General Pharmacology — MCQs

General Pharmacology Indian Medical PG Practice Questions and MCQs

Question 231: A newborn developed cleft lip, cleft palate, and atrial septal defect. Which of the following drugs, if consumed by the mother during pregnancy, is most likely to cause these congenital anomalies?

A. Digoxin
B. Methanol
C. ACE Inhibitors
D. Isotretinoin (Correct Answer)

Explanation: **Explanation:** The correct answer is **Isotretinoin (Option D)**. Isotretinoin, a vitamin A derivative used for severe acne, is one of the most potent human teratogens. It interferes with neural crest cell migration and HOX gene expression during embryogenesis. Exposure during the first trimester leads to **"Retinoic Acid Embryopathy,"** characterized by craniofacial abnormalities (cleft lip/palate, microtia), CNS defects, and cardiovascular malformations like Atrial Septal Defect (ASD) or Tetralogy of Fallot. **Analysis of Incorrect Options:** * **Digoxin (A):** It is generally considered safe during pregnancy and is often the drug of choice for treating fetal supraventricular tachycardia. It is not associated with structural malformations. * **Methanol (B):** While toxic to the mother (causing metabolic acidosis and blindness), it is not a classic teratogen associated with this specific triad of structural defects. Ethanol, however, causes Fetal Alcohol Syndrome (maxillary hypoplasia, smooth philtrum). * **ACE Inhibitors (C):** These are contraindicated in the 2nd and 3rd trimesters. They cause **"ACEI Fetopathy,"** characterized by renal dysgenesis, oligohydramnios, and skull hypoplasia, rather than first-trimester structural clefts. **NEET-PG High-Yield Pearls:** * **Isotretinoin Rule:** Female patients must follow the **iPLEDGE program**: two forms of contraception and two negative pregnancy tests before starting therapy. * **Critical Period:** The heart and face develop between weeks 3–8; this is the period of maximum teratogenic risk. * **Other Retinoid Facts:** Etretinate has a very long half-life (120 days); pregnancy should be avoided for 3 years after discontinuation.

Question 232: In drug metabolism, what is the primary role of the hepatic cytochrome P-450 system?

A. Mediating Phase I reactions such as hydrolysis, oxidation, and reduction. (Correct Answer)
B. Mediating Phase II reactions such as conjugation and synthesis.
C. Mediating both Phase I and Phase II reactions.
D. Converting hydrophilic metabolites into lipophilic metabolites.

Explanation: Drug metabolism (biotransformation) primarily occurs in the liver [2] to convert lipophilic drugs into polar, hydrophilic metabolites for easier excretion [1]. **1. Why Option A is correct:** The **Cytochrome P-450 (CYP450)** system is a superfamily of heme-containing enzymes located in the smooth endoplasmic reticulum (microsomes) [1]. Its primary role is to catalyze **Phase I reactions**, which include **oxidation** (most common), **reduction**, and **hydrolysis** [1]. These reactions introduce or expose a functional group (e.g., -OH, -NH2, -SH) to make the molecule more reactive [1]. **2. Why other options are incorrect:** * **Option B:** Phase II reactions involve **conjugation** (e.g., glucuronidation, acetylation, sulfation). These are generally mediated by non-P450 enzymes like UDP-glucuronosyltransferases (UGT). * **Option C:** While some enzymes overlap, the CYP450 system is specifically the hallmark of Phase I. Phase II is distinct and usually follows Phase I. * **Option D:** The goal of metabolism is the opposite—converting **lipophilic** drugs into **hydrophilic** (water-soluble) metabolites to prevent reabsorption in the renal tubules. **High-Yield NEET-PG Pearls:** * **CYP3A4:** The most abundant isoform, responsible for metabolizing ~50% of all clinical drugs. * **Enzyme Inducers (GPRS Cell Phone):** **G**riseofulvin, **P**henytoin, **R**ifampampicin, **S**moking, **C**arbamazepine, **P**henobarbitone. * **Enzyme Inhibitors (VITAMIN K):** **V**erapamil, **I**soniazid, **T**roleandomycin, **A**miodarone, **M**acrolides (except Azithromycin), **I**traconazole, **N**ight (Grapefruit) juice, **K**etoconazole. * **Microsomal vs. Non-microsomal:** CYP450 is microsomal. Glucuronidation is the *only* Phase II reaction that is microsomal; all other Phase II reactions are non-microsomal (cytosolic).

Question 233: What does the term "bioavailability" mean?

A. Plasma protein binding degree of substance
B. Permeability through the brain-blood barrier
C. Fraction of an unchanged drug reaching the systemic circulation following any route of administration (Correct Answer)
D. Amount of a substance in urine relative to the initial dose

Explanation: **Explanation:** **Bioavailability (F)** is defined as the rate and extent to which the active moiety (unchanged drug) enters the systemic circulation. When a drug is given intravenously, its bioavailability is 100% ($F=1$). For other routes (like oral), bioavailability is often less than 100% due to incomplete absorption and **first-pass metabolism** in the gut wall or liver. **Analysis of Options:** * **Option C (Correct):** This aligns with the standard pharmacological definition. It emphasizes that the drug must reach the "systemic circulation" in its "unchanged" (active) form to be bioavailable. * **Option A (Incorrect):** This refers to **Plasma Protein Binding**, which affects the drug's distribution and half-life, not its initial entry into the circulation. * **Option B (Incorrect):** This refers to **Blood-Brain Barrier (BBB) permeability**, a factor of lipid solubility that determines CNS penetration, not systemic bioavailability. * **Option D (Incorrect):** This relates to **Excretion** or clearance. Bioavailability is an absorption-related parameter, not an elimination-related one. **High-Yield NEET-PG Pearls:** 1. **Calculation:** Bioavailability is calculated by comparing the **Area Under the Curve (AUC)** of the oral route to the AUC of the IV route: $F = \frac{AUC_{oral}}{AUC_{IV}} \times 100$. 2. **Bioequivalence:** Two pharmaceutical formulations are "bioequivalent" if they show similar bioavailability (rate and extent of absorption) when given at the same dose. 3. **First-Pass Effect:** Drugs with high first-pass metabolism (e.g., Nitroglycerin, Propranolol, Lidocaine) have very low oral bioavailability and are usually given via alternative routes (sublingual, IV).

Question 234: Zero-order kinetics occur in which of the following drugs at high doses?

A. Phenytoin and Theophylline (Correct Answer)
B. Digoxin and Propranolol
C. Amiloride and Probenecid
D. Lithium and Theophylline

Explanation: ### Explanation **1. Understanding Zero-Order Kinetics** Most drugs follow **First-Order Kinetics**, where a constant *fraction* of the drug is eliminated per unit of time (rate is proportional to plasma concentration). However, some drugs follow **Zero-Order Kinetics** (Non-linear kinetics), where a constant *amount* of the drug is eliminated per unit of time, regardless of concentration. This occurs because the metabolic enzymes or transport systems become **saturated**. **Phenytoin** and **Theophylline** are classic examples of drugs that exhibit "Michaelis-Menten kinetics." At low therapeutic doses, they follow first-order kinetics, but as doses increase and metabolic pathways saturate, they shift to zero-order kinetics. This shift is clinically dangerous because a small increase in dose can lead to a disproportionately large increase in plasma concentration and toxicity. **2. Analysis of Incorrect Options** * **Option B:** **Digoxin** and **Propranolol** follow first-order kinetics. Propranolol has high first-pass metabolism, but its elimination rate remains proportional to its concentration. * **Option C:** **Amiloride** (diuretic) and **Probenecid** (uricosuric) follow first-order kinetics. * **Option D:** While **Theophylline** is correct, **Lithium** follows first-order kinetics and is primarily excreted unchanged by the kidneys. **3. NEET-PG High-Yield Pearls** To remember drugs following Zero-Order Kinetics, use the mnemonic **"ZERO WATTS"**: * **W:** Warfarin (at very high doses) * **A:** Alcohol (Ethanol) - *The most common example* * **T:** Theophylline / Tolbutamide * **T:** T-Salicylates (Aspirin) * **S:** Specific drugs like Phenytoin **Key Concept:** In zero-order kinetics, the **half-life ($t_{1/2}$) is not constant**; it increases as the plasma concentration increases. This makes therapeutic drug monitoring (TDM) essential for Phenytoin and Theophylline.

Question 235: Which muscle is affected last by d-tubocurarine?

A. Facial muscles
B. Diaphragm (Correct Answer)
C. Ocular muscles
D. Abdominal muscles

Explanation: ### Explanation The sequence of muscle paralysis by competitive neuromuscular blockers (like **d-tubocurarine**) follows a specific pattern based on muscle size, blood flow, and metabolic activity. **1. Why the Diaphragm is correct:** The **diaphragm** is the most resistant muscle to non-depolarizing neuromuscular blockers. It has a high density of nicotinic receptors and a very high blood flow, which allows it to maintain function longer than peripheral muscles. Consequently, it is the **last muscle to be paralyzed** and the **first to recover** once the drug effects wear off. This is a crucial safety mechanism in anesthesia. **2. Analysis of Incorrect Options:** * **C. Ocular muscles:** These are the **first** to be affected. Small, rapidly moving muscles (like those of the eyes, fingers, and jaw) are highly sensitive to blockade. * **A. Facial muscles:** These are affected shortly after the ocular muscles, following the "small-to-large" muscle progression. * **D. Abdominal muscles:** These are large trunk muscles. While they are paralyzed before the diaphragm, they are affected later than the small muscles of the face and limbs. **3. NEET-PG High-Yield Pearls:** * **Sequence of Paralysis:** Small muscles (Eyes/Face) → Limbs/Trunk → Intercostal muscles → Diaphragm. * **Sequence of Recovery:** Exactly the reverse (Diaphragm recovers first). * **Mechanism:** d-tubocurarine is a prototype non-depolarizing blocker that acts as a competitive antagonist at **Nm receptors**. * **Clinical Sign:** "Curarization" refers to the state of paralysis; "Decurarization" is the reversal, typically achieved using an acetylcholinesterase inhibitor like **Neostigmine** (combined with Glycopyrrolate to prevent muscarinic side effects).

Question 236: Which of the following monoclonal antibodies is a humanized antibody?

A. Rituximab
B. Palivizumab (Correct Answer)
C. Infliximab
D. Basilximab

Explanation: The nomenclature of monoclonal antibodies (mAbs) is a high-yield topic for NEET-PG. The origin of an antibody is determined by the **source substem** (the letters immediately preceding the suffix "-mab"). ### **1. Why Palivizumab is Correct** The substem **"-zu-"** indicates a **Humanized** antibody. These are approximately 95% human and 5% murine (mouse). The CDR (complementarity-determining regions) are derived from mice, while the rest of the immunoglobulin molecule is human. * **Palivizumab:** Used for the prevention of Respiratory Syncytial Virus (RSV) infections in high-risk infants. ### **2. Analysis of Incorrect Options** * **Rituximab (Option A):** Contains the substem **"-xi-"**, which stands for **Chimeric** antibody (~65% human). It targets CD20 and is used in Non-Hodgkin Lymphoma and Rheumatoid Arthritis. * **Infliximab (Option C):** Also a **Chimeric** antibody (**"-xi-"**). It is a TNF-alpha inhibitor used in Crohn’s disease and Ulcerative Colitis. * **Basiliximab (Option D):** A **Chimeric** antibody (**"-xi-"**). It is an IL-2 receptor antagonist used to prevent acute organ transplant rejection. ### **3. High-Yield Clinical Pearls for NEET-PG** To quickly identify the source of any mAb, remember these substems: * **-omab:** 100% Mouse (Murine) – e.g., Muromonab. * **-ximab:** Chimeric (Mixed) – e.g., Rituximab, Cetuximab. * **-zumab:** Humani**z**ed – e.g., Trastu**z**umab, Beva**z**izumab. * **-umab:** 100% H**u**man – e.g., Adalim**u**mab, Panitum**u**mab. **Note:** Humanized and Human antibodies have lower immunogenicity and a lower risk of infusion reactions compared to chimeric or murine antibodies.

Question 237: Which of the following is a muscle relaxant?

A. Scoline (Correct Answer)
B. Pentazocine
C. Hyoscine
D. Phenylephrine

Explanation: **Explanation:** **Scoline (Suxamethonium/Succinylcholine)** is the correct answer. It is a **depolarizing neuromuscular blocking agent** used as a skeletal muscle relaxant. It works by mimicking the action of acetylcholine at the nicotinic receptors ($N_m$) of the neuromuscular junction, causing persistent depolarization which leads to transient fasciculations followed by flaccid paralysis. It is the drug of choice for rapid sequence intubation due to its rapid onset (30–60 seconds) and short duration of action (5–10 minutes). **Analysis of Incorrect Options:** * **Pentazocine:** An opioid analgesic with mixed agonist-antagonist properties (Kappa agonist and Mu antagonist/partial agonist). It is used for moderate to severe pain, not muscle relaxation. * **Hyoscine (Scopolamine):** An anticholinergic (muscarinic antagonist). It is primarily used for motion sickness, as a pre-anesthetic medication to reduce secretions, and for intestinal colic. * **Phenylephrine:** A selective $\alpha_1$-adrenergic agonist. It acts as a potent vasoconstrictor and nasal decongestant; it is also used as a mydriatic. **High-Yield Clinical Pearls for NEET-PG:** * **Metabolism:** Scoline is rapidly hydrolyzed by **pseudocholinesterase** (butyrylcholinesterase). Patients with a genetic deficiency of this enzyme may experience prolonged apnea (**Scoline Apnea**). * **Side Effects:** Hyperkalemia (caution in burn/trauma patients), malignant hyperthermia (treated with **Dantrolene**), and post-operative muscle myalgia. * **Phase II Block:** Prolonged exposure to Scoline can lead to a non-depolarizing-like block, known as a Phase II block.

Question 238: What is the primary objective of Phase II in a clinical drug trial?

A. Human pharmacology and safety assessment
B. Therapeutic exploration and dose ranging (Correct Answer)
C. Therapeutic comparison with existing treatments
D. Post-marketing surveillance and monitoring

Explanation: ### Explanation **Phase II** of a clinical trial is primarily focused on **Therapeutic Exploration**. After Phase I confirms safety in healthy volunteers, Phase II involves a small group of patients (100–300) suffering from the target disease. The primary objectives are to evaluate **efficacy**, establish the **dose-response relationship**, and determine the optimal dose range for larger trials. #### Analysis of Options: * **Option B (Correct):** Phase II aims to see if the drug actually works in patients (efficacy) and identifies the minimum effective dose and maximum tolerated dose (**dose-ranging**). * **Option A (Incorrect):** This describes **Phase I**. Phase I focuses on human pharmacology, safety, and pharmacokinetics, typically conducted in healthy volunteers (except for toxic drugs like anti-cancer agents). * **Option C (Incorrect):** This describes **Phase III (Therapeutic Confirmation)**. Phase III involves large-scale multicentric trials to compare the new drug against existing "gold standard" treatments or placebos to confirm clinical benefit. * **Option D (Incorrect):** This describes **Phase IV (Post-marketing Surveillance)**. It occurs after the drug is marketed to detect rare long-term adverse effects and monitor performance in the general population. #### High-Yield NEET-PG Pearls: * **Phase 0:** Also called **Microdosing** studies; uses sub-therapeutic doses to study pharmacokinetics (PK) without pharmacological effects. * **Phase I:** First stage in humans; focuses on **Safety** and **Tolerability**. * **Phase II:** Divided into **IIa** (pilot study for efficacy) and **IIb** (pivotal study for dose-finding). This phase has the highest failure rate in drug development. * **Phase III:** Required for **Marketing Authorization** (NDA filing). * **Phase IV:** Identifies **Rare Adverse Events** (e.g., Phocomelia, Rofecoxib-induced cardiotoxicity).

Question 239: Hemodialysis is useful in all of the following conditions except:

A. Barbiturate poisoning
B. Methanol poisoning
C. Salicylate poisoning (Correct Answer)
D. Digoxin poisoning

Explanation: **Explanation:** The effectiveness of hemodialysis (HD) in treating poisoning depends on specific pharmacokinetic properties of the toxin. For a drug to be dialyzable, it must have a **low molecular weight, low volume of distribution (Vd), and low plasma protein binding.** **Why Digoxin is the Correct Answer (Exception):** Digoxin has an extremely **large Volume of Distribution (Vd > 5-7 L/kg)** because it binds extensively to cardiac and skeletal muscle tissues. Only a tiny fraction of the drug remains in the plasma to be filtered by the dialysis machine. Therefore, hemodialysis is ineffective. The treatment of choice for severe digoxin toxicity is **Digoxin-specific antibody fragments (DigiFab).** *Note: There appears to be a typographical error in the provided key. While the question asks for the "except" (ineffective) condition, Salicylates are actually highly dialyzable. Digoxin is the classic "non-dialyzable" drug.* **Analysis of Other Options:** * **Salicylate Poisoning:** HD is the treatment of choice for severe aspirin toxicity (levels >100 mg/dL) because salicylates have a low Vd [1] and are small molecules. * **Methanol Poisoning:** Methanol is a small, water-soluble molecule. HD effectively removes both methanol and its toxic metabolite, formic acid. * **Barbiturate Poisoning:** Long-acting barbiturates (like Phenobarbital) have low protein binding and low Vd [1], making them amenable to removal via HD or hemoperfusion. **NEET-PG High-Yield Pearls:** * **Mnemonic for Dialyzable drugs (BLAST-M):** **B**arbiturates (Long-acting), **L**ithium, **A**lcohol (Methanol/Ethanol), **S**alicylates, **T**heophylline, **M**etformin [1]. * **Drugs NOT removed by HD:** Digoxin, Benzodiazepines, Opioids, Tricyclic Antidepressants (TCAs), and Calcium Channel Blockers (due to high Vd or high protein binding) [1].

Question 240: All of the following are true regarding lidocaine except:

A. It acts on sodium channels in both active and inactive states.
B. It is the most cardiotoxic local anesthetic. (Correct Answer)
C. It is given intravenously for cardiac arrhythmias.
D. It undergoes extensive first-pass metabolism.

Explanation: **Explanation:** **Why Option B is the correct answer (The "Except" statement):** Lidocaine is actually known for its relatively low cardiotoxicity compared to other local anesthetics. **Bupivacaine** is the most cardiotoxic local anesthetic; it binds more tightly to sodium channels during diastole ("slow-in, slow-out" kinetics), making resuscitation from bupivacaine-induced cardiac arrest extremely difficult. Lidocaine, conversely, dissociates rapidly from the channels. **Analysis of other options:** * **Option A:** Local anesthetics like lidocaine follow the "state-dependent blockade" principle. They have a higher affinity for sodium channels in the **active** (open) and **inactive** (refractory) states rather than the resting state. * **Option C:** Lidocaine is a **Class IB anti-arrhythmic**. It is administered intravenously to treat ventricular arrhythmias, particularly those associated with acute myocardial infarction or cardiac surgery. * **Option D:** Lidocaine undergoes **extensive first-pass metabolism** in the liver (extraction ratio >0.7). Therefore, it cannot be administered orally for systemic effects and requires parenteral administration. **NEET-PG High-Yield Pearls:** * **Drug of Choice:** Lidocaine is the most widely used local anesthetic due to its rapid onset and intermediate duration of action. * **Bupivacaine Toxicity:** If bupivacaine toxicity occurs, the antidote is **Intravenous Lipid Emulsion (20% Intralipid)**. * **Metabolism:** Lidocaine is metabolized by hepatic CYP1A2 to active metabolites (MEGX and glycine xylidide), which can contribute to toxicity (seizures). * **Adrenaline Co-administration:** Often added to lidocaine to cause vasoconstriction, which decreases systemic absorption, reduces toxicity, and prolongs the duration of the block.

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