Central Nervous System Pharmacology Practice Questions

Q: Which sedative agent facilitates GABAergic action but lacks anticonvulsant and muscle relaxant properties, and does not affect sleep?

Zolpidem. ### Explanation **Correct Answer: B. Zolpidem** **Mechanism and Rationale:** Zolpidem is a non-benzodiazepine sedative-hypnotic (Z-drug). While it facilitates GABAergic action like benzodiazepines, it is highly selective for the **$\alpha_1$ subunit** of the $GABA_A$ receptor [1]. * The **$\alpha_1$ subunit** mediates sedation and amnesia. * The **$\alpha_2, \alpha_3,$ and $\alpha_5$ subunits** are responsible for anxiolytic, muscle relaxant, and anticonvulsant effects. Because Zolpidem lacks significant affinity for these other subunits, it provides pure sedation without the muscle relaxant or anticonvulsant properties associated with traditional benzodiazepines [1]. Furthermore, it has minimal impact on sleep architecture (it does not significantly suppress REM or N3 sleep stages), making it ideal for treating insomnia [2]. **Analysis of Incorrect Options:** * **A. Diazepam:** A classic benzodiazepine that binds non-selectively to $\alpha_1, \alpha_2, \alpha_3,$ and $\alpha_5$ subunits. Consequently, it possesses potent anticonvulsant, muscle relaxant, and anxiolytic properties. * **C. Phenobarbitone:** A barbiturate that increases the *duration* of GABA channel opening. It is a powerful anticonvulsant and significantly alters sleep architecture (decreases REM sleep) [2]. * **D. Buspirone:** An anxiolytic that acts as a **5-$HT_{1A}$ partial agonist**. It does not facilitate GABAergic action and lacks sedative, anticonvulsant, or muscle relaxant properties. **High-Yield NEET-PG Pearls:** * **Z-drugs (Zolpidem, Zaleplon, Eszopiclone):** Preferred for insomnia due to low potential for tolerance, dependence, and "hangover" effects. * **Antidote:** Flumazenil reverses the effects of both Benzodiazepines and Z-drugs. * **Zaleplon:** Has the shortest half-life among Z-drugs, useful for sleep-onset insomnia. * **Eszopiclone:** Often used for long-term management of insomnia.

Q: A young man with a known history of heroin addiction is brought to the emergency department in an unconscious state. On examination, the patient presents with decreased bowel sounds, depressed respiration, and pinpoint pupils. What is the treatment of choice for this patient?

Intravenous naloxone. ### Explanation **Correct Answer: B. Intravenous naloxone** **Mechanism and Rationale:** The patient presents with the classic **"Opioid Overdose Triad"**: Coma (unconscious), Respiratory Depression, and Miosis (pinpoint pupils). Decreased bowel sounds further confirm opioid-induced slowing of gastrointestinal motility. In an acute emergency, the priority is to reverse respiratory depression. **Naloxone** is a competitive opioid antagonist with a high affinity for $\mu$-receptors. It is the treatment of choice because it acts rapidly (within 1–2 minutes when given IV) to displace the heroin from the receptors and restore spontaneous breathing. **Why other options are incorrect:** * **A. Oral naltrexone:** While naltrexone is an opioid antagonist, it has a long duration of action and is used for **relapse prevention** (maintenance therapy) in detoxified patients. It is not used in emergencies due to its slow onset and oral administration. * **C. Oral diazepam:** Diazepam is a benzodiazepine and a CNS depressant. Administering it to a patient with respiratory depression would worsen the condition and potentially be fatal. * **D. Oral buprenorphine:** This is a partial $\mu$-agonist used for opioid substitution therapy. In an acute overdose, adding a partial agonist will not provide the rapid reversal required and may even complicate the clinical picture. **High-Yield Clinical Pearls for NEET-PG:** * **Short Half-life:** Naloxone has a shorter half-life (approx. 30–60 mins) than most opioids (like heroin or methadone). Therefore, **repeated dosing** or an IV infusion may be necessary to prevent the patient from slipping back into a coma once the naloxone wears off. * **Diagnostic Use:** Naloxone is often used as a diagnostic tool in "coma of unknown origin." * **Withdrawal:** Rapid administration in an addict can precipitate **acute withdrawal syndrome** (agitation, vomiting, lacrimation, rhinorrhea).

Q: A patient on Phenytoin therapy develops depression, for which he was prescribed tricyclic antidepressants. He now complains of lassitude and his Hb reading is 8 gm/dl. What is the next step in the management of this patient?

Estimate MCV. ### Explanation **1. Why "Estimate MCV" is the correct answer:** The patient is presenting with symptoms of anemia (lassitude, Hb 8 gm/dl) while on long-term **Phenytoin** therapy. Phenytoin is a well-known inducer of **folate deficiency**, which leads to **Megaloblastic Anemia**. The mechanism involves Phenytoin interfering with intestinal folate absorption and increasing its metabolism. In megaloblastic anemia, the Mean Corpuscular Volume (MCV) is elevated (>100 fL). Therefore, estimating the MCV is the most appropriate next step to confirm the presence of macrocytosis before initiating folic acid supplementation. *Note:* Tricyclic antidepressants (TCAs) are mentioned as a distractor, though they can occasionally lower the seizure threshold, they are not the primary cause of the hematological findings here. **2. Why other options are incorrect:** * **Chest X-ray:** While Phenytoin can rarely cause interstitial lung disease, it does not explain the low hemoglobin and lassitude. * **Estimate GGT:** Gamma-glutamyl transferase (GGT) is a marker of enzyme induction or liver pathology. While Phenytoin is a potent hepatic enzyme inducer and can raise GGT levels, this test does not help diagnose the cause of the patient's anemia. **3. Clinical Pearls for NEET-PG:** * **Phenytoin Side Effects (Mnemonic: HOT MALAI):** **H**irsutism, **O**steomalacia, **T**eratogenicity (Fetal Hydantoin Syndrome), **M**egaloblastic anemia, **A**taxia, **L**ymphadenopathy, **A**rrythmias (on rapid IV), **I**nsulin inhibition (Hyperglycemia), and **Gingival Hyperplasia**. * **Folate Supplementation:** Giving folic acid to a patient on Phenytoin can actually *decrease* the serum levels of Phenytoin (by increasing its metabolism), potentially leading to breakthrough seizures. * **Zero-Order Kinetics:** Phenytoin follows saturation kinetics; small dose increases can lead to toxic levels.

Q: All of the following decrease skeletal muscle tone by CNS effects, except:

D-tubocurarin. Skeletal muscle relaxants are broadly classified into two categories based on their site of action: **Centrally acting muscle relaxants** and **Peripherally acting muscle relaxants**. ### **Explanation of the Correct Answer** **A. D-tubocurarine:** This is a **peripherally acting** neuromuscular blocker. It acts at the **Neuromuscular Junction (NMJ)** by competitively antagonizing nicotinic acetylcholine receptors ($N_m$) on the motor endplate. It does not cross the blood-brain barrier and, therefore, has **no CNS effects**. This makes it the "except" in the list. ### **Explanation of Incorrect Options** * **B. Diazepam:** A Benzodiazepine that acts centrally by enhancing **GABA-A** mediated presynaptic inhibition in the spinal cord. It is used for both muscle spasms and spasticity. * **C. Baclofen:** A centrally acting agent that is a selective **GABA-B agonist**. It acts primarily at the spinal level to reduce excitatory neurotransmitter release, effectively reducing spasticity in conditions like Multiple Sclerosis. * **D. Mephenesin:** The prototype of centrally acting muscle relaxants. It acts on the **internuncial neurons** of the spinal cord to reduce skeletal muscle tone without affecting consciousness. ### **High-Yield Clinical Pearls for NEET-PG** * **Dantrolene:** The only peripherally acting muscle relaxant that acts **directly on the muscle** (by inhibiting Calcium release from the Sarcoplasmic Reticulum via RyR1 receptors). It is the drug of choice for **Malignant Hyperthermia**. * **Tizanidine:** A centrally acting muscle relaxant that works as an **$\alpha_2$ adrenergic agonist** (similar to clonidine but with less hypotensive effect). * **Site Summary:** * CNS: Diazepam, Baclofen, Tizanidine. * NMJ: D-tubocurarine, Succinylcholine. * Muscle: Dantrolene.

Q: Which benzodiazepine does not have significant anticonvulsant properties?

Temazepam. **Explanation:** Benzodiazepines (BZDs) act by potentiating GABA-mediated inhibitory neurotransmission. While most BZDs share common properties (anxiolytic, sedative-hypnotic, muscle relaxant, and anticonvulsant), their clinical utility is determined by their specific receptor affinity and pharmacokinetic profile. **Why Temazepam is the correct answer:** Temazepam is a **short-to-intermediate acting BZD** primarily used as a **hypnotic** for the treatment of insomnia. It lacks significant anticonvulsant or muscle relaxant properties at standard therapeutic doses. Its pharmacological profile is optimized for inducing and maintaining sleep without the prolonged CNS depression required for seizure suppression. **Analysis of Incorrect Options:** * **Nitrazepam:** Primarily used as a hypnotic, but it possesses potent anticonvulsant properties and is clinically used in the management of infantile spasms (West Syndrome) and certain myoclonic seizures. * **Diazepam:** A prototype long-acting BZD. It is a first-line agent for terminating acute seizures and **Status Epilepticus** due to its high lipid solubility and rapid brain entry. * **Clonazepam:** A highly potent BZD specifically used as a long-term **antiepileptic drug**. It is the drug of choice for Absence seizures (as an alternative to Ethosuximide) and Myoclonic seizures. **NEET-PG High-Yield Pearls:** * **Status Epilepticus:** Lorazepam is often preferred over Diazepam due to its longer duration of action in the brain (less redistribution). * **Metabolism:** Temazepam, Oxazepam, and Lorazepam (**T-O-L**) undergo direct glucuronidation (Phase II) and do not form active metabolites, making them safer in elderly patients and those with liver failure. * **Antidote:** Flumazenil is the specific competitive antagonist for BZD overdose.

Q: Which of the following statements about vigabatrin is true?

Visual disturbances can occur. **Vigabatrin** is a structural analog of GABA that acts as an **irreversible inhibitor of GABA transaminase (GABA-T)**, the enzyme responsible for the degradation of GABA. By inhibiting this enzyme, it significantly increases the concentration of GABA (an inhibitory neurotransmitter) in the synaptic cleft. ### Why the correct answer is right: **Option D: Visual disturbances can occur.** The most significant and characteristic adverse effect of vigabatrin is **permanent bilateral concentric visual field constriction** (peripheral vision loss), occurring in up to 30-50% of patients. This is due to retinal toxicity. Because of this risk, it is usually reserved for refractory cases, and regular ophthalmological monitoring (perimetry) is mandatory. ### Why the other options are wrong: * **Option A:** Vigabatrin inhibits the *metabolism* of GABA, not its reuptake. **Tiagabine** is the drug that blocks neuronal and glial reuptake of GABA by inhibiting the GAT-1 transporter. * **Option B:** Vigabatrin is not used for absence seizures; in fact, it may **exacerbate** absence and myoclonic seizures. It is primarily used for refractory focal seizures and is the **drug of choice for Infantile Spasms (West Syndrome)** associated with Tuberous Sclerosis. * **Option C:** Life-threatening skin disorders (like Stevens-Johnson Syndrome) are more commonly associated with **Lamotrigine, Phenytoin, or Carbamazepine**, rather than Vigabatrin. ### High-Yield NEET-PG Pearls: * **Mechanism:** Irreversible "Suicide" inhibition of GABA-T. * **DOC:** Infantile Spasms (West Syndrome) in Tuberous Sclerosis. * **Black Box Warning:** Permanent vision loss (Vigabatrin Risk Evaluation and Mitigation Strategy - REMS program). * **Mnemonic:** **Vi**gabratrin **G**ABA **T**ransaminase inhibitor → **Vi**sual field defects.

Q: Which of the following drugs is an inverse agonist at H3 receptors used for the treatment of narcolepsy?

Pitolisant. Pitolisant is a first-in-class drug recently approved for the treatment of excessive daytime sleepiness (EDS) in adults with narcolepsy (with or without cataplexy). [1] 1. **Mechanism of Action:** Unlike H1 and H2 receptors which are postsynaptic, **H3 receptors** are primarily presynaptic autoreceptors located in the brain. [1] They normally inhibit the release of histamine. Pitolisant acts as a potent **selective H3-receptor antagonist/inverse agonist**. [1] By blocking these autoreceptors, it increases the synthesis and release of histamine in the brain, which promotes wakefulness and alertness (histamine is a major wake-promoting neurotransmitter). **Analysis of Incorrect Options:** * **A. Dexmedetomidine:** A highly selective **alpha-2 adrenergic agonist** used for sedation in intensive care settings and as an anesthetic adjunct. It causes sedation, not wakefulness. * **C. Icatibant:** A selective **bradykinin B2 receptor antagonist** used for the symptomatic treatment of acute attacks of hereditary angioedema (HAE). * **D. Secukinumab:** A human monoclonal antibody that binds to **Interleukin-17A (IL-17A)**, used in the treatment of psoriasis, ankylosing spondylitis, and psoriatic arthritis. **High-Yield Clinical Pearls for NEET-PG:** * **Narcolepsy Treatment Hierarchy:** Modafinil/Armodafinil (First-line), Pitolisant, Solriamfetol (DNRI), and Sodium Oxybate (for cataplexy). [2] * **Unique Feature:** Pitolisant is the only narcolepsy medication that is **not** classified as a controlled substance, as it lacks the typical abuse potential of stimulants. * **Metabolism:** It is metabolized by CYP2D6; dose adjustments are required in poor metabolizers or when given with drugs like paroxetine or fluoxetine.

Q: Which of the following tricyclic antidepressants is used for peripheral neuropathy?

amitriptyline. **Explanation:** **Amitriptyline** is the correct answer because it is the most widely used and clinically established Tricyclic Antidepressant (TCA) for the management of **neuropathic pain**, including diabetic peripheral neuropathy and post-herpetic neuralgia. Its mechanism involves the inhibition of serotonin and norepinephrine reuptake in the spinal cord, which enhances the descending inhibitory pathways of pain. Additionally, it blocks sodium channels and NMDA receptors, further contributing to its analgesic effect at doses lower than those required for depression. **Analysis of Incorrect Options:** * **B. Clomipramine:** While a potent TCA, it is primarily the drug of choice for **Obsessive-Compulsive Disorder (OCD)**. It is not typically used as a first-line agent for peripheral neuropathy. * **C. Fluoxetine:** This is an **SSRI** (Selective Serotonin Reuptake Inhibitor), not a TCA. SSRIs are generally considered ineffective for the treatment of neuropathic pain compared to TCAs or SNRIs (like Duloxetine). * **D. Imipramine:** Although imipramine is a TCA and has some analgesic properties, it is clinically preferred for **enuresis (bed-wetting)** in children and certain panic disorders. Amitriptyline remains the gold standard TCA for chronic pain. **High-Yield Clinical Pearls for NEET-PG:** * **First-line drugs for Neuropathic Pain:** Amitriptyline (TCA), Pregabalin/Gabapentin (Calcium channel ̡2-͂ ligands), and Duloxetine (SNRI). * **Side Effects of TCAs:** Due to anticholinergic activity, watch for "dry mouth, blurred vision, urinary retention, and constipation." They are contraindicated in patients with **glaucoma** and **prostatic hypertrophy**. * **ECG Changes:** TCAs can cause QRS prolongation; sodium bicarbonate is the antidote for TCA overdose.

Q: Dapoxetine is specifically developed for what condition?

Premature ejaculation. **Explanation:** **Dapoxetine** is a unique, short-acting **Selective Serotonin Reuptake Inhibitor (SSRI)** specifically designed and FDA-approved for the treatment of **Premature Ejaculation (PE)** in men aged 18–64 years. **1. Why Premature Ejaculation is Correct:** While most SSRIs are used for psychiatric disorders, they are known to cause "delayed ejaculation" as a side effect by increasing serotonin levels at the post-synaptic cleft, which inhibits the ejaculatory reflex. Dapoxetine was engineered to exploit this effect. Unlike fluoxetine or paroxetine, which have long half-lives, Dapoxetine is **rapidly absorbed and rapidly eliminated** (peak plasma concentration in 1 hour). This pharmacokinetic profile makes it ideal for **"on-demand"** dosing (taken 1–3 hours before intercourse) without causing the long-term systemic accumulation seen with antidepressants. **2. Why Other Options are Incorrect:** * **A & D (Depression and Anxiety):** Although Dapoxetine is an SSRI, its rapid clearance makes it ineffective for maintaining the steady-state neurotransmitter levels required to treat mood or anxiety disorders. * **B (Psychosis):** Psychosis is primarily managed with Dopamine (D2) receptor antagonists (Antipsychotics), not SSRIs. **High-Yield Clinical Pearls for NEET-PG:** * **Mechanism:** Inhibits serotonin transporter (SERT), increasing serotonin action at the pre-synaptic and post-synaptic receptors involved in the ejaculatory delay. * **Pharmacokinetics:** Shortest half-life among SSRIs (~1.5 hours). * **Contraindications:** Should not be used with potent CYP3A4 inhibitors or in patients with significant heart failure/permanent pacemaker dependency. * **Common Side Effects:** Nausea, dizziness, and headache.

Question 1

Which sedative agent facilitates GABAergic action but lacks anticonvulsant and muscle relaxant properties, and does not affect sleep?

Accepted Answer

Zolpidem

Answer

Diazepam

Answer

Phenobarbitone

Answer

Buspirone

Question 2

A young man with a known history of heroin addiction is brought to the emergency department in an unconscious state. On examination, the patient presents with decreased bowel sounds, depressed respiration, and pinpoint pupils. What is the treatment of choice for this patient?

Accepted Answer

Intravenous naloxone

Answer

Oral naltrexone

Answer

Oral diazepam

Answer

Oral buprenorphine

Question 3

A patient on Phenytoin therapy develops depression, for which he was prescribed tricyclic antidepressants. He now complains of lassitude and his Hb reading is 8 gm/dl. What is the next step in the management of this patient?

Accepted Answer

Estimate MCV

Answer

Chest X-ray

Answer

Estimate GGT

Answer

None of the above

Question 4

All of the following decrease skeletal muscle tone by CNS effects, except:

Accepted Answer

D-tubocurarin

Answer

Diazepam

Answer

Baclofen

Answer

Mephenesin

Question 5

All of the following are surface anesthetics except:

Accepted Answer

Bupivacaine

Answer

Lignocaine

Answer

Procaine

Answer

Cinchocaine

Question 6

Which benzodiazepine does not have significant anticonvulsant properties?

Accepted Answer

Temazepam

Answer

Nitrazepam

Answer

Diazepam

Answer

Clonazepam

Question 7

Which of the following statements about vigabatrin is true?

Accepted Answer

Visual disturbances can occur

Answer

Blocks neuronal reuptake of GABA

Answer

Drug of choice in absence seizures

Answer

Life-threatening skin disorders may occur

Question 8

Which of the following drugs is an inverse agonist at H3 receptors used for the treatment of narcolepsy?

Accepted Answer

Pitolisant

Answer

Dexmedetomidine

Answer

Icatibant

Answer

Secukinumab

Question 9

Which of the following tricyclic antidepressants is used for peripheral neuropathy?

Accepted Answer

amitriptyline

Answer

clomipramine

Answer

fluoxetine

Answer

imipramine

Question 10

Dapoxetine is specifically developed for what condition?

Accepted Answer

Premature ejaculation

Answer

Depression

Answer

Psychosis

Answer

Anxiety disorder

Central Nervous System Pharmacology — MCQs

Central Nervous System Pharmacology — MCQs

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