General Pharmacology — MCQs

General Pharmacology Indian Medical PG Practice Questions and MCQs

Question 11: The conversion of an optically pure isomer (enantiomer) into a mixture of equal amounts of both dextro and levo forms is called as?

A. Polymerization
B. Stereoisomerization
C. Racemization (Correct Answer)
D. Fractionation

Explanation: ### Explanation **Correct Option: C. Racemization** Racemization is the chemical process by which an optically active substance (a pure enantiomer) is converted into an optically inactive mixture containing equal amounts of both dextrorotatory (+) and levorotatory (–) forms. This mixture is known as a **racemic mixture**. Because the two enantiomers rotate plane-polarized light in opposite directions by equal amounts, the net optical rotation of a racemic mixture is zero. **Why other options are incorrect:** * **A. Polymerization:** This is a process where small molecules (monomers) combine chemically to produce a very large chain-like or network molecule (polymer). It is unrelated to optical activity. * **B. Stereoisomerization:** This is a broad umbrella term for the interconversion of any stereoisomers (including diastereomers or geometric isomers). While racemization is a *type* of stereoisomerization, "Racemization" is the specific and most accurate term for creating a 50:50 mixture of enantiomers. * **D. Fractionation:** This is a separation process (like fractional distillation) used to divide a mixture into its individual components or "fractions" based on physical properties like boiling points. **High-Yield Clinical Pearls for NEET-PG:** * **Thalidomide Tragedy:** A classic example of enantiomer differences. The (R)-enantiomer is a sedative, while the (S)-enantiomer is a potent teratogen causing phocomelia. In the body, these enantiomers can undergo **spontaneous in-vivo racemization**, which is why giving only the "safe" isomer did not prevent toxicity. * **Esmomeprazole vs. Omeprazole:** Omeprazole is a racemic mixture, whereas Esomeprazole is the pure (S)-enantiomer, which offers better bioavailability and more consistent acid suppression. * **Levocetirizine:** The (R)-enantiomer of Cetirizine; it has a higher affinity for H1 receptors and fewer side effects than the racemic mixture.

Question 12: Phase I clinical trials are primarily conducted to assess what aspect of a new drug?

A. Safety and tolerability
B. Therapeutic efficacy
C. Optimal dosage range
D. Pharmacokinetic profile (Correct Answer)

Explanation: **Explanation:** **Correct Answer: D. Pharmacokinetic profile** Phase I clinical trials represent the first stage of testing a new investigational drug in humans. The primary objective is to establish the **pharmacokinetic (PK) profile**, which includes absorption, distribution, metabolism, and excretion (ADME) parameters [1]. This phase determines how the human body handles the drug, helping researchers establish the initial safety margins and biological effects [3]. **Analysis of Options:** * **A. Safety and tolerability:** While Phase I does assess safety and identifies the Maximum Tolerated Dose (MTD), the fundamental scientific goal in this initial human exposure is to map the PK profile [1], [3]. * **B. Therapeutic efficacy:** This is the primary objective of **Phase II** (Proof of Concept) and **Phase III** (Confirmatory) trials [1]. Phase I is typically conducted on healthy volunteers (except for toxic drugs like anti-cancer agents), where efficacy cannot be measured [1], [3]. * **C. Optimal dosage range:** Determining the definitive therapeutic dose range is the goal of **Phase II** clinical trials [1]. Phase I only identifies the dose-limiting toxicity. **High-Yield Clinical Pearls for NEET-PG:** * **Study Population:** Usually 20–80 **healthy volunteers** (Exception: Oncology drugs, where patients are used) [3]. * **Phase 0 (Microdosing):** Conducted before Phase I using sub-therapeutic doses to study PK properties and reduce the risk of toxicity. * **Phase IV:** Post-marketing surveillance to detect rare adverse effects (e.g., Phocomelia with Thalidomide) [2]. * **Success Rate:** Phase I has the highest success rate (~70%) compared to subsequent phases.

Question 13: Which of the following drugs is classified as FDA pregnancy category B, indicating that adequate studies in pregnant women have failed to demonstrate a risk to the fetus?

A. Ranitidine (Correct Answer)
B. Pilocarpine
C. Latanoprost
D. Dorzolamide

Explanation: **Explanation:** The classification of drugs during pregnancy is a high-yield topic for NEET-PG. The FDA Pregnancy Categories (A, B, C, D, and X) help clinicians assess fetal risk. **Correct Answer: A. Ranitidine** Ranitidine is an $H_2$ receptor antagonist used to treat GERD and peptic ulcers. It is classified as **Category B**. In Category B, animal reproduction studies have failed to demonstrate a risk to the fetus, and there are no adequate and well-controlled studies in pregnant women. Alternatively, if animal studies showed an adverse effect, adequate studies in pregnant women failed to demonstrate a risk during the first trimester. Ranitidine is considered safe for managing acid reflux during pregnancy when lifestyle modifications fail. **Analysis of Incorrect Options:** * **B. Pilocarpine (Category C):** A cholinergic agonist used in glaucoma. Animal studies have shown adverse effects (skeletal abnormalities), and there are no adequate human studies. It should only be used if the potential benefit justifies the potential risk. * **C. Latanoprost (Category C):** A prostaglandin analogue. It has shown embryocidal effects in animals at high doses. * **D. Dorzolamide (Category C):** A carbonic anhydrase inhibitor. Like most newer ophthalmic medications, it lacks sufficient human data and has shown teratogenic potential in animal models (e.g., malformations of the vertebral bodies). **High-Yield Clinical Pearls for NEET-PG:** * **Category A:** Safest (e.g., Folic acid, Pyridoxine). * **Category B:** Generally safe (e.g., Amoxicillin, Paracetamol, Ranitidine, Metformin). * **Category X:** Absolutely contraindicated (e.g., Thalidomide, Methotrexate, Statins, Warfarin). * **Note:** The FDA is currently phasing out these letter categories in favor of the **PLLR (Pregnancy and Lactation Labeling Rule)**, but letter categories remain frequently tested in Indian PG exams.

Question 14: If a drug is excreted in urine at the rate of 10 mg/hr at a steady-state plasma concentration of 5 mg/L, then its renal clearance is:

A. 0.5 L/hr
B. 2.0 L/hr (Correct Answer)
C. 5.0 L/hr
D. 20 L/hr

Explanation: ### Explanation **Concept and Calculation:** Renal clearance ($CL_r$) is defined as the volume of plasma that is completely cleared of a drug by the kidneys per unit of time. It is calculated using the formula: $$CL_r = \frac{\text{Rate of Elimination (Urine)}}{\text{Plasma Concentration (Cp)}}$$ In this question: * **Rate of elimination** = $10\text{ mg/hr}$ * **Steady-state plasma concentration ($C_{ss}$)** = $5\text{ mg/L}$ * **Calculation:** $CL_r = \frac{10\text{ mg/hr}}{5\text{ mg/L}} = \mathbf{2.0\text{ L/hr}}$ **Analysis of Options:** * **Option B (2.0 L/hr) is Correct:** This directly follows the standard clearance formula. * **Option A (0.5 L/hr):** This is an error resulting from dividing plasma concentration by the elimination rate ($5/10$), which is mathematically incorrect. * **Option C (5.0 L/hr):** This value does not correlate with the provided data; it may be a distractor using the plasma concentration value. * **Option D (20 L/hr):** This results from multiplying the two values ($10 \times 2$) instead of dividing them. **NEET-PG High-Yield Pearls:** 1. **Clearance vs. Elimination:** Clearance is a **volume** per unit time (L/hr), whereas the elimination rate is an **amount** per unit time (mg/hr). 2. **Comparison with GFR:** * If $CL_r < \text{GFR}$ ($125\text{ mL/min}$), the drug undergoes **tubular reabsorption**. * If $CL_r > \text{GFR}$, the drug undergoes **active tubular secretion**. 3. **Loading Dose:** Clearance determines the **Maintenance Dose**, while Volume of Distribution ($V_d$) determines the **Loading Dose**. 4. **First-order Kinetics:** For most drugs, clearance remains constant regardless of plasma concentration.

Question 15: Misoprostol is an analogue of which prostaglandin?

A. PGE1 (Correct Answer)
B. PGE2
C. PGF2alpha
D. PGI2

Explanation: **Explanation:** **Misoprostol** is a synthetic methyl analogue of **Prostaglandin E1 (PGE1)**. It is primarily used for its cytoprotective effects on the gastric mucosa and its potent oxytocic properties. 1. **Why PGE1 is correct:** Misoprostol mimics the action of endogenous PGE1. In the stomach, it binds to EP3 receptors on parietal cells to inhibit gastric acid secretion and stimulates mucus and bicarbonate secretion. In the uterus, it causes cervical ripening and uterine contractions. 2. **Why other options are incorrect:** * **PGE2 (Dinoprostone):** While also used for cervical ripening, Misoprostol is specifically a PGE1 analogue, not PGE2. * **PGF2alpha (Carboprost/Latanoprost):** These analogues are used to control postpartum hemorrhage (Carboprost) or treat glaucoma (Latanoprost/Bimatoprost), but they differ structurally and functionally from Misoprostol. * **PGI2 (Epoprostenol):** This is Prostacyclin, used primarily as a vasodilator in pulmonary arterial hypertension. **High-Yield Clinical Pearls for NEET-PG:** * **NSAID-induced Ulcers:** Misoprostol is the drug of choice for the *prevention* of NSAID-induced gastric ulcers (though PPIs are more commonly used in practice due to better tolerability). * **Obstetrics:** It is used for medical abortion (in combination with Mifepristone), induction of labor, and management of postpartum hemorrhage (PPH). * **Side Effects:** The most common side effect is **diarrhea** and abdominal cramps. * **Contraindication:** It is strictly contraindicated in pregnancy (Category X) unless used for legal termination, due to its potent abortifacient properties.

Question 16: Type A (augmented) adverse drug reactions are characterized by all EXCEPT:

A. Qualitatively abnormal responses to the drug (Correct Answer)
B. Predictable from the drug's known pharmacological or toxicological effects
C. Generally dose-dependent
D. Usually common

Explanation: Adverse drug reactions (ADRs) are primarily classified into two types: **Type A (Augmented)** and **Type B (Bizarre)**. ### Why Option A is the Correct Answer **Qualitatively abnormal responses** are the hallmark of **Type B (Bizarre)** reactions, not Type A. Type B reactions (like penicillin anaphylaxis or idiosyncratic reactions) are unrelated to the drug's known pharmacological action and occur only in susceptible individuals. In contrast, Type A reactions are **qualitatively normal but quantitatively increased** (e.g., excessive bleeding with warfarin) [2]. ### Explanation of Incorrect Options * **Option B (Predictable):** Type A reactions are predictable because they are based on the drug’s primary or secondary pharmacological properties [1]. For example, hypoglycemia is a predictable extension of the effect of insulin [3]. * **Option C (Dose-dependent):** These reactions are directly related to the dose administered. Reducing the dose usually resolves the reaction, which is a key management strategy for Type A ADRs [1], [3]. * **Option D (Common):** Type A reactions account for approximately 80% of all ADRs. Because they are predictable and dose-related, they occur frequently in clinical practice [2]. ### NEET-PG High-Yield Pearls * **Mnemonic for Type A:** **A**ugmented, **A**ccepted (predictable), **A**voidable (by dose adjustment). * **Mnemonic for Type B:** **B**izarre, **B**one-breaking (often severe), **B**elieve it or not (unpredictable). * **Type C (Continuous):** Due to long-term use (e.g., Analgesic nephropathy). * **Type D (Delayed):** Occurs years after treatment (e.g., Teratogenicity or Carcinogenicity). * **Type E (End of use):** Withdrawal symptoms (e.g., Clonidine rebound hypertension).

Question 17: Which of the following drugs is administered intranasally?

A. Desmopressin (Correct Answer)
B. Ribavarin
C. Amiloride
D. Oseltamivir

Explanation: **Explanation:** **Desmopressin (Correct Answer):** Desmopressin is a synthetic analogue of Vasopressin (ADH). It is commonly administered **intranasally** because it is a peptide drug that would otherwise be degraded by gastric enzymes if taken orally (though oral formulations exist with higher doses). The nasal route provides rapid absorption through the vascularized nasal mucosa, bypassing first-pass metabolism. It is the preferred route for treating **Central Diabetes Insipidus** and nocturnal enuresis. **Analysis of Incorrect Options:** * **Ribavirin:** This antiviral is primarily administered **orally** or via **aerosol inhalation** (using a small particle aerosol generator) specifically for treating Respiratory Syncytial Virus (RSV) in infants. * **Amiloride:** A potassium-sparing diuretic used in hypertension and heart failure, it is administered **orally**. (Note: While experimental inhaled versions exist for Cystic Fibrosis, it is not the standard clinical route). * **Oseltamivir:** This neuraminidase inhibitor used for Influenza is a prodrug administered **orally**. In contrast, Zanamivir (another neuraminidase inhibitor) is administered via inhalation. **High-Yield Clinical Pearls for NEET-PG:** * **Desmopressin (DDAVP)** acts on **V2 receptors** with minimal V1 (vasoconstrictor) activity, making it safer for patients with cardiovascular issues compared to natural ADH. * **Other drugs given intranasally:** Calcitonin (for osteoporosis), GnRH agonists (Buserelin), Midazolam (for acute seizures), and Sumatriptan (for migraines). * **Therapeutic uses of Desmopressin:** Central Diabetes Insipidus, Type 1 Von Willebrand Disease, and Hemophilia A (it increases Factor VIII and vWF levels).

Question 18: Phocomelia is due to the teratogenic effect of:

A. Thalidomide (Correct Answer)
B. Chlorpromazine
C. Methotrexate
D. Carbamazepine

Explanation: **Explanation:** **Phocomelia** is a rare congenital deformity characterized by the malformation of limbs, where the hands or feet are attached close to the trunk, resembling seal flippers. **1. Why Thalidomide is Correct:** Thalidomide was originally marketed in the 1950s as a sedative and anti-emetic for morning sickness. It is the classic example of a teratogen that causes **Phocomelia** (limb reduction defects). The mechanism involves the inhibition of **angiogenesis** and the degradation of transcription factors (like SALL4) via the cereblon E3 ubiquitin ligase complex during the critical period of limb bud development (3rd to 8th week of gestation). **2. Why Other Options are Incorrect:** * **Chlorpromazine:** An antipsychotic generally considered safe regarding structural malformations, though it may cause neonatal withdrawal symptoms if used near term. * **Methotrexate:** A folate antagonist that causes **Fetal Hydantoin-like syndrome** or "Methotrexate Embryopathy," characterized by cranial bone anomalies, cleft palate, and growth retardation, but not specifically phocomelia. * **Carbamazepine:** An antiepileptic associated with **Neural Tube Defects (NTDs)**, such as spina bifida, and craniofacial defects. **3. Clinical Pearls for NEET-PG:** * **Current Uses of Thalidomide:** Despite its history, it is now used for **Multiple Myeloma** and **Erythema Nodosum Leprosum (ENL)**. * **STEPS Program:** Due to its teratogenicity, it is prescribed under strict pregnancy prevention programs. * **Other limb defects:** Warfarin causes chondrodysplasia punctata (stippled epiphyses), while Valproate is most notorious for Spina Bifida.

Question 19: H1 antihistamines are beneficial in several conditions. Which of the following conditions is NOT benefited by the antagonism of histamine?

A. Dermographism
B. Insect bite
C. Common cold (Correct Answer)
D. Seasonal hay fever

Explanation: **Explanation:** The correct answer is **Common cold** because the symptoms of the common cold (rhinorrhea, sneezing, and congestion) are primarily caused by **viral inflammation** and the release of kinins and prostaglandins, rather than histamine. While first-generation H1 antihistamines (like diphenhydramine or chlorpheniramine) are often found in over-the-counter cold remedies, their benefit is derived from their **anticholinergic (atropine-like) side effects**, which help dry up nasal secretions, rather than their antihistaminic action. **Analysis of other options:** * **Dermographism:** This is a form of physical urticaria where pressure on the skin causes a wheal-and-flare response. This reaction is directly mediated by the release of histamine from mast cells, making H1 blockers highly effective. * **Insect bite:** The local redness, itching, and swelling following an insect bite are classic Type I hypersensitivity reactions mediated by histamine release. * **Seasonal hay fever (Allergic Rhinitis):** This is a prototypical IgE-mediated allergic reaction where histamine is the primary mediator of sneezing, itching, and watery eyes. H1 antihistamines are the first-line treatment. **High-Yield Clinical Pearls for NEET-PG:** * **Mechanism:** H1 antihistamines are technically **inverse agonists**, not simple competitive antagonists; they stabilize the inactive state of the H1 receptor. * **First vs. Second Gen:** First-generation H1 blockers (e.g., Promethazine) cross the blood-brain barrier and are sedative. Second-generation blockers (e.g., Cetirizine, Loratadine) are non-sedating. * **Terfenadine/Astemizole:** These second-generation drugs were withdrawn because they cause **QT prolongation** and *Torsades de Pointes* when taken with CYP3A4 inhibitors (like Ketoconazole or Erythromycin). Fexofenadine is their safe active metabolite.

Question 20: Adrenaline, noradrenaline, and dopamine act through which type of receptor?

A. Two pass receptor
B. Ligand-gated channel
C. Seven pass receptor (Correct Answer)
D. One pass receptor

Explanation: **Explanation:** The correct answer is **C. Seven pass receptor.** Adrenaline, noradrenaline, and dopamine are catecholamines that act as ligands for **G-Protein Coupled Receptors (GPCRs)**. These receptors are characterized by a single polypeptide chain that traverses the cell membrane **seven times**, which is why they are structurally referred to as **Seven-pass receptors** or **Serpentine receptors**. * **Adrenaline and Noradrenaline** act on adrenergic receptors ($\alpha$ and $\beta$). * **Dopamine** acts on dopaminergic receptors ($D_1$ through $D_5$). All of these are classic examples of GPCRs that utilize second messengers like cAMP or $IP_3/DAG$ to exert their cellular effects. **Why other options are incorrect:** * **A. Two-pass receptor:** This is not a standard classification for major neurotransmitter receptors. * **B. Ligand-gated channel:** Also known as ionotropic receptors (e.g., Nicotinic ACh receptors or GABA-A). These act much faster (milliseconds) than GPCRs by directly opening an ion channel upon binding. * **D. One-pass receptor:** These are typically **Enzyme-linked receptors** (e.g., Insulin or Growth Factor receptors) which have a single transmembrane helical segment and intrinsic or associated kinase activity. **High-Yield Clinical Pearls for NEET-PG:** * **GPCRs** are the largest family of cell-surface receptors and the target of approximately 40-50% of all modern drugs. * **Gq-coupled:** $\alpha_1$, $M_1$, $M_3$ (Increases $IP_3/DAG$). * **Gi-coupled:** $\alpha_2$, $M_2$, $D_2$ (Inhibits Adenylyl Cyclase). * **Gs-coupled:** All $\beta$ receptors, $D_1$ (Stimulates Adenylyl Cyclase). * **Speed of action:** Ionotropic (Fastest) > GPCR (Intermediate) > Enzyme-linked > Nuclear receptors (Slowest).

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