytrophic lateral sclerosis?

Accepted Answer

Riluzole

Answer

Tacrine

Answer

Olanzapine

Answer

Glatiramer acetate

Question 7

Which of the following statements about oxcarbazepine is incorrect?

Accepted Answer

Less chances of hyponatremia than carbamazepine

Answer

Metabolises itself

Answer

Less chances of hepatotoxicity than carbamazepine

Answer

It is less enzyme inducer than carbamazepine

Question 8

What is the classification of Rotigotine?

Accepted Answer

Dopamine agonist

Answer

Dopamine antagonist

Answer

GABA agonist

Answer

GABA antagonist

Question 9

What is the drug of choice for treating restless leg syndrome in a woman who developed pain and crawling sensation on her legs at night?

Accepted Answer

Pramipexole

Answer

Gabapentin

Answer

Vitamin B12

Answer

Iron tablets

Question 10

Modafinil is primarily used for the treatment of which of the following conditions?

Accepted Answer

Narcolepsy

Answer

Sexual dysfunction

Answer

Depression

Answer

Anxiety

Central Nervous System Pharmacology — MCQs

Central Nervous System Pharmacology — MCQs

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