General Pharmacology — MCQs

General Pharmacology Indian Medical PG Practice Questions and MCQs

Question 61: Volume of distribution of a drug is given by?

A. Vd = Dose administered i.v. / Plasma concentration (Correct Answer)
B. Vd = Maximum tolerated dose / Dose administered i.v.
C. Vd = Dose administered i.v. / Total lipid solubility
D. Vd = t 1/2 / Dose administered i.v.

Explanation: **Explanation:** **1. Why Option A is Correct:** The **Apparent Volume of Distribution (Vd)** is a theoretical volume that relates the total amount of drug in the body to the concentration of the drug measured in the plasma. It is calculated using the formula: **Vd = Total amount of drug in the body (Dose) / Plasma concentration (C)** When a drug is administered intravenously (i.v.), the entire dose enters the systemic circulation immediately. Therefore, Vd represents the space required to contain the drug if it were distributed homogeneously at the same concentration found in the plasma. **2. Why Other Options are Incorrect:** * **Option B:** This describes a ratio related to the Therapeutic Index or safety margin, not distribution. * **Option C:** While lipid solubility *influences* Vd (high lipid solubility usually leads to a high Vd), it is not a mathematical component of the formula. * **Option D:** This is a distractor. While Vd is used to calculate half-life ($t_{1/2} = 0.693 \times Vd / CL$), the formula provided is mathematically incorrect. **3. NEET-PG High-Yield Clinical Pearls:** * **Loading Dose:** Vd is the primary determinant of the loading dose ($LD = Vd \times Target\ Plasma\ Concentration$). * **Low Vd (< 5L):** Indicates the drug is confined to the vascular compartment (e.g., **Warfarin, Heparin**). * **High Vd (> 40L):** Indicates the drug is sequestered in peripheral tissues/fat (e.g., **Chloroquine, Digoxin**). * **Dialysis:** Drugs with a high Vd cannot be efficiently removed by hemodialysis because most of the drug is outside the plasma. * **Plasma Protein Binding:** Drugs with high plasma protein binding tend to have lower Vd.

Question 62: Which drug is never given by the oral route?

A. Erythromycin
B. Ciprofloxacin
C. Streptomycin (Correct Answer)
D. Albendazole

Explanation: **Explanation:** The correct answer is **Streptomycin**. **Why Streptomycin?** Streptomycin is an **Aminoglycoside**. Chemically, aminoglycosides are highly polar, polycationic compounds. Due to this high polarity, they are **not absorbed from the gastrointestinal tract (GIT)**. If administered orally, they remain in the gut lumen and are excreted unchanged in the feces. Therefore, for systemic infections (like Tuberculosis or Plague), Streptomycin must be administered via the **intramuscular (IM)** route. **Analysis of Incorrect Options:** * **Erythromycin (Option A):** This is a Macrolide antibiotic. While it is acid-labile, it is formulated as enteric-coated tablets or stable esters (e.g., Erythromycin stearate) to allow effective oral absorption. * **Ciprofloxacin (Option B):** This is a Fluoroquinolone with excellent oral bioavailability (approx. 70%). It is one of the most commonly prescribed oral antibiotics for UTIs and RTIs. * **Albendazole (Option C):** This antihelminthic is primarily given orally. Interestingly, it is taken on an empty stomach for intraluminal parasites (poor absorption) and with a fatty meal when systemic absorption is required (e.g., Neurocysticercosis). **NEET-PG High-Yield Pearls:** 1. **Exceptions for Oral Aminoglycosides:** While not used for systemic infections, oral Neomycin and Kanamycin are used for **"Gut Sterilization"** before bowel surgery and in **Hepatic Encephalopathy** to reduce ammonia-producing bacteria. 2. **The "Big Three" Non-Absorbables:** Remember that Aminoglycosides, Vancomycin (except for *C. difficile* colitis), and Amphotericin B are generally not absorbed orally due to their large or polar structures. 3. **Streptomycin Side Effects:** Always monitor for **Ototoxicity** (vestibular damage) and **Nephrotoxicity** in patients on this drug.

Question 63: Which of the following are examples of physiological antagonism?

A. Adrenaline and salbutamol
B. Adrenaline and histamine
C. Salbutamol and leukotrienes
D. Both B and C (Correct Answer)

Explanation: ### Explanation **Concept of Physiological Antagonism** Physiological (or functional) antagonism occurs when two drugs act on **different receptors** and produce **opposing physiological effects** on the same effector organ or system. Unlike pharmacological antagonism, they do not compete for the same receptor site. **Why Option D (Both B and C) is Correct:** * **Adrenaline and Histamine (Option B):** This is the classic textbook example. Histamine acts on **H₁ receptors** causing bronchoconstriction and vasodilation. Adrenaline acts on **β₂ receptors** (bronchodilation) and **α₁ receptors** (vasoconstriction). Because they produce opposite effects via different receptors, adrenaline is the physiological antagonist of histamine and is the drug of choice for anaphylactic shock. * **Salbutamol and Leukotrienes (Option C):** Leukotrienes (e.g., LTC4, LTD4) act on **CysLT₁ receptors** to cause potent bronchoconstriction. Salbutamol acts on **β₂ receptors** to cause bronchodilation. Since they act on different receptors to produce opposite effects on bronchial smooth muscle, they are physiological antagonists. **Why Option A is Incorrect:** * **Adrenaline and Salbutamol:** Both drugs are **agonists** at the β₂-adrenergic receptor. They produce synergistic (additive) effects on bronchodilation rather than opposing each other. **NEET-PG High-Yield Pearls:** * **Chemical Antagonism:** Occurs when two drugs react chemically in solution (e.g., Heparin and Protamine sulfate; Chelating agents and heavy metals). * **Pharmacological Antagonism:** Occurs at the same receptor (e.g., Atropine and Acetylcholine at Muscarinic receptors). * **Clinical Application:** Adrenaline is used in anaphylaxis because it works instantly via physiological antagonism, bypassing the histamine receptor blockade which would be too slow.

Question 64: Which of the following is a second-generation H1 antihistamine?

A. Cetirizine (Correct Answer)
B. Promethazine
C. Cinnarizine
D. Pheniramine

Explanation: **Explanation:** The correct answer is **Cetirizine**. H1 antihistamines are classified into two generations based on their ability to cross the blood-brain barrier (BBB) and their sedative potential. **1. Why Cetirizine is correct:** Cetirizine is a **second-generation H1 antihistamine**. These drugs are highly polar, have low lipid solubility, and are substrates for the P-glycoprotein efflux pump. Consequently, they do not cross the BBB significantly, making them **non-sedating**. They also have a longer duration of action and minimal anticholinergic effects compared to the first generation. **2. Why the other options are incorrect:** * **Promethazine (Option B):** A first-generation antihistamine known for its strong sedative and antiemetic properties. It is frequently used for motion sickness and preoperative sedation. * **Cinnarizine (Option C):** A first-generation antihistamine with calcium channel blocking activity. It is primarily used for vertigo and labyrinthine disorders. * **Pheniramine (Option D):** A classic first-generation antihistamine (commonly known as Avil) used for allergic rhinitis and urticaria, but it causes significant drowsiness. **High-Yield Clinical Pearls for NEET-PG:** * **Active Metabolites:** Cetirizine is the active metabolite of Hydroxyzine; Fexofenadine is the active metabolite of Terfenadine; Loratadine is metabolized to Desloratadine. * **Safety Profile:** Fexofenadine is considered the "least sedating" antihistamine and is the drug of choice for pilots/drivers. * **Cardiac Warning:** Terfenadine and Astemizole (older 2nd gen) were withdrawn due to the risk of **QT prolongation and Torsades de Pointes**, especially when co-administered with CYP3A4 inhibitors (e.g., Erythromycin, Ketoconazole). * **Topical 2nd Gen:** Azelastine and Olopatadine are used as nasal sprays or eye drops for allergic rhinitis/conjunctivitis.

Question 65: Which one of the following statements regarding drug effects on serotonin receptor systems is accurate?

A. 5HT2 receptor blockers counteract bronchoconstriction and diarrhea of carcinoid. (Correct Answer)
B. Sumatriptan is an antiemetic because it blocks 5HT3 receptors.
C. MAO type B inhibitors lead to increased levels of serotonin in the CNS.
D. Ondansetron is used in migraine because it activates 5HT1D receptors.

Explanation: ### Explanation **1. Why Option A is Correct:** Carcinoid syndrome is characterized by the excessive release of serotonin (5-HT) from neuroendocrine tumors. This excess 5-HT acts on **5-HT₂ receptors** to cause smooth muscle contraction, leading to clinical manifestations like **bronchoconstriction** and hypermotility of the gut (**diarrhea**). 5-HT₂ receptor antagonists (such as **Cyproheptadine**) are clinically used to manage these symptoms by blocking the peripheral effects of serotonin. **2. Why the Other Options are Incorrect:** * **Option B:** Sumatriptan is a **5-HT₁B/₁D agonist** used in the acute treatment of migraine. It causes vasoconstriction of cranial vessels. It is *not* an antiemetic. * **Option C:** Serotonin is primarily metabolized by **MAO-A**. Therefore, MAO-A inhibitors (not MAO-B) lead to increased CNS serotonin levels. MAO-B inhibitors (e.g., Selegiline) primarily increase dopamine levels and are used in Parkinson’s disease. * **Option D:** Ondansetron is a **5-HT₃ receptor antagonist**. It is used as a potent **antiemetic** (especially for chemotherapy-induced nausea), not for migraine. **3. High-Yield Clinical Pearls for NEET-PG:** * **Cyproheptadine:** A 5-HT₂ blocker also used for appetite stimulation and treating **Serotonin Syndrome**. * **5-HT₃ Receptors:** The only serotonin receptors that are **ionotropic** (ligand-gated ion channels); all others are G-protein coupled (metabotropic). * **Triptans:** Contraindicated in patients with Ischemic Heart Disease (IHD) due to coronary vasospasm (5-HT₁B effect). * **Carcinoid Diagnosis:** Look for elevated **5-HIAA** (5-Hydroxyindoleacetic acid) in a 24-hour urine sample.

Question 66: Receptor agonists possess which of the following properties?

A. Affinity but no intrinsic activity
B. Intrinsic activity but no affinity
C. Affinity and intrinsic activity (Correct Answer)
D. Affinity and intrinsic activity with a negative effect

Explanation: To understand the mechanism of drug action, it is essential to distinguish between two key properties: **Affinity** (the ability of a drug to bind to a receptor) and **Intrinsic Activity** (the ability of the drug to trigger a biological response after binding). ### **Explanation of the Correct Answer** **Option C (Affinity and intrinsic activity)** is correct because a **Receptor Agonist** is a ligand that binds to a receptor and stabilizes it in a particular conformation (usually the active state) to produce a functional response. Therefore, it must possess both the ability to bind (Affinity) and the ability to activate the receptor (Intrinsic Activity). ### **Analysis of Incorrect Options** * **Option A (Affinity but no intrinsic activity):** This describes an **Antagonist**. Antagonists bind to the receptor (affinity) to block the action of an agonist but do not produce any biological response of their own (intrinsic activity = 0). * **Option B (Intrinsic activity but no affinity):** This is physiologically impossible. A drug cannot produce a receptor-mediated response without first binding to that receptor. * **Option C (Affinity and intrinsic activity with a negative effect):** This describes an **Inverse Agonist**. While they have affinity, they bind to constitutively active receptors to produce an effect opposite to that of a conventional agonist (intrinsic activity is between 0 and -1). ### **High-Yield NEET-PG Clinical Pearls** * **Intrinsic Activity (IA) Values:** * Full Agonist: IA = 1 * Partial Agonist: IA = Between 0 and 1 (acts as an antagonist in the presence of a full agonist). * Antagonist: IA = 0 * Inverse Agonist: IA = -1 * **Efficacy vs. Potency:** **Efficacy** (the maximum response a drug can produce) is determined by intrinsic activity, whereas **Potency** (the amount of drug needed for a response) is largely determined by affinity ($K_d$ value). * **Spare Receptors:** A full response can often be achieved by an agonist even when only a fraction of receptors are occupied; these "extra" receptors are termed spare receptors.

Question 67: What is the advantage of the sublingual route for drug administration?

A. It prevents or bypasses first-pass metabolism. (Correct Answer)
B. It is easy to administer.
C. The drug must be lipid-soluble.
D. It can be spit out if signs of toxicity appear.

Explanation: ### Explanation **Correct Option: A. It prevents or bypasses first-pass metabolism.** The sublingual route involves placing a drug under the tongue, where it dissolves and is absorbed directly through the oral mucosa into the systemic circulation via the **superior vena cava**. Unlike the oral route, the drug does not enter the portal circulation; therefore, it bypasses the liver (the primary site of first-pass metabolism). This ensures higher bioavailability and a rapid onset of action, making it ideal for emergencies like acute anginal attacks. **Analysis of Incorrect Options:** * **B. It is easy to administer:** While relatively simple, "ease of administration" is a subjective clinical convenience rather than a pharmacological advantage. The primary *pharmacokinetic* advantage is the bypass of hepatic metabolism. * **C. The drug must be lipid-soluble:** This is a **requirement** for the route to work, not an advantage. Only lipid-soluble, non-irritating drugs (e.g., Nitroglycerin, Buprenorphine) can diffuse across the lipid bilayer of the oral mucosa. * **D. It can be spit out if signs of toxicity appear:** While true that the drug can be removed to stop further absorption, this is a safety feature/precaution rather than the primary therapeutic advantage sought when choosing this route. **High-Yield Clinical Pearls for NEET-PG:** * **Nitroglycerin (GTN):** The classic example. It has very high first-pass metabolism (>90%), making the sublingual route essential for its efficacy in angina. * **Other Sublingual Drugs:** Buprenorphine (opioid), Desmopressin (analogue of ADH), and Nifedipine (though no longer preferred for hypertensive emergencies due to unpredictable BP drops). * **Key Concept:** Any drug absorbed from the mouth, pharynx, or rectum (partially) bypasses the liver, avoiding the "First-Pass Effect."

Question 68: Which of the following statements about fexofenadine is true?

A. It undergoes high first-pass metabolism in the liver.
B. Terfenadine is an active metabolite of this drug.
C. It does not block cardiac K+ channels. (Correct Answer)
D. It has high affinity for central H1 receptors.

Explanation: ### Explanation **Correct Answer: C. It does not block cardiac K+ channels.** **1. Why the Correct Answer is Right:** Fexofenadine is a second-generation H1 antihistamine. Its predecessor, **Terfenadine**, was notorious for blocking delayed rectifier potassium ($K^+$) channels in the heart, leading to QT interval prolongation and a life-threatening arrhythmia known as *Torsades de Pointes*. Fexofenadine, the active metabolite of terfenadine, retains the antihistaminic efficacy but **lacks the $K^+$ channel-blocking property**, making it cardiosafe. **2. Analysis of Incorrect Options:** * **Option A:** Fexofenadine does not undergo significant hepatic metabolism. It is primarily excreted unchanged in the feces and urine. * **Option B:** This is reversed. **Fexofenadine is the active metabolite of Terfenadine.** Terfenadine is a prodrug that is converted to fexofenadine by the CYP3A4 enzyme. * **Option D:** Fexofenadine is a second-generation antihistamine with **low lipid solubility** and is a substrate for the P-glycoprotein efflux pump. Consequently, it does not cross the blood-brain barrier effectively and has a **very low affinity for central H1 receptors**, making it non-sedating. **3. High-Yield Clinical Pearls for NEET-PG:** * **"The Safe Metabolite":** Fexofenadine was developed to avoid the drug-drug interactions seen with Terfenadine (e.g., when taken with Ketoconazole or Erythromycin, which inhibit CYP3A4, leading to toxic Terfenadine levels). * **Non-Sedating Profile:** Along with Loratadine and Cetirizine, Fexofenadine is preferred for patients in occupations requiring high alertness (e.g., pilots, drivers). * **Interaction:** Avoid taking fexofenadine with fruit juices (orange, grapefruit, apple) as they inhibit OATP1A2, reducing the drug's absorption.

Question 69: Which one of the following drugs does not undergo the first-pass effect?

A. Propranolol
B. Lidocaine
C. Insulin (Correct Answer)
D. Morphine

Explanation: ### Explanation **1. Why Insulin is the Correct Answer:** The **first-pass effect (presystemic metabolism)** refers to the phenomenon where a drug is metabolized in the gut wall or the liver before it reaches the systemic circulation. This occurs primarily with drugs administered **orally**. **Insulin** is a polypeptide hormone. If given orally, it would be degraded by gastrointestinal enzymes (proteolysis) and gastric acid, making it ineffective. Therefore, insulin is administered **parenterally** (subcutaneously or intravenously). By bypassing the enteral route and the portal circulation, insulin enters the systemic circulation directly, thus avoiding the first-pass effect. **2. Analysis of Incorrect Options:** * **Propranolol (Option A):** A classic example of a drug with high first-pass metabolism. Its oral bioavailability is low (~25%), requiring much higher oral doses compared to intravenous doses. * **Lidocaine (Option B):** Undergoes extensive first-pass metabolism (extraction ratio >0.7). It is almost entirely metabolized by the liver, which is why it is never given orally for cardiac arrhythmias. * **Morphine (Option C):** Significant first-pass metabolism occurs via glucuronidation in the liver. This explains why the parenteral dose is significantly lower than the oral dose for equivalent analgesia. **3. NEET-PG High-Yield Pearls:** * **Routes bypassing first-pass:** Sublingual, Transdermal, Parenteral (IV/SC/IM), and to a large extent, Inhalation. * **Rectal Route:** Bypasses approximately 50% of the first-pass effect (superior hemorrhoidal veins drain to the portal system, while inferior/middle drain to the systemic system). * **High First-Pass Drugs (Mnemonic: "LMP-ST"):** **L**idocaine, **M**orphine, **P**ropranolol, **S**albutamol, **T**ricyclic antidepressants (TCAs), and Nitroglycerin. * **Clinical Significance:** Drugs with high first-pass metabolism show marked individual variation in plasma concentrations and are sensitive to changes in hepatic blood flow.

Question 70: Which of the following is NOT a feature of depolarizing neuromuscular blocking agents?

A. Cause muscle fasciculations
B. No fade
C. No post-tetanic facilitation
D. Reversed by neostigmine (Correct Answer)

Explanation: ### Explanation Depolarizing neuromuscular blockers (DNMBs), primarily **Succinylcholine**, act as nicotinic acetylcholine receptor (nAChR) agonists. They mimic acetylcholine but persist longer at the synapse, causing prolonged depolarization of the motor endplate. **Why Option D is the Correct Answer:** Neostigmine is an acetylcholinesterase (AChE) inhibitor. By preventing the breakdown of endogenous acetylcholine (ACh), it increases ACh levels at the synaptic cleft. In the case of DNMBs, more ACh further depolarizes the already depolarized membrane, which **potentiates (worsens)** the block rather than reversing it. Neostigmine only reverses non-depolarizing blockers (like Vecuronium) by outcompeting them for the receptor. **Analysis of Incorrect Options:** * **A. Cause muscle fasciculations:** Before the flaccid paralysis sets in, the initial activation of nAChRs causes disorganized muscle contractions known as fasciculations. * **B. No fade:** During Train-of-Four (TOF) monitoring, DNMBs (Phase I block) show a constant diminished response in all four twitches. "Fade" (progressive weakening) is a hallmark of non-depolarizing agents. * **C. No post-tetanic facilitation:** In a Phase I block, tetanic stimulation does not lead to an increased release of ACh that can overcome the block; therefore, no enhancement of subsequent twitches is seen. **High-Yield Clinical Pearls for NEET-PG:** * **Phase II Block:** With prolonged infusion or high doses, Succinylcholine can show features of non-depolarizing blocks (fade and reversal by neostigmine). * **Metabolism:** Succinylcholine is rapidly hydrolyzed by **Pseudocholinesterase** (Butyrylcholinesterase). * **Key Side Effects:** Hyperkalemia (dangerous in burn/trauma patients), Malignant Hyperthermia (treated with **Dantrolene**), and muscle soreness. * **Drug of Choice:** For Rapid Sequence Induction (RSI) due to its fast onset and short duration.

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