High volume of distribution is primarily determined by:
Which of the following drugs is NOT metabolized by acetylation?
Which of the following statements represents the most clinically significant aspect of drug metabolism?
Which of the following is an example of topical administration producing only local effects (not systemic)?
Which of the following pairs are considered physiological antagonists in pharmacology?
Which of the following drug combinations demonstrates receptor level antagonism?
Which of the following is not a common side effect of clonidine?
Which of the following is a lipid insoluble beta-blocker?
Which non-selective beta-blocker has sympathomimetic activity?
Which of the following is non-selective 3rd generation Beta blocker ?
NEET-PG 2015 - Pharmacology NEET-PG Practice Questions and MCQs
Question 41: High volume of distribution is primarily determined by:
- A. High lipid solubility (Correct Answer)
- B. High plasma protein binding
- C. Elimination rate
- D. Half-life of the drug
Explanation: ***High lipid solubility***- Highly **lipid-soluble** drugs readily cross biological membranes and distribute extensively into tissues, including adipose tissue, CNS, and intracellular compartments, leading to a **high volume of distribution (Vd)** [1, 2].- This property allows the drug to move out of the bloodstream and into various body compartments, increasing the apparent volume in which the drug is dissolved [1].*High plasma protein binding*- **High plasma protein binding** generally **restricts** drug distribution to tissues because only the **unbound (free) fraction** can diffuse across capillary membranes into interstitial fluid and cells [1].- This typically leads to a **lower Vd**, as the drug is largely retained within the plasma compartment.*Elimination rate*- The **elimination rate** determines how quickly the drug is removed from the body, affecting the **duration of action** rather than the extent of distribution.- It influences drug concentration changes over time but does not directly determine the physical space (volume) into which the drug distributes.*Half-life of the drug*- The **half-life (t½)** is the time required for drug concentration to reduce by half, and it is **determined by** both Vd and clearance (t½ = 0.693 × Vd/CL).- Half-life is a **consequence** of Vd and clearance, not a primary determinant of how widely a drug distributes [3].
Question 42: Which of the following drugs is NOT metabolized by acetylation?
- A. Dapsone
- B. Metoclopramide (Correct Answer)
- C. Procainamide
- D. INH
Explanation: ***Metoclopramide*** - **Metoclopramide** is eliminated primarily via renal excretion, with a smaller portion undergoing glucuronidation and sulfation, not acetylation. - Its metabolic pathway does not involve the enzyme **N-acetyltransferase**, which is responsible for acetylation. *Dapsone* - **Dapsone** undergoes significant **N-acetylation** by NAT2 (N-acetyltransferase 2), which is important for its metabolism and clearance. - Genetic variations in NAT2 can lead to individual differences in **dapsone acetylation rates**, affecting drug efficacy and toxicity. *Procainamide* - **Procainamide** is primarily metabolized by N-acetyltransferase 2 (NAT2) to **N-acetylprocainamide (NAPA)**, an active metabolite. - Differences in **acetylation phenotype** (slow vs. rapid acetylators) influence the metabolism of procainamide and the risk of drug-induced lupus. *INH* - **Isoniazid (INH)** is extensively metabolized in the liver, primarily by **N-acetylation** via the enzyme N-acetyltransferase 2 (NAT2). - The rate of INH acetylation varies significantly among individuals, classifying them as **slow or rapid acetylators**, which impacts drug toxicity and efficacy.
Question 43: Which of the following statements represents the most clinically significant aspect of drug metabolism?
- A. Most common enzyme involved is CYP 3A4/5 (Correct Answer)
- B. Glucuronidation is a phase II reaction
- C. Reduction is a phase I reaction
- D. Cytochrome P450 is involved in phase I reactions
Explanation: ***Most common enzyme involved is Cyp 3A4/5*** - CYP3A4/5 is the **most abundant and clinically significant** cytochrome P450 enzyme, responsible for metabolizing approximately **50% of all clinically used drugs**. - Its widespread involvement means variations in its activity (due to **genetics, drug interactions, or disease**) have a major impact on drug efficacy and toxicity. *Glucuronidation is a phase II reaction* - While correct that glucuronidation is a **Phase II metabolic reaction**, this statement describes a biochemical classification rather than a clinically significant aspect compared to the involvement of CYP3A4/5. - Phase II reactions generally involve **conjugation** to increase water solubility and facilitate excretion, but they do not collectively account for as many drug interactions as CYP3A4/5 alone. *Reduction is a phase I reaction* - This statement is factually correct as **reduction** is indeed a **Phase I metabolic reaction**. - However, it represents a generic classification of a metabolic pathway and doesn't highlight the specific clinical importance or prevalence of a particular enzyme or reaction in drug metabolism. *Cytochrome P450 is involved in phase I reactions* - This is true; the **cytochrome P450 system** is the primary enzyme system for **Phase I metabolism**, which introduces or exposes polar groups to make drugs more reactive. - While fundamentally important, this statement is too broad; it does not specify the most clinically significant *aspect* or *enzyme* within the P450 system compared to directly identifying CYP3A4/5.
Question 44: Which of the following is an example of topical administration producing only local effects (not systemic)?
- A. Topical corticosteroid cream (Correct Answer)
- B. Sublingual nitroglycerin
- C. Transdermal patch
- D. Rectal diazepam
Explanation: ***Topical corticosteroid cream*** - When applied to the skin for conditions like dermatitis, topical corticosteroids primarily exert their effects at the site of application, reducing **local inflammation** and itching. - While systemic absorption can occur with potent steroids over large areas, typical use aims for **localized action** without significant systemic effects. *Sublingual nitroglycerin* - This route is designed for **rapid systemic absorption** through the oral mucosa, bypassing first-pass metabolism to quickly treat angina. - The goal is a **widespread vasodilatory effect** throughout the body, not a local one within the mouth. *Transdermal patch* - Transdermal patches, such as those for nicotine or fentanyl, are specifically designed to deliver medication **systemically** through the skin into the bloodstream over a prolonged period. - They provide a **sustained release** and systemic therapeutic effect throughout the body. *Rectal diazepam* - Administered rectally, diazepam is absorbed into the systemic circulation to produce **CNS effects** such as sedation, anxiolysis, or anticonvulsant activity. - Although the administration is local, the intended clinical effect is **systemic** and widespread throughout the body.
Question 45: Which of the following pairs are considered physiological antagonists in pharmacology?
- A. Adrenaline and Isoprenaline
- B. Isoprenaline and Propranolol
- C. Histamine and Adrenaline (Correct Answer)
- D. All of the options
Explanation: ***Histamine and Adrenaline*** - **Physiological antagonism** occurs when two drugs produce opposite effects by acting on different receptors or pathways. - **Histamine** causes bronchoconstriction and vasodilation, while **adrenaline** causes bronchodilation and vasoconstriction, counteracting each other's effects through different mechanisms. *Adrenaline and Isoprenaline* - Both **adrenaline** and **isoprenaline** are **adrenergic agonists** that produce similar physiological effects, primarily through beta-adrenergic receptor activation. - They are not physiological antagonists but rather have **synergistic** or similar pharmacological actions. *Isoprenaline and Propranolol* - **Isoprenaline** is a **beta-adrenergic agonist**, while **propranolol** is a **beta-adrenergic antagonist**. - This is an example of **pharmacological antagonism (receptor antagonism)**, where one drug blocks the effect of another at the same receptor site, rather than physiological antagonism.
Question 46: Which of the following drug combinations demonstrates receptor level antagonism?
- A. Histamine and Adrenaline
- B. Isoprenaline (agonist) and Propranolol (antagonist) (Correct Answer)
- C. Adrenaline and Isoprenaline
- D. None of the options
Explanation: ***Isoprenaline (agonist) and Propranolol (antagonist)*** - **Propranolol** is a **beta-adrenergic receptor antagonist**, meaning it binds to and blocks beta-adrenergic receptors. - **Isoprenaline** is a **beta-adrenergic receptor agonist**, meaning it activates these same receptors. Their combined action demonstrates **receptor-level antagonism** as propranolol prevents isoprenaline from binding and eliciting its effect. *Histamine and Adrenaline* - This combination illustrates **physiological antagonism**, where two drugs produce opposite effects through different mechanisms and different receptors. - **Adrenaline** causes bronchodilation and vasoconstriction via adrenergic receptors, counteracting the effects of **histamine** (e.g., bronchoconstriction, vasodilation) which acts on histamine receptors. *Adrenaline and Isoprenaline* - Both **adrenaline** and **isoprenaline** are **agonists** of adrenergic receptors, specifically beta-adrenergic receptors. - They would produce similar effects (e.g., increased heart rate, bronchodilation) rather than opposing each other at the receptor level. *None of the options* - This is incorrect because **Isoprenaline and Propranolol** is a valid example of receptor-level antagonism, making this option unnecessary.
Question 47: Which of the following is not a common side effect of clonidine?
- A. Xerostomia
- B. Sedation
- C. Diarrhea (Correct Answer)
- D. Impotency
Explanation: ***Diarrhea*** - **Clonidine** commonly causes **constipation**, not diarrhea, due to its **alpha-2 adrenergic agonist** effects, which decrease gastrointestinal motility. - Diarrhea is not typically associated with clonidine's mechanism of action or adverse effect profile. *Xerostomia* - **Xerostomia** (dry mouth) is a very common side effect of **clonidine** occurring in up to 40% of patients. - This results from **alpha-2 agonist** activity that reduces sympathetic stimulation of salivary gland secretions. - This symptom can significantly impact patient compliance and quality of life. *Sedation* - **Sedation** is a frequent side effect of **clonidine**, particularly when initiating treatment or increasing dosage, because it acts as an **alpha-2 agonist** in the central nervous system, reducing sympathetic outflow and promoting drowsiness. - Patients are often advised to avoid driving or operating heavy machinery until they know how the medication affects them. *Impotency* - **Impotency** or **erectile dysfunction** is a recognized and common sexual side effect of **clonidine**, which can interfere with quality of life and adherence to treatment for hypertension. - This effect is related to the drug's impact on the autonomic nervous system and vascular tone through central alpha-2 agonism.
Question 48: Which of the following is a lipid insoluble beta-blocker?
- A. Timolol
- B. Carvedilol
- C. Pindolol
- D. Celiprolol (Correct Answer)
Explanation: ***Celiprolol*** - **Celiprolol** is a **hydrophilic** (lipid-insoluble) beta-blocker, meaning it has low lipid solubility and does not readily cross the blood-brain barrier. - This property reduces the likelihood of **CNS side effects** such as nightmares and insomnia. *Timolol* - **Timolol** is a **lipophilic** (lipid-soluble) beta-blocker, allowing it to penetrate the central nervous system. - Its high lipid solubility contributes to a higher incidence of **CNS side effects**. *Carvedilol* - **Carvedilol** is a **lipophilic** mixed alpha and beta-blocker, which means it can cross the blood-brain barrier. - This can lead to central nervous system effects, although its primary clinical use is in heart failure and hypertension. *Pindolol* - **Pindolol** is a **lipophilic** beta-blocker with intrinsic sympathomimetic activity (ISA). - Its lipid solubility allows it to enter the brain, potentially causing **CNS-related side effects**.
Question 49: Which non-selective beta-blocker has sympathomimetic activity?
- A. Nadolol
- B. Pindolol (Correct Answer)
- C. Acebutalol
- D. Metoprolol
Explanation: ***Pindolol*** - **Pindolol** is a **non-selective beta-blocker** that exhibits **intrinsic sympathomimetic activity (ISA)**, meaning it acts as a partial agonist at beta-adrenergic receptors. - Due to ISA, it causes less reduction in resting heart rate and cardiac output compared to beta-blockers without ISA. *Acebutalol* - **Acebutalol** is a **beta-1 selective blocker** (cardioselective) that possesses **intrinsic sympathomimetic activity (ISA)**. - While it has ISA, it is not a non-selective beta-blocker, making it an incorrect answer for this question. *Nadolol* - **Nadolol** is a **non-selective beta-blocker** that does **not** have intrinsic sympathomimetic activity (ISA). - It primarily acts as a pure antagonist at both beta-1 and beta-2 adrenergic receptors. *Metoprolol* - **Metoprolol** is a **beta-1 selective blocker** (cardioselective) and does **not** possess intrinsic sympathomimetic activity (ISA). - Its primary action is blockade of cardiac beta-1 receptors.
Question 50: Which of the following is non-selective 3rd generation Beta blocker ?
- A. Betaxolol
- B. Celiprolol
- C. Nebivolol
- D. Carvedilol (Correct Answer)
Explanation: ***Carvedilol*** - **Carvedilol** is a **non-selective beta-adrenergic antagonist** (blocks both β1 and β2 receptors) with **additional α1-adrenergic blocking activity**, making it a true **3rd generation beta-blocker**. - The α1-blockade provides **vasodilatory properties**, reducing peripheral vascular resistance and improving hemodynamics. - It has favorable effects on lipid metabolism and insulin sensitivity, making it particularly useful in heart failure and hypertension. - Its non-selective beta-blockade combined with vasodilation distinguishes it from selective 3rd generation agents. *Betaxolol* - **Betaxolol** is a **selective β1-adrenergic antagonist** without vasodilatory properties. - Classified as a **2nd generation beta-blocker** due to its cardioselectivity. - Primarily used in glaucoma and hypertension but lacks the non-selective profile and additional mechanisms of 3rd generation agents. *Celiprolol* - **Celiprolol** is a **β1-selective antagonist** with **β2-agonistic effects** providing vasodilation. - While classified as 3rd generation due to vasodilatory properties, it is **selective for β1**, not non-selective. - Its β2-agonism causes peripheral vasodilation but maintains β1-selectivity. *Nebivolol* - **Nebivolol** is a highly **selective β1-adrenergic antagonist** with **vasodilatory effects via nitric oxide (NO) release**. - Classified as 3rd generation due to NO-mediated vasodilation, but it is **β1-selective**, not non-selective. - The combination of high β1-selectivity and endothelial-mediated vasodilation makes it unique among 3rd generation agents.