General Pharmacology — MCQs

General Pharmacology Indian Medical PG Practice Questions and MCQs

Question 101: Which of the following drugs can be given safely in pregnancy?

A. Amoxicillin (Correct Answer)
B. Methotrexate
C. Warfarin
D. Tetracycline

Explanation: **Explanation:** The safety of drugs during pregnancy is categorized based on their potential risk to the fetus. The correct answer is **Amoxicillin** because it belongs to the Penicillin group, which is classified as **FDA Category B**. These drugs have shown no evidence of fetal risk in animal studies and are considered the first-line, safest choice for treating bacterial infections in pregnant women. **Analysis of Incorrect Options:** * **Methotrexate (Option B):** A potent folic acid antagonist and **Category X** drug. It is highly teratogenic, causing "Methotrexate-aminopterin syndrome" (craniofacial anomalies, limb defects, and growth retardation). It is also used as an abortifacient. * **Warfarin (Option C):** A **Category X** anticoagulant. It crosses the placenta and causes **Fetal Warfarin Syndrome**, characterized by nasal hypoplasia, stippled epiphyses (chondrodysplasia punctata), and CNS defects. *Note: Heparin is the preferred anticoagulant in pregnancy as it does not cross the placenta.* * **Tetracycline (Option D):** A **Category D** drug. It chelates calcium and deposits in developing bones and teeth, leading to permanent **yellow-brown discoloration of teeth** and enamel hypoplasia in the child. **High-Yield NEET-PG Pearls:** * **Safe Antibiotics:** Penicillins, Cephalosporins, and Erythromycin (except the Estolate form, which causes hepatotoxicity in the mother). * **Teratogenic "Must-Knows":** * **Thalidomide:** Phocomelia (seal-like limbs). * **Valproate:** Neural tube defects (Spina bifida). * **ACE Inhibitors:** Renal dysgenesis and oligohydramnios. * **Phenytoin:** Fetal Hydantoin Syndrome (cleft lip/palate, digital hypoplasia).

Question 102: Constipation is caused by all of the following drugs EXCEPT:

A. Neostigmine (Correct Answer)
B. Atropine
C. Morphine
D. Fentanyl

Explanation: **Explanation:** The correct answer is **Neostigmine**. To answer this question, one must understand the effects of the Autonomic Nervous System and Opioids on gastrointestinal (GI) motility. **1. Why Neostigmine is the correct answer:** Neostigmine is an **acetylcholinesterase inhibitor**. By preventing the breakdown of acetylcholine, it increases cholinergic activity at muscarinic receptors in the gut. Acetylcholine is the primary excitatory neurotransmitter of the GI tract; its increase leads to **increased intestinal motility and peristalsis**. Therefore, Neostigmine is used clinically to treat paralytic ileus and pseudo-obstruction (Ogilvie’s syndrome), rather than causing constipation. It may actually cause diarrhea as a side effect. **2. Why the other options are incorrect:** * **Atropine:** This is a muscarinic antagonist (anticholinergic). It blocks the action of acetylcholine on the gut, leading to decreased motility and secretions, which results in **constipation**. * **Morphine & Fentanyl:** These are opioids. Opioids cause significant constipation (Opioid-Induced Constipation) by acting on **$\mu$-opioid receptors** in the myenteric plexus. This results in decreased intestinal propulsive contractions, increased sphincter tone, and increased water absorption from the stool. **High-Yield Clinical Pearls for NEET-PG:** * **Drug of choice for Post-operative paralytic ileus:** Neostigmine. * **Opioid-induced constipation:** Unlike respiratory depression or euphoria, patients **do not develop tolerance** to the constipating effects of opioids. * **Specific treatment for Opioid-induced constipation:** Methylnaltrexone or Naloxegol (peripherally acting $\mu$-opioid receptor antagonists). * **Anticholinergic Toxidrome Mnemonic:** "Dry as a bone" (decreased secretions/constipation), "Blind as a bat" (mydriasis), "Mad as a hatter" (delirium).

Question 103: Regarding drug conversion, which of the following is considered useless?

A. Inactive drug to inactive metabolite (Correct Answer)
B. Active drug to active metabolite
C. Inactive drug to active metabolite
D. All of the above

Explanation: **Explanation:** Drug metabolism (biotransformation) is the chemical alteration of a drug within the body, primarily aimed at making the compound more water-soluble for excretion. The clinical utility of these conversions varies: **1. Why Option A is Correct (Inactive drug to inactive metabolite):** This process is considered **pharmacologically useless** because it serves no therapeutic or physiological purpose. If a substance starts as inactive (exerting no effect) and ends as inactive, it neither treats the condition nor contributes to the drug's efficacy or toxicity. It is essentially a "null" pathway in clinical therapeutics. **2. Why the other options are wrong:** * **Active drug to active metabolite (Option B):** This is clinically significant as it prolongs the duration of drug action. For example, **Diazepam** is converted to **Desmethyldiazepam** (both are active), leading to a long-lasting sedative effect. * **Inactive drug to active metabolite (Option C):** This is the definition of a **Prodrug**. This is a highly useful strategy to improve oral bioavailability, reduce toxicity, or ensure site-specific delivery. For example, **Enalapril** (inactive) is converted to **Enalaprilat** (active) to inhibit ACE. **High-Yield Clinical Pearls for NEET-PG:** * **Prodrug Examples:** Levodopa (to Dopamine), Prednisone (to Prednisolone), Cyclophosphamide (to Phosphoramide mustard), and Clopidogrel. * **Active to Active Examples:** Codeine (to Morphine), Amitriptyline (to Nortriptyline), and Primidone (to Phenobarbitone). * **Exceptions:** Most drugs are converted from **Active to Inactive** (e.g., Paracetamol, Phenytoin). * **Lethal Synthesis:** A unique case where an inactive substance is converted into a **toxic** metabolite (e.g., Methanol to Formaldehyde).

Question 104: ED50 is a measure of:

A. Toxicity
B. Safety
C. Potency (Correct Answer)
D. Efficacy

Explanation: **Explanation:** **Why Potency is Correct:** **Potency** refers to the amount or concentration of a drug required to produce a specific intensity of effect. It is measured by the **ED50 (Median Effective Dose)**, which is the dose required to produce a specified therapeutic response in 50% of the population. On a Dose-Response Curve (DRC), potency is represented by the position of the curve along the X-axis (dose). A drug that achieves ED50 at a lower dose is considered more potent. **Why Other Options are Incorrect:** * **Toxicity:** This is measured by the **TD50** (Median Toxic Dose) or **LD50** (Median Lethal Dose). While ED50 relates to the therapeutic effect, TD50 relates to adverse or lethal effects. * **Safety:** The safety of a drug is determined by the **Therapeutic Index (TI)**, calculated as the ratio of **LD50/ED50**. A higher TI indicates a wider margin of safety. * **Efficacy:** This refers to the maximum effect (Emax) a drug can produce, regardless of dose. On a DRC, efficacy is represented by the height (Y-axis) of the curve. A drug can be highly potent but have low efficacy, or vice versa. **High-Yield Clinical Pearls for NEET-PG:** * **Potency vs. Efficacy:** Efficacy is clinically more important than potency. For example, Furosemide is more efficacious than Chlorothiazide because it can remove more fluid, even if Chlorothiazide requires a smaller dose (higher potency) to start its effect. * **Therapeutic Window:** The range between the minimum effective dose and the maximum tolerated dose. * **Standard Safety Margin:** Calculated as `[(LD1 - ED99) / ED99] × 100`. This is a more rigorous measure of safety than the Therapeutic Index.

Question 105: What are the effects of histamine?

A. Vasodilation
B. Bronchoconstriction
C. Increased vascular permeability
D. All of the above (Correct Answer)

Explanation: Histamine is a primary mediator of inflammation and allergic reactions, acting predominantly through **H1 and H2 receptors**. The correct answer is **"All of the above"** because histamine exerts systemic effects on the vascular and respiratory systems. ### **Mechanism of Action:** 1. **Vasodilation (Option A):** Histamine causes the relaxation of vascular smooth muscle, primarily via **H1 receptors** (through nitric oxide release) and **H2 receptors** (via cAMP). This leads to a decrease in total peripheral resistance and a fall in blood pressure. 2. **Bronchoconstriction (Option B):** In the lungs, histamine acts on **H1 receptors** located on bronchial smooth muscle, causing them to contract. This is a hallmark of allergic asthma and anaphylaxis. 3. **Increased Vascular Permeability (Option C):** Histamine causes the contraction of endothelial cells in post-capillary venules (via **H1 receptors**), creating gaps that allow fluid and proteins to leak into the extravascular space. This results in **edema** and is responsible for the "wheal" in the triple response. ### **Why other options are incorrect:** Options A, B, and C are all physiological hallmarks of histamine release. Therefore, selecting any single option would be incomplete. ### **High-Yield Clinical Pearls for NEET-PG:** * **Triple Response of Lewis:** Consists of **Red spot** (local vasodilation), **Flare** (axonal reflex vasodilation), and **Wheal** (exudation of fluid/edema). * **Gastric Acid Secretion:** Histamine acts on **H2 receptors** on parietal cells to increase HCl secretion (Target for H2 blockers like Ranitidine). * **Lewis Triple Response vs. Anaphylaxis:** While local histamine causes the triple response, systemic release leads to life-threatening anaphylactic shock (hypotension + bronchospasm). * **Drug of Choice:** For anaphylactic shock, the physiological antagonist is **Adrenaline** (not antihistamines).

Question 106: All of the following drugs can cross the placenta EXCEPT:

A. Phenytoin
B. Diazepam
C. Morphine
D. Heparin (Correct Answer)

Explanation: **Explanation:** The transfer of drugs across the placenta is primarily governed by **Fick’s Law of Diffusion**. For a drug to cross the placental barrier, it typically needs to be lipid-soluble, non-ionized, and have a low molecular weight (usually <500–600 Daltons). **Why Heparin is the Correct Answer:** **Heparin** is a large, highly polar (negatively charged) polysaccharide molecule with a high molecular weight (approx. 15,000 Daltons). Due to its **large size and high ionization**, it cannot cross the placental barrier. Consequently, heparin (and its derivative, LMWH) is the anticoagulant of choice during pregnancy as it poses no teratogenic risk to the fetus. **Why the Other Options are Incorrect:** * **Phenytoin:** An antiepileptic that is lipid-soluble and easily crosses the placenta. It is associated with **Fetal Hydantoin Syndrome**. * **Diazepam:** A benzodiazepine that is highly lipid-soluble. It crosses the placenta rapidly and can lead to "Floppy Infant Syndrome" if given near term. * **Morphine:** An opioid analgesic that is relatively small and lipid-soluble. It crosses the placenta and can cause neonatal respiratory depression or withdrawal symptoms (NAS). **NEET-PG High-Yield Pearls:** * **Warfarin vs. Heparin:** Unlike Heparin, **Warfarin** has a low molecular weight and crosses the placenta, making it highly teratogenic (causing Fetal Warfarin Syndrome/Chondrodysplasia punctata). * **Rule of Thumb:** "Large, charged molecules stay put." Insulin and Heparin are classic examples of drugs that do **not** cross the placenta. * **Crucial Exception:** Most antibodies (IgG) are large but cross the placenta via active transport, not passive diffusion.

Question 107: At what dose does intolerance to a drug typically occur in an individual?

A. Subtherapeutic dose
B. Therapeutic dose (Correct Answer)
C. Toxic dose
D. Not related to the dose of the drug

Explanation: **Explanation:** **Drug Intolerance** is defined as a qualitative exaggeration of the known pharmacodynamic effects of a drug occurring at **therapeutic doses**. It represents a low threshold of the individual to the action of the drug [1]. 1. **Why Option B is Correct:** Intolerance occurs when a patient experiences the expected pharmacological effect of a drug, but at an intensity that is normally seen only at much higher doses [1]. For example, a single tablet of Chloroquine causing severe vomiting or a small dose of Trinitroglycerin causing a throbbing headache. The key characteristic is that the drug is administered within the standard **therapeutic range**, but the individual’s biological response is hypersensitive [1]. 2. **Why Other Options are Incorrect:** * **Subtherapeutic dose (A):** While some idiosyncratic reactions can occur at very low doses, "intolerance" specifically refers to the inability to tolerate the standard clinical dose. * **Toxic dose (C):** Effects at toxic doses are classified as **Toxicity**. Toxicity is a predictable extension of the drug's action due to overdosage, whereas intolerance is an individual's unique sensitivity to a normal dose [2]. * **Not related to dose (D):** This describes **Drug Allergy** (Hypersensitivity). Allergic reactions are mediated by immunological mechanisms and are independent of the drug's pharmacological dose or action. **High-Yield Clinical Pearls for NEET-PG:** * **Intolerance vs. Idiosyncrasy:** Intolerance is a *quantitative* increase in the known effect, while Idiosyncrasy is a *qualitative* abnormal reaction due to genetic factors (e.g., Primaquine-induced hemolysis in G6PD deficiency). * **Tachyphylaxis:** Rapid development of tolerance after repeated doses in quick succession (e.g., Ephedrine, Tyramine). * **Drug Resistance:** Refers to the loss of effectiveness specifically in microorganisms or cancer cells.

Question 108: Which of the following is an anticholinergic side effect?

A. Salivation
B. Dryness (Correct Answer)
C. Gastrointestinal motility
D. Sweating

Explanation: **Explanation:** The correct answer is **Dryness**. Anticholinergic drugs (muscarinic antagonists like Atropine) work by competitively blocking the action of acetylcholine at muscarinic receptors. Since the parasympathetic nervous system is responsible for "rest and digest" functions—including the stimulation of exocrine glands—blocking these receptors leads to a significant reduction in secretions. This manifests clinically as dryness of the mouth (xerostomia), dry skin, and decreased bronchial secretions. **Analysis of Options:** * **Salivation:** This is a **cholinergic** effect mediated by M3 receptors. Anticholinergics cause the opposite (dry mouth). * **Gastrointestinal (GI) Motility:** Parasympathetic stimulation increases GI tone and peristalsis. Anticholinergics **decrease** motility, leading to constipation. * **Sweating:** While sweat glands are innervated by sympathetic fibers, they are unique because they use **acetylcholine** as the neurotransmitter (muscarinic receptors). Therefore, anticholinergics inhibit sweating (anhidrosis), leading to dry skin and potential hyperthermia. **High-Yield NEET-PG Pearls:** To remember the classic anticholinergic/Atropine overdose profile, use the mnemonic: * **Red as a beet:** Flushing (cutaneous vasodilation). * **Dry as a bone:** Anhidrosis and xerostomia. * **Blind as a bat:** Mydriasis and cycloplegia (loss of accommodation). * **Mad as a hatter:** Delirium and hallucinations. * **Hot as a hare:** Hyperthermia (due to lack of sweating). **Clinical Note:** Anticholinergics are contraindicated in patients with **Glaucoma** (can precipitate acute angle closure) and **Benign Prostatic Hyperplasia (BPH)** (can cause acute urinary retention).

Question 109: What does the ratio of LD50/ED50 represent?

A. Therapeutic index (Correct Answer)
B. Bioavailability
C. Potency
D. Efficacy

Explanation: ### Explanation **Therapeutic Index (TI)** is a quantitative measurement of the relative safety of a drug. It is calculated as the ratio of the **Median Lethal Dose (LD50)**—the dose that kills 50% of the test population—to the **Median Effective Dose (ED50)**—the dose that produces the desired therapeutic effect in 50% of the population. * **Formula:** $TI = LD50 / ED50$ * A higher TI indicates a wider margin of safety, meaning a much larger dose is required to cause toxicity than to produce a cure. **Analysis of Incorrect Options:** * **B. Bioavailability:** This refers to the fraction of an administered drug that reaches the systemic circulation in an unchanged form. It is determined by comparing plasma concentration-time curves (AUC) of oral vs. IV administration. * **C. Potency:** This refers to the amount of drug (dose) required to produce an effect of a given intensity. It is represented by the position of the Dose-Response Curve (DRC) on the x-axis (leftward shift = higher potency). * **D. Efficacy:** This is the maximum response ($E_{max}$) achievable by a drug, regardless of dose. It is represented by the height of the DRC on the y-axis. **High-Yield NEET-PG Pearls:** 1. **Certain Safety Factor:** Since LD50/ED50 only looks at the median, a more clinically relevant ratio is $LD1 / ED99$ (the ratio of the dose that kills 1% to the dose that is effective in 99%). 2. **Narrow Therapeutic Index Drugs:** These require **Therapeutic Drug Monitoring (TDM)** because their therapeutic and toxic doses are very close. * *Mnemonic:* **W**arfarin, **A**ntiepileptics (Phenytoin), **D**igoxin, **L**ithium, **T**heophylline (**W**ith **A** **D**igital **L**i**T**). 3. For human clinical use, **TD50** (Median Toxic Dose) is often used instead of LD50.

Question 110: What is the mechanism of action of Nitric oxide?

A. cGMP (Correct Answer)
B. cAMP
C. Ca++
D. Tyrosine

Explanation: **Mechanism of Action of Nitric Oxide (NO)** **Explanation of the Correct Answer (A):** Nitric Oxide (NO) is a potent endogenous vasodilator and a gaseous signaling molecule. It acts via the **cGMP (cyclic Guanosine Monophosphate) pathway**. 1. NO is released from vascular endothelial cells and diffuses into adjacent smooth muscle cells. 2. It activates the enzyme **soluble Guanylyl Cyclase (sGC)**. 3. This enzyme converts GTP into **cGMP**. 4. Increased cGMP activates Protein Kinase G (PKG), leading to dephosphorylation of myosin light chains and sequestration of intracellular calcium, resulting in **smooth muscle relaxation (vasodilation)**. **Why Other Options are Incorrect:** * **B. cAMP:** This is the second messenger for drugs like Beta-agonists (e.g., Salbutamol) and Prostacyclin ($PGI_2$). While it also causes vasodilation, it is not the primary pathway for NO. * **C. Ca++:** Nitric oxide actually works by *decreasing* intracellular calcium levels to cause relaxation. Increased calcium is typically associated with muscle contraction. * **D. Tyrosine:** This refers to Tyrosine Kinase receptors, which are utilized by insulin and various growth factors, not by gaseous signaling molecules like NO. **High-Yield Clinical Pearls for NEET-PG:** * **Nitrates (Nitroglycerin):** Act as prodrugs that are metabolized to release NO, utilizing this same cGMP pathway to relieve angina. * **PDE-5 Inhibitors (Sildenafil):** These drugs inhibit the breakdown of cGMP. Since NO increases cGMP, Sildenafil potentiates NO-mediated vasodilation (used in Erectile Dysfunction and Pulmonary Hypertension). * **Inhaled NO:** Used clinically in the management of Persistent Pulmonary Hypertension of the Newborn (PPHN). * **EDRF:** Nitric Oxide was formerly known as Endothelium-Derived Relaxing Factor.

Practice by Chapter

Pharmacokinetics: Absorption and Distribution

Practice Questions

Pharmacokinetics: Metabolism and Excretion

Practice Questions

Pharmacodynamics and Receptor Theory

Practice Questions

Drug-Receptor Interactions and Dose-Response

Practice Questions

Pharmacogenetics and Personalized Medicine

Practice Questions

Adverse Drug Reactions and Toxicity

Practice Questions

Drug Interactions

Practice Questions

Drug Development and Regulation

Practice Questions

Pediatric and Geriatric Pharmacology

Practice Questions

Placental Transfer and Lactation

Practice Questions

Want unlimited practice?

Get full access to all questions, explanations, and performance tracking.

Start For Free