NEET-PG 2013 — Pharmacology
143 Previous Year Questions with Answers & Explanations
Which of the following act through G protein coupled receptors?
Which of the following is not an ionic receptor?
Which of the following substances is not classified as a carcinogen for bladder cancer?
What is the mechanism of metabolism for alcohol, aspirin, and phenytoin at high doses?
Which of the following factors influences the duration of action of a drug?
Which route of administration undergoes the maximum first pass metabolism?
Which of the following drugs is known to have low first pass metabolism?
Which drug has the highest plasma protein binding?
In the context of pharmacology, which plasma protein do acidic drugs primarily bind to?
Microvesicular fatty liver is caused by ?
NEET-PG 2013 - Pharmacology NEET-PG Practice Questions and MCQs
Question 1: Which of the following act through G protein coupled receptors?
- A. Ach Muscarinic receptors (Correct Answer)
- B. Insulin receptors
- C. Ach Nicotinic receptors
- D. GABA-A receptors
Explanation: ***Ach Muscarinic receptors*** - All five **muscarinic acetylcholine receptors (M1-M5)** are **G protein-coupled receptors (GPCRs)** that mediate the parasympathetic nervous system's effects. - Activation of these receptors leads to downstream signaling through various G proteins, influencing cellular functions like heart rate and smooth muscle contraction. *Insulin receptors* - Insulin receptors are **receptor tyrosine kinases (RTKs)**, not GPCRs. - Upon insulin binding, they undergo autophosphorylation and activate intracellular signaling cascades involving **IRS proteins**, leading to glucose uptake. *Ach Nicotinic receptors* - Nicotinic acetylcholine receptors are **ligand-gated ion channels**, not GPCRs. - They open an ion pore in response to acetylcholine binding, allowing ions like sodium to flow through, resulting in rapid depolarization. *GABA-A receptors* - GABA-A receptors are also **ligand-gated ion channels**, specifically anion channels that are permeable to chloride ions. - When GABA binds, they open, allowing chloride influx, which typically hyperpolarizes the neuron and inhibits neural activity.
Question 2: Which of the following is not an ionic receptor?
- A. Kainate
- B. AMPA
- C. mGluR (Correct Answer)
- D. NMDA
Explanation: **Ionic receptors** (ionotropic receptors) are ligand-gated ion channels that open upon binding, allowing ions to flow directly through the channel. **Non-ionic receptors** (metabotropic receptors) are G-protein coupled receptors that activate intracellular signaling cascades. ***mGluR*** - **Metabotropic glutamate receptors (mGluRs)** are **G-protein coupled receptors** (GPCRs), meaning they activate intracellular signaling pathways rather than directly forming an ion channel. - Their activation leads to slower, longer-lasting changes in neuronal excitability through second messenger systems. - **This is the correct answer** as mGluRs are NOT ionic receptors. *NMDA* - **NMDA receptors** are **ionotropic glutamate receptors** that form ligand-gated ion channels permeable to calcium and sodium ions. - They are crucial for **synaptic plasticity** and learning. *Kainate* - **Kainate receptors** are also **ionotropic glutamate receptors** that are permeable to sodium and potassium ions. - They play diverse roles in synaptic transmission and neuronal excitability. *AMPA* - **AMPA receptors** are **ionotropic glutamate receptors** primarily responsible for fast excitatory synaptic transmission in the central nervous system. - They are permeable to sodium and potassium ions and mediate the majority of fast excitatory synaptic currents.
Question 3: Which of the following substances is not classified as a carcinogen for bladder cancer?
- A. Acrolein
- B. Phenacetin
- C. Benzidine
- D. Isopropyl alcohol (Correct Answer)
Explanation: ***Isopropyl alcohol*** - Research does not link **isopropyl alcohol** to an increased risk of bladder cancer, making it a non-carcinogenic substance in this context. - It is commonly used as a solvent and antiseptic, but has not shown **urogenic carcinogenicity** in studies. *Phenacetin* - **Phenacetin** is an analgesic that has been associated with an increased risk of bladder cancer, particularly due to its metabolite, which can be nephrotoxic. - Its use has significantly declined due to its carcinogenic effects on the urinary system. *Benzidine* - **Benzidine** is a well-known bladder carcinogen, primarily linked to the dye industry, where exposure has led to increased rates of bladder cancer [1]. - This substance has been implicated in **urothelial carcinoma** due to its mutagenic properties. *Acrolein* - **Acrolein** is a toxic compound that can cause bladder irritation and has been studied for its potential carcinogenic effects related to bladder cancer. - It is released during the combustion of materials and is known to contribute to **chemical injury** in the bladder. **References:** [1] Cross SS. Underwood's Pathology: A Clinical Approach. 6th ed. (Basic Pathology) introduces the student to key general principles of pathology, both as a medical science and as a clinical activity with a vital role in patient care. Part 2 (Disease Mechanisms) provides fundamental knowledge about the cellular and molecular processes involved in diseases, providing the rationale for their treatment. Part 3 (Systematic Pathology) deals in detail with specific diseases, with emphasis on the clinically important aspects., pp. 217-218.
Question 4: What is the mechanism of metabolism for alcohol, aspirin, and phenytoin at high doses?
- A. First pass kinetics
- B. First order kinetics
- C. Zero order kinetics (Correct Answer)
- D. Second order kinetics
Explanation: ***Zero order kinetics*** - This mechanism occurs when the **metabolic enzymes become saturated at high drug concentrations**, leading to a constant amount (not a constant percentage) of drug being eliminated per unit time. - Alcohol, aspirin, and phenytoin are examples of drugs that exhibit **saturable metabolism**, transitioning from first-order to zero-order kinetics at higher doses. *First pass kinetics* - This describes the **metabolism of a drug by the liver or gut wall enzymes before it reaches systemic circulation** after oral administration. - While relevant to the oral bioavailability of these drugs, it does not describe the specific mechanism of elimination at high doses. *First order kinetics* - In this mechanism, a **constant fraction or percentage of the drug is eliminated per unit of time**, meaning the rate of elimination is directly proportional to the drug concentration. - Most drugs follow first-order kinetics at therapeutic doses because metabolizing enzymes are not saturated. *Second order kinetics* - This is a **less common pharmacokinetic model** where the rate of elimination is proportional to the square of the drug concentration or involves two reactants. - It does not typically describe the common elimination patterns of most drugs, including alcohol, aspirin, and phenytoin.
Question 5: Which of the following factors influences the duration of action of a drug?
- A. Bioavailability
- B. Clearance
- C. Rate of elimination
- D. All of the options (Correct Answer)
Explanation: ***All of the options*** - **Clearance** and **rate of elimination** are the primary determinants of how long a drug stays in the body at therapeutic levels, thus directly influencing its duration of action. - **Bioavailability** affects the intensity and onset but can influence the perceived duration if subtherapeutic concentrations are achieved. - The interplay of these pharmacokinetic parameters ultimately determines the drug's therapeutic window and frequency of dosing. *Clearance* - **Clearance** is the rate at which the active drug is removed from the body, primarily by the kidneys and liver. - A higher clearance generally leads to a shorter elimination half-life and a **shorter duration of action**, as the drug is removed more quickly from the systemic circulation. *Rate of elimination* - The **rate of elimination** directly dictates how quickly the concentration of a drug in the body decreases over time. - A faster elimination rate (shorter half-life) means the drug's effects will wear off sooner, resulting in a **shorter duration of action**. - This is quantified by the elimination rate constant (Kel) and half-life (t½). *Bioavailability* - **Bioavailability** refers to the fraction of an administered dose of unchanged drug that reaches the systemic circulation. - While bioavailability primarily affects the **peak concentration (Cmax)** and **intensity** of drug effect, it can indirectly influence duration. - If bioavailability is very low, therapeutic concentrations may not be sustained long enough, effectively shortening the **clinically relevant duration of action**. - However, two drugs with identical elimination rates but different bioavailabilities will have the same elimination half-life and similar duration at therapeutic doses.
Question 6: Which route of administration undergoes the maximum first pass metabolism?
- A. Intra-arterial
- B. Rectal
- C. Oral (Correct Answer)
- D. Intravenous
Explanation: ***Oral*** - Drugs administered orally are absorbed from the **gastrointestinal tract** and transported via the **portal vein** directly to the liver, where they undergo significant **first-pass metabolism** before reaching systemic circulation. - This hepatic metabolism can drastically reduce the **bioavailability** of the drug, requiring higher doses or alternative administration routes. *Intra-arterial* - This route delivers drugs directly into an **artery** supplying a target tissue or organ, largely bypassing systemic circulation and initial hepatic metabolism. - It is used for localized effects, such as **chemotherapy** for specific tumors, minimizing systemic exposure. *Rectal* - While a portion of rectally administered drugs may bypass the portal circulation by entering the **inferior and middle rectal veins**, a significant amount can still be absorbed into the superior rectal vein, which drains into the portal system. - This means rectal administration offers only **partial avoidance** of first-pass metabolism, making it less complete than IV or intra-arterial routes for bypassing the liver altogether. *Intravenous* - Drugs administered intravenously are delivered directly into the **systemic circulation**, completely bypassing the gastrointestinal tract and the liver's first-pass metabolism. - This route ensures **100% bioavailability** and rapid onset of action, as the drug immediately reaches its target.
Question 7: Which of the following drugs is known to have low first pass metabolism?
- A. Lidocaine
- B. Propranolol
- C. Theophylline (Correct Answer)
- D. Morphine
Explanation: ***Theophylline*** - **Theophylline** exhibits **low first-pass metabolism**, meaning a significant portion of the orally administered drug reaches systemic circulation unchanged. - This characteristic contributes to its relatively **high bioavailability** when given orally. *Lidocaine* - **Lidocaine** undergoes extensive **first-pass metabolism** in the liver, leading to very low oral bioavailability. - Due to this, it is typically administered **parenterally** (e.g., intravenously or topically) to achieve therapeutic concentrations. *Propranolol* - **Propranolol** is known for its significant **first-pass metabolism**, which results in a much lower bioavailability after oral administration compared to intravenous. - This extensive metabolism necessitates higher oral doses to achieve the same therapeutic effect as parenteral administration. *Morphine* - **Morphine** also undergoes substantial **first-pass metabolism** in the liver, where it is primarily glucuronidated. - This leads to a lower oral bioavailability compared to other routes of administration and contributes to a higher oral dose requirement.
Question 8: Which drug has the highest plasma protein binding?
- A. Warfarin (Correct Answer)
- B. Verapamil
- C. Aspirin
- D. GTN
Explanation: ***Warfarin*** - **Warfarin** exhibits very **high plasma protein binding**, typically greater than 99%, primarily to albumin. - This high binding capacity means that only a small fraction of the drug is free and pharmacologically active. - Due to high protein binding, warfarin is susceptible to drug interactions when displaced from albumin. *Verapamil* - **Verapamil** has a relatively high plasma protein binding, around 90%, but it is not as high as warfarin. - Its binding is predominantly to **albumin** and alpha-1-acid glycoprotein. *Aspirin* - **Aspirin** (acetylsalicylic acid) has moderate plasma protein binding, usually between 50-90%, depending on the dosage. - It binds to **albumin** and can displace other protein-bound drugs. *GTN* - **Glyceryl trinitrate (GTN)** has moderate plasma protein binding, approximately 60%. - Its rapid onset and short duration of action are primarily due to its extensive first-pass metabolism and quick redistribution, rather than protein binding characteristics.
Question 9: In the context of pharmacology, which plasma protein do acidic drugs primarily bind to?
- A. Globulin
- B. Albumin (Correct Answer)
- C. α1-acid glycoprotein
- D. None of the options
Explanation: ***Albumin*** - **Albumin** is the most abundant plasma protein and has multiple binding sites for a wide range of drugs, particularly **acidic drugs**. - Its high concentration and diverse binding capabilities make it the primary transporter for many **lipophilic** and **anionic drugs**. *Globulin* - **Globulins** are a diverse group of proteins, some of which bind to drugs, but they primarily transport **hormones**, **metals**, and **vitamins**, not acidic drugs. - They are less significant for binding acidic drugs compared to albumin. *α1-acid glycoprotein* - **α1-acid glycoprotein** primarily binds to **basic drugs** due to its numerous acidic residues. - While it plays a crucial role in binding basic compounds, it has limited affinity for acidic drugs. *None of the options* - This option is incorrect because **albumin** is a well-established and significant plasma protein for binding acidic drugs. - Specific plasma proteins are known to bind different types of drugs, and for acidic drugs, albumin is the primary binder.
Question 10: Microvesicular fatty liver is caused by ?
- A. Valproate (Correct Answer)
- B. Chronic diabetes mellitus (DM)
- C. Prolonged starvation
- D. Chronic inflammatory bowel disease (IBD)
Explanation: ***Valproate*** - **Valproate** is a known cause of **microvesicular steatosis**, particularly in children, due to its interference with mitochondrial fatty acid oxidation. - This can lead to severe liver injury, including **acute liver failure**, as it impairs the liver's ability to metabolize fats. *Chronic diabetes mellitus (DM)* - Chronic DM is commonly associated with **macrovesicular steatosis** (NAFLD), not microvesicular, due to insulin resistance and increased hepatic lipid synthesis. - Unlike microvesicular steatosis, macrovesicular type usually does not immediately impair mitochondrial function. *Prolonged starvation* - Prolonged starvation can lead to **fatty liver**, usually **macrovesicular steatosis**, as the body mobilizes fatty acids from adipose tissue. - While it stresses the liver, it rarely causes the specific **microvesicular** pattern of fat accumulation. *Chronic inflammatory bowel disease (IBD)* - IBD can cause various liver complications, but **microvesicular fatty liver** is not a characteristic feature. - Liver issues in IBD are more often related to **sclerosing cholangitis** or secondary to nutritional deficiencies and medications.