General Pharmacology Practice Questions

Q: Which of the following receptors has an intrinsic ion channel?

GABA A receptor. The question tests the classification of receptors based on their signaling mechanisms. Receptors are broadly categorized into four types: Ionotropic, Metabotropic (G-protein coupled), Enzyme-linked, and Nuclear receptors [3]. The most commonly observed post-receptor events for some receptors involve changes in ion flux through channels formed by multi-subunit receptor complexes [4]. **1. Why GABA A is correct:** The **GABA A receptor** is a classic example of a **Ligand-gated ion channel (Ionotropic receptor)**. It is a pentameric structure that, upon binding with GABA, opens an **intrinsic chloride (Cl⁻) channel** [2, 3]. The influx of chloride ions leads to hyperpolarization of the post-synaptic neuron, resulting in rapid inhibitory neurotransmission. **2. Why the other options are incorrect:** * **Insulin receptor:** This is an **Enzyme-linked receptor** (specifically, a Receptor Tyrosine Kinase). It does not have an ion channel; instead, it triggers an intracellular phosphorylation cascade. * **Vitamin A receptor (RAR/RXR):** This is a **Nuclear receptor**. It acts as a transcription factor in the nucleus to regulate gene expression. * **GABA B receptor:** Unlike GABA A, GABA B is a **G-protein coupled receptor (GPCR)** [1]. It works indirectly by inhibiting adenylyl cyclase or opening potassium channels via G-proteins, rather than having an intrinsic channel [1]. **Clinical Pearls for NEET-PG:** * **Fastest receptors:** Ionotropic (milliseconds); **Slowest receptors:** Nuclear (hours to days). * **GABA A Modulators:** Benzodiazepines (increase frequency of channel opening) and Barbiturates (increase duration of channel opening). * **Other Ionotropic Receptors:** Nicotinic ACh receptors (NM and NN), NMDA, AMPA, and 5-HT3 receptors. All other 5-HT receptors are GPCRs [5].

Q: Which of the following is an enzyme inhibitor?

Disulfiram. **Explanation:** The correct answer is **Disulfiram (Option B)**. **1. Why Disulfiram is the correct answer:** Disulfiram is a classic example of a **specific enzyme inhibitor**. It works by irreversibly inhibiting the enzyme **Aldehyde Dehydrogenase (ALDH)**. In the metabolism of ethanol, alcohol is converted to acetaldehyde, which ALDH then converts to acetic acid. By inhibiting this enzyme, disulfiram causes a toxic accumulation of acetaldehyde in the blood, leading to the "Disulfiram-like reaction" (flushing, tachycardia, nausea, and palpitations). This is used clinically as aversion therapy for chronic alcoholism. **2. Analysis of Incorrect Options:** * **Phenobarbitone (Option A):** This is a potent **Microsomal Enzyme Inducer**. It increases the synthesis of Cytochrome P450 enzymes (specifically CYP2B6), leading to faster metabolism of co-administered drugs like warfarin. * **Phenytoin (Option C):** Another well-known **Enzyme Inducer**. Like phenobarbitone, it induces hepatic enzymes, which can lead to therapeutic failure of other drugs (e.g., oral contraceptives). * **Carbon tetrachloride (Option D):** This is a **hepatotoxin**, not a therapeutic enzyme inhibitor. It causes centrilobular necrosis through lipid peroxidation via its metabolite, the free radical $CCl_3$. **3. High-Yield NEET-PG Pearls:** * **Mnemonic for Enzyme Inducers (GPRS Cell Phone):** **G**riseofulvin, **P**henytoin, **R**ifampicin, **S**moking, **C**arbamazepine, **P**henobarbitone. * **Mnemonic for Enzyme Inhibitors (VITAMIN K):** **V**alproate, **I**soniazid, **T**rimethoprim, **A**miodarone, **M**acrolides (except Azithromycin), **I**ndinavir, **N**ilotinib, **K**etoconazole (and Cimetidine/Grapefruit juice). * **Suicide Inhibition:** Disulfiram is often categorized as a suicide inhibitor because the enzyme is permanently inactivated until new protein is synthesized.

Q: All the following drugs cross the blood-brain barrier EXCEPT one?

Dopamine. ### Explanation The ability of a drug to cross the **Blood-Brain Barrier (BBB)** depends on its lipid solubility, molecular size, and ionization state. The BBB is a highly selective semipermeable border of endothelial cells with tight junctions that prevents the passage of large or highly polar (hydrophilic) molecules. **Why Dopamine is the Correct Answer:** **Dopamine** is a highly polar, ionized catecholamine. Due to its hydrophilic nature, it cannot cross the BBB. In clinical practice, this is why dopamine cannot be used to treat Parkinson’s disease. Instead, its precursor **Levodopa (L-Dopa)** is used because it can cross the BBB via a neutral amino acid transporter, where it is then decarboxylated into dopamine within the CNS. **Analysis of Incorrect Options:** * **Morphine:** While less lipid-soluble than heroin, morphine is still lipophilic enough to cross the BBB and exert its analgesic effects on opioid receptors in the brain. * **Propranolol:** This is a highly lipid-soluble, non-selective beta-blocker. Its high CNS penetration explains its effectiveness in treating essential tremors and its potential side effects like vivid dreams or depression. * **Ether:** As a volatile general anesthetic, ether is highly lipid-soluble. All general anesthetics must cross the BBB rapidly to induce anesthesia. **NEET-PG High-Yield Pearls:** 1. **Physiological "Gaps":** The BBB is absent in the **Circumventricular Organs** (e.g., Area Postrema/CTZ, Posterior Pituitary). This allows the CTZ to detect toxins in the blood and induce vomiting. 2. **Inflammation:** Meningitis increases the permeability of the BBB, allowing drugs like **Penicillin G** (which normally has poor CNS penetration) to reach therapeutic levels in the CSF. 3. **Antihistamines:** 1st-generation antihistamines (e.g., Diphenhydramine) cross the BBB causing sedation, whereas 2nd-generation (e.g., Loratadine) do not.

Q: Which drug can directly release histamine from mast cells without involving an antigen-antibody reaction?

All of the above. The correct answer is **D. All of the above**. This question tests the concept of **Non-immunologic (Direct) Histamine Release**. Unlike Type I hypersensitivity reactions, which require prior sensitization and IgE-mediated cross-linking on mast cells [2], certain drugs can trigger mast cell degranulation directly by activating G-proteins or specific receptors (like MRGPRX2) on the cell surface. * **d-tubocurarine:** This skeletal muscle relaxant is a classic example of a drug that causes direct histamine release [1], often leading to bronchospasm and hypotension during anesthesia. * **Morphine:** Opioids, particularly morphine and codeine, are well-known for direct mast cell degranulation [1]. This often manifests clinically as "morphine itch" (pruritus) or urticaria at the injection site. * **Vancomycin:** Rapid intravenous infusion of vancomycin can cause widespread histamine release, leading to the **"Red Man Syndrome"** (erythema of the face, neck, and upper torso). This is a rate-dependent infusion reaction, not a true allergy. **Clinical Pearls for NEET-PG:** 1. **Red Man Syndrome Prevention:** Vancomycin should be infused slowly (over at least 60 minutes) to minimize direct histamine release. 2. **Other Drugs:** Other agents causing direct release include **Amphotericin B, Radiocontrast media, and Polymyxin B**. 3. **Treatment:** Since these are not IgE-mediated, they do not require prior exposure. Management involves slowing the infusion rate and administering H1-receptor antagonists (antihistamines). 4. **Succinylcholine vs. Atracurium:** Among muscle relaxants, **Atracurium** and **Mivacurium** are also significant histamine releasers, whereas Vecuronium and Rocuronium have minimal effects.

Q: What is the drug of choice for mountain sickness?

Acetazolamide. **Explanation:** **Acetazolamide** is the drug of choice for the prevention and treatment of **Acute Mountain Sickness (AMS)**. **Mechanism of Action:** At high altitudes, low oxygen levels (hypoxia) trigger hyperventilation, which leads to excessive loss of $CO_2$ and results in **respiratory alkalosis**. This alkalosis inhibits the respiratory center, preventing further compensatory breathing. Acetazolamide, a **Carbonic Anhydrase Inhibitor**, works by: 1. Inhibiting the enzyme in the proximal convoluted tubule, leading to **bicarbonate diuresis**. 2. This induces a mild **metabolic acidosis**, which counteracts the respiratory alkalosis. 3. The resulting decrease in blood pH stimulates the chemoreceptors, increasing the respiratory drive and improving oxygenation (speeding up acclimatization). **Analysis of Incorrect Options:** * **Cinnarizine:** An H1-antihistamine and calcium channel blocker used primarily for **motion sickness** and vertigo, not altitude sickness. * **Furosemide:** A loop diuretic used to treat High-Altitude Pulmonary Edema (HAPE) by reducing fluid in the lungs, but it is not the drug of choice for standard mountain sickness. * **Betahistine:** An H3-antagonist/H1-agonist used for **Meniere’s disease** to reduce vertigo; it has no role in altitude-related hypoxia. **High-Yield Clinical Pearls for NEET-PG:** * **Prophylaxis:** Acetazolamide should be started 24 hours before ascent. * **Side Effect:** A common side effect is **paresthesia** (tingling in fingers/toes) and a metallic taste when consuming carbonated beverages. * **Contraindication:** Avoid in patients with severe **sulfonamide allergy**. * **Dexamethasone:** Used as an alternative for prophylaxis in those allergic to sulfa drugs or for treating High-Altitude Cerebral Edema (HACE).

Q: Which of the following drugs act through heptahelical (serpentine) receptors?

Salbutamol. **Explanation:** The question tests your knowledge of receptor classification. **Heptahelical receptors**, also known as **G-Protein Coupled Receptors (GPCRs)** or **serpentine receptors**, are characterized by a single polypeptide chain that traverses the cell membrane seven times. **1. Why Salbutamol is Correct:** Salbutamol is a selective $\beta_2$-adrenergic agonist. All adrenergic receptors ($\alpha$ and $\beta$) belong to the **GPCR family**. Specifically, $\beta_2$ receptors are coupled with the **$G_s$ protein**, which activates adenylyl cyclase, increases intracellular cAMP, and leads to bronchodilation. **2. Why the other options are incorrect:** * **Insulin (Option A):** Acts through **Enzyme-linked receptors** (specifically, Receptor Tyrosine Kinase). Binding triggers autophosphorylation of tyrosine residues. * **Estrogen (Option B):** Being a steroid hormone, it is lipid-soluble and acts through **Intracellular (Nuclear) receptors**. It regulates gene transcription in the nucleus. * **Local Anaesthetics (Option C):** These do not act through metabotropic receptors; they work by physically blocking **Voltage-gated Sodium Channels** from the inner surface of the neuronal membrane, preventing depolarization. **High-Yield Clinical Pearls for NEET-PG:** * **GPCRs** are the largest family of cell surface receptors and the target of approximately 40-50% of all modern drugs. * **G-protein subtypes:** Remember **"QIS"** (Kiss) for Adrenergic receptors: $\alpha_1=G_q$, $\alpha_2=G_i$, $\beta=G_s$. * **Fastest receptors:** Ionotropic (Ligand-gated ion channels, e.g., Nicotinic ACh receptors). * **Slowest receptors:** Nuclear receptors (take hours to days to show effects via protein synthesis).

Q: Which of the following can reverse one or more smooth muscle effects of circulating histamine in humans?

Adrenaline. **Explanation:** The correct answer is **Adrenaline** because it acts as a **physiological antagonist** to histamine. While histamine causes bronchoconstriction and vasodilation (leading to hypotension) by acting on $H_1$ receptors, adrenaline acts on different receptors ($\beta_2$ and $\alpha_1$) to produce the exact opposite physiological effects: bronchodilation and vasoconstriction. This makes adrenaline the drug of choice for anaphylaxis, as it rapidly reverses the life-threatening smooth muscle effects of histamine regardless of the receptor involved. **Analysis of Incorrect Options:** * **Granisetron:** This is a selective **$5-HT_3$ receptor antagonist** used primarily as an antiemetic. It has no significant effect on histamine receptors or histamine-induced smooth muscle contraction. * **Ranitidine:** This is an **$H_2$ receptor blocker**. While it blocks histamine-induced gastric acid secretion, $H_2$ receptors have a minimal role in smooth muscle contraction compared to $H_1$ receptors. It cannot reverse systemic effects like bronchospasm. * **Sumatriptan:** This is a **$5-HT_{1B/1D}$ agonist** used in migraines to cause cranial vasoconstriction. It does not antagonize histamine's actions on systemic smooth muscles. **NEET-PG High-Yield Pearls:** * **Physiological Antagonism:** Two drugs acting on different receptors to produce opposite effects on the same physiological system (e.g., Adrenaline vs. Histamine, Insulin vs. Glucagon). * **Pharmacological Antagonism:** Competitive or non-competitive binding to the *same* receptor (e.g., Atropine vs. Acetylcholine). * **Clinical Note:** In anaphylactic shock, adrenaline is administered **Intramuscularly (IM)** in a **1:1000** concentration. It is the only drug that can reverse the "distributive shock" and "respiratory distress" caused by massive histamine release.

Question 1

What term describes drugs or biological products used for the diagnosis, treatment, or prevention of a rare disease or condition?

Accepted Answer

Orphan drugs

Answer

Rare drugs

Answer

Extinct drugs

Answer

Essential drugs

Question 2

Which of the following receptors has an intrinsic ion channel?

Accepted Answer

GABA A receptor

Answer

Insulin receptor

Answer

Vitamin A receptor

Answer

GABA B receptor

Question 3

Which of the following drugs can be accumulated in the fetus in a very significant amount if given to the pregnant mother?

Accepted Answer

Lignocaine

Answer

Thiopentone

Answer

Propofol

Answer

Midazolam

Question 4

Which of the following is an enzyme inhibitor?

Accepted Answer

Disulfiram

Answer

Phenobarbitone

Answer

Phenytoin

Answer

Carbon tetrachloride

Question 5

All the following drugs cross the blood-brain barrier EXCEPT one?

Accepted Answer

Dopamine

Answer

Morphine

Answer

Propranolol

Answer

Ether

Question 6

Which drug can directly release histamine from mast cells without involving an antigen-antibody reaction?

Accepted Answer

All of the above

Answer

d-tubocurarine

Answer

morphine

Answer

vancomycin

Question 7

What is the drug of choice for mountain sickness?

Accepted Answer

Acetazolamide

Answer

Cinnarizine

Answer

Furosemide

Answer

Betahistine

Question 8

Which of the following drugs act through heptahelical (serpentine) receptors?

Accepted Answer

Salbutamol

Answer

Insulin

Answer

Estrogen

Answer

Local anaesthetics

Question 9

Which of the following can reverse one or more smooth muscle effects of circulating histamine in humans?

Accepted Answer

Adrenaline

Answer

Granisetron

Answer

Ranitidine

Answer

Sumatriptan

Question 10

All of the following are properties of local anesthetics EXCEPT?

Accepted Answer

Preferential binding to resting channels

Answer

Blockade of voltage-dependent Na+ channels

Answer

Slowing of axonal impulse conduction

Answer

Increase in the membrane refractory period

General Pharmacology — MCQs

General Pharmacology — MCQs

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