Central Nervous System Pharmacology Practice Questions

Q: What is the drug of choice for nocturnal enuresis?

Imipramine. **Explanation:** **Imipramine** is a Tricyclic Antidepressant (TCA) and is considered the drug of choice for the pharmacological management of **nocturnal enuresis** (bedwetting) in children above 6 years of age. Its efficacy is attributed to a triple mechanism of action: 1. **Anticholinergic effect:** It increases the bladder capacity by relaxing the detrusor muscle. 2. **Alpha-adrenergic stimulation:** It increases the tone of the internal urethral sphincter. 3. **Alteration of sleep architecture:** It lightens the depth of sleep, making the child more likely to wake up when the bladder is full. **Analysis of Incorrect Options:** * **Diazepam:** A benzodiazepine used for anxiety and seizures. It deepens sleep (Stage 4), which could potentially worsen enuresis. * **Amoxapine:** A tetracyclic antidepressant with dopamine-blocking properties. It is primarily used for major depression with psychotic features, not enuresis. * **Reboxetine:** A selective norepinephrine reuptake inhibitor (SNRI) used for depression; it lacks the significant anticholinergic profile required to treat enuresis effectively. **Clinical Pearls for NEET-PG:** * **First-line management:** Non-pharmacological therapy (bladder training and **enuresis alarms**) is always preferred before starting drugs. * **Alternative Drug:** **Desmopressin** (ADH analogue) is often preferred in modern practice due to a better safety profile, but in the context of classic pharmacology questions, Imipramine remains the standard answer. * **Caution:** Imipramine has a narrow therapeutic index; overdose can lead to life-threatening cardiac arrhythmias (QRS prolongation).

Q: Which of the following does not belong to the ester group of local anesthetics?

Dibucaine. Local anesthetics (LAs) are chemically classified into two categories based on the linkage between their aromatic and hydrophilic groups: **Esters** and **Amides**. ### 1. Why Dibucaine is the Correct Answer **Dibucaine** belongs to the **Amide group**. A simple high-yield rule for NEET-PG is the **"i" rule**: Amide local anesthetics have two "i"s in their name (e.g., L**i**doca**i**ne, Pr**i**loca**i**ne, Bup**i**vaca**i**ne, D**i**buca**i**ne), whereas Ester local anesthetics have only one "i" (e.g., Procaine, Benzocaine). Dibucaine is a potent, long-acting amide primarily used in spinal anesthesia and topical preparations. ### 2. Analysis of Incorrect Options * **A. Chloroprocaine:** An ester-linked LA. It is known for its rapid onset and short duration of action, often used in obstetrics because it is rapidly metabolized by plasma cholinesterase, minimizing fetal exposure. * **B. Tetracaine:** A potent, long-acting ester LA. It is frequently used for spinal and topical (ophthalmic) anesthesia. * **C. Benzocaine:** An ester LA. Due to its low solubility, it is used exclusively for topical anesthesia. It is a known cause of methemoglobinemia. ### 3. Clinical Pearls for NEET-PG * **Metabolism:** Esters are metabolized by **plasma pseudocholinesterase** (deficiency leads to prolonged action), while Amides are metabolized by **hepatic microsomal enzymes** (CYP450). * **Allergy:** Allergic reactions are more common with **Esters** due to the metabolite **Para-aminobenzoic acid (PABA)**. Amide allergies are extremely rare. * **Dibucaine Number:** This is a clinical test to identify individuals with atypical pseudocholinesterase. Dibucaine inhibits normal enzyme activity by 80%, but atypical enzyme by only 20%. A low Dibucaine number indicates a risk of prolonged apnea after succinylcholine administration.

Q: Which of the following is NOT a dopaminergic agonist used for the management of Parkinsonism?

Selegiline. ### Explanation The correct answer is **Selegiline** because it is a **Selective irreversible MAO-B inhibitor**, not a direct dopaminergic agonist. #### 1. Why Selegiline is the Correct Answer Selegiline works by inhibiting the enzyme **Monoamine Oxidase-B (MAO-B)**, which is responsible for the degradation of dopamine in the striatum. By blocking this enzyme, it increases the availability and prolongs the action of endogenous or exogenous dopamine. It does not directly stimulate dopamine receptors. #### 2. Analysis of Incorrect Options (Dopamine Agonists) These drugs act by directly stimulating dopamine receptors (primarily D2 and D3) in the brain: * **Bromocriptine (Option A):** An older, **Ergot-derived** dopamine agonist. Its use has declined due to side effects like retroperitoneal/pulmonary fibrosis and heart valve erythromelalgia. * **Ropinirole (Option B):** A **Non-ergot** dopamine agonist. It is highly selective for D2/D3 receptors and is frequently used in early Parkinsonism and Restless Leg Syndrome. * **Pramipexole (Option C):** Another **Non-ergot** agonist with antioxidant properties. Like Ropinirole, it is preferred over ergot derivatives due to a better safety profile. #### 3. NEET-PG High-Yield Pearls * **Cheese Reaction:** Selegiline is selective for MAO-B at low doses, so it **does not** typically cause the "cheese reaction" (hypertensive crisis) associated with non-selective MAO inhibitors. However, selectivity is lost at higher doses. * **Metabolism:** Selegiline is metabolized into **amphetamine and methamphetamine**, which can cause insomnia as a side effect. * **Neuroprotection:** Selegiline is hypothesized to have neuroprotective effects by reducing oxidative stress, though clinical evidence remains debated. * **Apomorphine:** Remember that Apomorphine is a potent injectable dopamine agonist used for "rescue" therapy during "off" episodes in advanced Parkinson’s.

Q: What is the drug of choice for status epilepticus?

Intravenous diazepam. **Explanation:** **Status Epilepticus (SE)** is a medical emergency defined as a seizure lasting >5 minutes or recurrent seizures without recovery of consciousness between episodes. The primary goal is rapid termination of seizure activity to prevent neuronal damage. **Why Intravenous (IV) Diazepam is correct:** Benzodiazepines are the first-line agents for SE due to their rapid onset of action. They act as positive allosteric modulators of **GABA-A receptors**, increasing chloride channel opening frequency and enhancing postsynaptic inhibition [1]. **IV Diazepam** is highly lipid-soluble, allowing it to cross the blood-brain barrier almost instantly, making it the drug of choice for immediate seizure cessation. **Why other options are incorrect:** * **Intramuscular (IM) Diazepam:** Absorption via the IM route is slow, erratic, and unpredictable. In an emergency like SE, the IV route is mandatory for immediate bioavailability. (Note: IM Midazolam is preferred if IV access cannot be established). * **Intramuscular (IM) Phenytoin:** Phenytoin is highly alkaline and causes significant tissue necrosis, pain, and "purple glove syndrome" when given IM. It also precipitates in the muscle, leading to poor absorption. * **Intravenous (IV) Phenytoin:** While used in SE, it is a **second-line** (maintenance) drug. It has a slower onset of action and must be infused slowly (max 50mg/min) to avoid cardiac arrhythmias and hypotension [1]. **NEET-PG High-Yield Pearls:** 1. **Drug of Choice (Initial):** IV Lorazepam (preferred over Diazepam in many guidelines due to longer duration of action in the brain) or IV Diazepam [1]. 2. **Best IM route drug:** IM Midazolam (if no IV access). 3. **Maintenance/Second-line:** IV Phenytoin or Fosphenytoin (Fosphenytoin is preferred as it can be infused faster and causes less local irritation). 4. **Refractory SE:** IV Phenobarbital, Thiopental, or Propofol.

Q: Which of the following drugs increases GABA levels in the brain?

Sodium valproate. **Explanation:** The question focuses on the mechanism of action of various antiepileptic and sedative-hypnotic drugs regarding their interaction with the GABAergic system. **Why Sodium Valproate is Correct:** Sodium Valproate is a broad-spectrum antiepileptic that increases the concentration of GABA (the primary inhibitory neurotransmitter) in the brain through a pleiotropic mechanism: 1. **Inhibition of GABA Transaminase (GABA-T):** It inhibits the enzyme responsible for the degradation of GABA. 2. **Stimulation of Glutamic Acid Decarboxylase (GAD):** It enhances the enzyme that synthesizes GABA from glutamate. 3. It also blocks voltage-gated sodium channels and T-type calcium channels. **Analysis of Incorrect Options:** * **Diazepam (Benzodiazepine):** It does not increase GABA levels. Instead, it acts as a **Positive Allosteric Modulator**. It increases the **frequency** of chloride channel opening in the presence of GABA. * **Phenobarbitone (Barbiturate):** It also does not increase GABA levels. It increases the **duration** of chloride channel opening and can act as a GABA-mimetic at high doses. * **Carbamazepine:** Its primary mechanism is the **blockade of use-dependent voltage-gated sodium channels**, preventing high-frequency repetitive firing of action potentials. It has no significant effect on GABA levels. **High-Yield Clinical Pearls for NEET-PG:** * **Vigabatrin** is another drug that increases GABA levels by **irreversibly** inhibiting GABA Transaminase (associated with visual field contraction). * **Tiagabine** increases GABA levels in the synaptic cleft by inhibiting the GABA transporter (**GAT-1**), preventing reuptake. * **Valproate** is the drug of choice for Generalized Tonic-Clonic Seizures (GTCS), Myoclonic seizures, and Absence seizures, but is highly **teratogenic** (causes Neural Tube Defects).

Q: The potential action of all the local anesthetics depends on the ability of anesthetic salt to liberate the free?

Alkaloidal base. **Explanation:** Local anesthetics (LAs) are chemically **weak bases**. For clinical use, they are formulated as water-soluble **hydrochloride salts** (e.g., Lidocaine HCl) to maintain stability in an acidic solution (pH 4–6). **Why "Alkaloidal Base" is correct:** To exert their effect, the anesthetic salt must dissociate in the body's tissues. According to the Henderson-Hasselbalch equation, when the salt is injected into the relatively more alkaline environment of the tissue (pH 7.4), it liberates the **unionized alkaloidal base**. This lipid-soluble free base is the only form capable of diffusing across the neuronal lipid bilayer. Once inside the axoplasm, the base re-equilibrates into an ionized (cationic) form, which binds to the internal subunit of the voltage-gated sodium channel to block nerve conduction. **Analysis of Incorrect Options:** * **Acid medium:** An acidic environment (like an abscess or inflamed tissue) increases the ionized fraction of the drug. This prevents the liberation of the free base, leading to poor penetration and clinical failure of the anesthesia. * **Neutral medium:** While closer to physiological pH than the storage vial, the term "neutral medium" does not describe the chemical entity (the base) required for membrane diffusion. * **Alkaloidal chelate:** This is a distracter term; local anesthetics do not function via chelation. **High-Yield Clinical Pearls for NEET-PG:** * **Mechanism:** LAs block **Voltage-gated Na+ channels** from the *inside*. * **Inflammation:** "LAs do not work in pus" because the low pH ionizes the drug, preventing it from crossing the cell membrane. * **Bicarbonate:** Adding Sodium Bicarbonate to LAs (alkalinization) speeds up the onset of action by increasing the concentration of the free alkaloidal base. * **Order of Blockade:** Small myelinated fibers > Unmyelinated fibers. (Autonomic > Pain > Touch > Temperature > Proprioception > Motor).

Q: Which of the following is true about local anesthetic agents?

All of the above.. This question tests the fundamental pharmacological properties of local anesthetics (LAs), which are high-yield topics for NEET-PG. ### **Mechanism and Pharmacokinetics** The clinical profile of a local anesthetic is determined by its chemical structure and physicochemical properties: 1. **Potency and Lipid Solubility (Option B):** The nerve cell membrane is composed of a lipid bilayer. Therefore, the more lipid-soluble a drug is, the more easily it can penetrate the neuronal membrane to reach its site of action (the voltage-gated sodium channel). **Higher lipid solubility = Higher potency.** (e.g., Bupivacaine is more lipid-soluble and potent than Lidocaine). 2. **Duration of Action and Protein Binding (Option A):** Local anesthetics bind primarily to **alpha-1 acid glycoprotein**. Drugs that bind more firmly to these proteins remain at the receptor site for a longer period, resisting systemic absorption. **Higher protein binding = Longer duration of action.** (e.g., Bupivacaine has 95% protein binding and a long duration). 3. **Active Form and Protein Binding (Option C):** Only the **free (unbound) fraction** of a drug is pharmacologically active and capable of diffusing across membranes. Therefore, agents with lower protein binding have a higher concentration of free drug available to initiate an effect. ### **NEET-PG High-Yield Pearls** * **Onset of Action:** Depends on the **pKa**. The closer the pKa is to the physiological pH (7.4), the higher the concentration of the non-ionized form, leading to a faster onset. (Exception: Benzocaine). * **Differential Block:** Autonomic fibers (B) and Pain/Temperature fibers (A-delta/C) are blocked before motor fibers (A-alpha). * **Metabolism:** **Esters** (one 'i' in the name, e.g., Procaine) are metabolized by plasma pseudocholinesterase; **Amides** (two 'i's in the name, e.g., Lignocaine) are metabolized by liver microsomal enzymes.

Q: Which dopamine receptor exhibits an inhibitory action?

D2. **Explanation:** Dopamine receptors belong to the **G-protein coupled receptor (GPCR)** superfamily and are categorized into two main functional families based on their effect on the enzyme adenylyl cyclase. 1. **D2-like Family (D2, D3, D4):** These receptors are coupled to **Gi/o proteins**. Their activation **inhibits** the enzyme adenylyl cyclase, leading to a decrease in intracellular cyclic AMP (cAMP) levels. They also open potassium channels and close voltage-gated calcium channels, resulting in an overall inhibitory effect on the post-synaptic neuron. 2. **D1-like Family (D1, D5):** These receptors are coupled to **Gs proteins**. Their activation **stimulates** adenylyl cyclase, increasing cAMP levels and exerting an excitatory effect. **Analysis of Options:** * **Option C (D2):** Correct. As part of the D2-like family, it mediates inhibitory neurotransmission. It is the primary target for most antipsychotic drugs. * **Options A & B (D5 & D1):** Incorrect. Both belong to the D1-like family and are excitatory in nature (stimulate cAMP). * **Option D:** Incorrect, as D2 is a well-established inhibitory receptor. **High-Yield Clinical Pearls for NEET-PG:** * **Antipsychotics:** Most typical antipsychotics (e.g., Haloperidol) act by blocking **D2 receptors** in the mesolimbic pathway. * **Parkinson’s Disease:** Results from a loss of dopaminergic neurons in the substantia nigra. Treatment involves D2 agonists (e.g., Bromocriptine, Pramipexole). * **Location:** D1 and D2 are the most abundant dopamine receptors in the striatum. D4 receptors are specifically targeted by the atypical antipsychotic **Clozapine**.

Q: Which of the following drugs are used in Generalized Tonic-Clonic Seizures (GTCS)?

Ethosuximide. **Explanation** The correct answer is **Ethosuximide**. **1. Why Ethosuximide is the Correct Answer:** Ethosuximide is the drug of choice for **Absence Seizures** (Petit Mal). Its mechanism of action involves the inhibition of **T-type Calcium channels** in thalamic neurons. While it is highly effective for absence seizures, it is notably **ineffective** against Generalized Tonic-Clonic Seizures (GTCS). In fact, if a patient has a combination of absence seizures and GTCS, ethosuximide alone may precipitate or worsen GTCS. **2. Analysis of Incorrect Options:** * **Sodium Valproate:** This is a broad-spectrum antiepileptic and is considered the **drug of choice for GTCS**, as well as myoclonic and atonic seizures. * **Lamotrigine:** Another broad-spectrum agent effective against GTCS. It acts by blocking voltage-gated sodium channels and inhibiting glutamate release. * **Propofol:** While used in the management of refractory **Status Epilepticus** (to induce anesthesia), it is not a standard maintenance therapy for GTCS. **3. High-Yield Clinical Pearls for NEET-PG:** * **Drug of Choice for GTCS:** Sodium Valproate (First line); Levetiracetam or Lamotrigine (Alternatives). * **Drug of Choice for Absence Seizures:** Ethosuximide (if only absence); Sodium Valproate (if absence + GTCS). * **Narrow-spectrum drugs to avoid in GTCS/Myoclonic seizures:** Carbamazepine, Phenytoin, and Vigabatrin (these can paradoxically worsen generalized seizures). * **Teratogenicity:** Valproate is associated with Neural Tube Defects (highest risk), while Lamotrigine is considered one of the safest in pregnancy.

Question 1

What is the drug of choice for nocturnal enuresis?

Accepted Answer

Imipramine

Answer

Diazepam

Answer

Amoxapine

Answer

Reboxetine

Question 2

Which of the following does not belong to the ester group of local anesthetics?

Accepted Answer

Dibucaine

Answer

Chloroprocaine

Answer

Tetracaine

Answer

Benzocaine

Question 3

Which of the following is NOT a dopaminergic agonist used for the management of Parkinsonism?

Accepted Answer

Selegiline

Answer

Bromocriptine

Answer

Ropinirole

Answer

Pramipexole

Question 4

Which one of the following statements regarding drug effects on serotonin receptor systems is accurate?

Accepted Answer

5HT2 receptor blockers counteract bronchoconstriction and diarrhea of carcinoid.

Answer

Sumatriptan is an antiemetic because it blocks 5HT3 receptors.

Answer

MAO type B inhibitors lead to increased levels of serotonin in the CNS.

Answer

Ondansetron is used in migraine because it activates 5HT1D receptors.

Question 5

What is the drug of choice for status epilepticus?

Accepted Answer

Intravenous diazepam

Answer

Intramuscular diazepam

Answer

Intramuscular phenytoin

Answer

Intravenous phenytoin

Question 6

Which of the following drugs increases GABA levels in the brain?

Accepted Answer

Sodium valproate

Answer

Diazepam

Answer

Phenobarbitone

Answer

Carbamazepine

Question 7

The potential action of all the local anesthetics depends on the ability of anesthetic salt to liberate the free?

Accepted Answer

Alkaloidal base

Answer

Acid medium

Answer

Neutral medium

Answer

Alkaloidal chelate

Question 8

Which of the following is true about local anesthetic agents?

Accepted Answer

All of the above.

Answer

Duration of action depends on protein binding.

Answer

Potency depends upon lipid solubility.

Answer

Local anesthetics with low protein binding are more active.

Question 9

Which dopamine receptor exhibits an inhibitory action?

Accepted Answer

D2

Answer

D5

Answer

Di

Answer

None

Question 10

Which of the following drugs are used in Generalized Tonic-Clonic Seizures (GTCS)?

Accepted Answer

Ethosuximide

Answer

Sodium valproate

Answer

Lamotrigine

Answer

Propofol

Central Nervous System Pharmacology — MCQs

Central Nervous System Pharmacology — MCQs

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