General Pharmacology — MCQs

General Pharmacology Indian Medical PG Practice Questions and MCQs

Question 31: Which of the following neuromuscular blocking agents can be safely administered in patients with hepatic as well as renal failure?

A. Atracurium (Correct Answer)
B. Vecuronium
C. Pancuronium
D. Mivacurium

Explanation: **Explanation:** The correct answer is **Atracurium**. **Why Atracurium is correct:** Atracurium (and its isomer Cisatracurium) is unique among neuromuscular blockers because it does not rely on hepatic metabolism or renal excretion for its clearance. Instead, it undergoes **Hofmann elimination**—a spontaneous, non-enzymatic degradation at physiological pH and temperature—and ester hydrolysis by non-specific plasma esterases. This makes it the drug of choice for patients with multi-organ failure (hepatic and renal impairment). **Why the other options are incorrect:** * **Vecuronium:** It is primarily metabolized by the liver (deacetylation) and excreted in bile (40-50%) and urine. Its duration of action is significantly prolonged in patients with hepatic or renal dysfunction. * **Pancuronium:** This is a long-acting agent primarily excreted unchanged by the kidneys (up to 80%). It is contraindicated in renal failure due to the high risk of accumulation and prolonged paralysis. * **Mivacurium:** While it is metabolized by plasma pseudocholinesterase (similar to Succinylcholine), its clearance can be delayed in liver disease due to reduced synthesis of the pseudocholinesterase enzyme. **High-Yield Clinical Pearls for NEET-PG:** * **Laudanosine Toxicity:** A major metabolite of Atracurium is Laudanosine. In high concentrations (especially during long infusions), it can cross the blood-brain barrier and act as a **CNS stimulant**, potentially causing seizures. * **Cisatracurium:** It is more potent than Atracurium, undergoes Hofmann elimination, but produces significantly **less Laudanosine**, making it safer for long-term ICU infusions. * **Histamine Release:** Atracurium can cause histamine release, leading to hypotension and bronchospasm; Cisatracurium does not.

Question 32: Which of the following is a long-acting classical H1 antihistamine?

A. Chlorpheniramine (Correct Answer)
B. Astemizole
C. Cetirizine
D. Clemastine

Explanation: **Explanation:** The question asks for a **long-acting classical (1st generation)** H1 antihistamine. **1. Why Chlorpheniramine is Correct:** Chlorpheniramine is a potent 1st-generation antihistamine belonging to the alkylamine class. While many 1st-generation drugs (like Diphenhydramine) have a short duration of action (4–6 hours), Chlorpheniramine is characterized by a relatively long half-life (~20–24 hours in adults), allowing for less frequent dosing. It is "classical" because it crosses the blood-brain barrier, causing sedation and anticholinergic side effects. **2. Analysis of Incorrect Options:** * **Astemizole:** This is a **2nd-generation** antihistamine. While it is exceptionally long-acting (half-life of days), it is no longer used clinically due to the risk of fatal arrhythmias (*Torsades de Pointes*) caused by QT interval prolongation. * **Cetirizine:** This is a **2nd-generation** antihistamine (a metabolite of Hydroxyzine). It is "non-sedating" (or minimally sedating) and does not fall under the "classical" category. * **Clemastine:** This is a 1st-generation antihistamine (ethanolamine class). However, it generally has a shorter duration of action compared to the sustained effect of Chlorpheniramine. **3. NEET-PG High-Yield Pearls:** * **1st Gen vs. 2nd Gen:** 1st generation drugs are lipophilic (cross BBB) and cause sedation/anticholinergic effects. 2nd generation drugs are lipophobic and lack these effects. * **Cardiac Toxicity:** Astemizole and Terfenadine were withdrawn because they inhibit delayed rectifier K+ channels in the heart. * **Active Metabolites:** Fexofenadine is the active metabolite of Terfenadine; Cetirizine is the active metabolite of Hydroxyzine; Loratadine is metabolized to Desloratadine. * **Drug of Choice:** Chlorpheniramine is often the preferred antihistamine for allergic reactions in pregnancy (Category B).

Question 33: Which of the following drugs affects CYP 3A4 enzymes?

A. Fexofenadine
B. Phenytoin
C. Carbamazepine (Correct Answer)
D. Azithromycin

Explanation: **Explanation:** The Cytochrome P450 (CYP) enzyme system is the primary pathway for drug metabolism in the liver. **Carbamazepine** is a potent **inducer** of the CYP 3A4 isoenzyme. As an auto-inducer, it not only increases the metabolism of co-administered drugs (like oral contraceptives or warfarin) but also enhances its own metabolism over time. **Analysis of Options:** * **Carbamazepine (Correct):** A classic enzyme inducer. It increases the synthesis of CYP 3A4, leading to decreased plasma levels of substrate drugs. * **Fexofenadine:** This is a second-generation antihistamine known for being "metabolically inert." It is excreted largely unchanged in the urine and feces and does not significantly interact with CYP enzymes. * **Phenytoin:** While Phenytoin is a potent general enzyme inducer, it primarily induces **CYP 2C9 and 2C19**. While it has some effect on 3A4, Carbamazepine is the more characteristic answer in the context of 3A4-specific questions in standard pharmacology curricula. * **Azithromycin:** Unlike other macrolides (Erythromycin and Clarithromycin), Azithromycin **does not** inhibit CYP 3A4. This makes it a safer choice in patients taking drugs with narrow therapeutic indices. **High-Yield Clinical Pearls for NEET-PG:** 1. **CYP 3A4 Inducers (Mnemonic: GPRS Cell Phone):** **G**riseofulvin, **P**henytoin, **R**ifampicin, **S**moking, **C**arbamazepine, **P**henobarbitone. 2. **CYP 3A4 Inhibitors (Mnemonic: VITAMIN G):** **V**erapamil, **I**traconazole, **T**elithromycin, **A**miodarone, **M**acrolides (except Azithromycin), **I**ndinavir, **N**efazodone, **G**rapefruit juice. 3. **Carbamazepine** is the drug of choice for Trigeminal Neuralgia but requires monitoring for Stevens-Johnson Syndrome (especially in HLA-B*1502 positive patients).

Question 34: Which teratogen is known to cause deafness?

A. Isotretinoin (Correct Answer)
B. Chloroquine
C. Alcohol
D. Warfarin

Explanation: **Explanation:** **Isotretinoin (Option A)** is a highly potent teratogen used for severe acne. It causes a specific pattern of malformations known as **Retinoic Acid Embryopathy**. This occurs due to its interference with neural crest cell migration. Key features include **craniofacial abnormalities**, **microtia/anotia** (small or absent ears), and **congenital deafness** (sensorineural hearing loss). It also causes CNS defects and cardiovascular malformations (e.g., Transposition of Great Arteries). **Why other options are incorrect:** * **Chloroquine (Option B):** While it can cross the placenta, it is generally considered safe in pregnancy for malaria prophylaxis. High doses have been historically linked to eighth nerve damage, but it is not the classic association for deafness compared to Isotretinoin or Aminoglycosides. * **Alcohol (Option C):** Causes **Fetal Alcohol Syndrome (FAS)**, characterized by maxillary hypoplasia, smooth philtrum, thin upper lip, microcephaly, and mental retardation, but not typically primary deafness. * **Warfarin (Option D):** Causes **Fetal Warfarin Syndrome**, characterized by **nasal hypoplasia**, depressed nasal bridge, and stippled epiphyses (chondrodysplasia punctata). **High-Yield Clinical Pearls for NEET-PG:** * **Isotretinoin Rule:** Female patients must follow the **iPLEDGE program**, requiring two forms of contraception and a negative pregnancy test before starting therapy. * **Thalidomide:** Causes Phocomelia (seal-like limbs). * **Valproate:** Highest risk for Neural Tube Defects (Meningomyelocele). * **Phenytoin:** Fetal Hydantoin Syndrome (hypoplastic nails and phalanges). * **Aminoglycosides (e.g., Streptomycin):** Another major cause of ototoxicity/deafness in utero.

Question 35: When a drug binds to a receptor and causes an action opposite to that of an agonist, what is this called?

A. Complete Agonist
B. Partial Agonist
C. Inverse agonist (Correct Answer)
D. Neutral antagonist

Explanation: ### Explanation **1. Why "Inverse Agonist" is Correct:** In pharmacology, receptors often exhibit **constitutive activity**, meaning they produce a baseline biological response even in the absence of a ligand. An **Inverse Agonist** binds to the same receptor as an agonist but stabilizes the inactive form, thereby reducing the constitutive activity. This results in a pharmacological effect that is **directionally opposite** to that of the agonist (negative efficacy). **2. Analysis of Incorrect Options:** * **A. Complete (Full) Agonist:** Binds to the receptor and produces the maximum possible biological response (100% efficacy). * **B. Partial Agonist:** Binds to the receptor but produces a sub-maximal response, even at full receptor occupancy. It acts as an antagonist in the presence of a full agonist. * **D. Neutral Antagonist:** Binds to the receptor but has **zero intrinsic activity**. It does not produce a response of its own; it simply blocks the agonist from binding. It does not affect the constitutive activity. **3. NEET-PG High-Yield Clinical Pearls:** * **Classic Examples of Inverse Agonists:** * **Beta-carbolines** (at GABA-A receptors): Cause anxiety and convulsions (opposite to Benzodiazepines). * **Famotidine** (H2 receptors). * **Losartan** (AT1 receptors). * **Naloxone** (at Mu-opioid receptors). * **Key Distinction:** While an antagonist has **zero** efficacy, an inverse agonist has **negative** efficacy. * **Concept Check:** If a receptor has no constitutive activity, an inverse agonist will behave exactly like a neutral antagonist.

Question 36: Which one of the following drugs does not have an active metabolite?

A. Diazepam
B. Propanolol
C. Allopurinol
D. Lisinopril (Correct Answer)

Explanation: **Explanation:** The correct answer is **Lisinopril**. The underlying concept involves understanding **Prodrugs** and **Active Metabolites**. Most ACE inhibitors (like Enalapril or Ramipril) are prodrugs that require hepatic conversion into their active "-at" forms (e.g., Enalaprilat). However, **Lisinopril and Captopril** are the two notable exceptions; they are active drugs themselves and do not undergo metabolism to form active metabolites. Lisinopril is excreted unchanged in the urine. **Analysis of Incorrect Options:** * **Diazepam:** A classic example of a drug with multiple long-lived active metabolites, including **Desmethyldiazepam (Nordiazepam)**, Temazepam, and Oxazepam. This contributes to its prolonged duration of action. * **Propranolol:** It undergoes extensive first-pass metabolism to form **4-hydroxypropranolol**, which possesses beta-blocking activity similar to the parent compound. * **Allopurinol:** It is rapidly metabolized by xanthine oxidase to **Alloxanthine (Oxypurinol)**. Alloxanthine is a potent, non-competitive inhibitor of xanthine oxidase and is responsible for the majority of the drug's long-term clinical effect. **NEET-PG High-Yield Pearls:** * **ACE Inhibitor Exceptions:** Remember the mnemonic **"CL"** (Captopril and Lisinopril) as the ACE inhibitors that are **NOT** prodrugs. * **Lisinopril** is preferred in patients with liver disease because it does not require hepatic activation. * **Active Metabolite of Spironolactone:** Canrenone. * **Active Metabolite of Morphine:** Morphine-6-glucuronide (more potent than morphine). * **Prodrug of Epinephrine:** Dipivefrine (used in glaucoma).

Question 37: GABA-B receptors are:

A. G-protein coupled receptors (Correct Answer)
B. Intrinsic ion channel
C. Enzyme linked receptors
D. Ligand gated ion channels

Explanation: **Explanation:** The correct answer is **A. G-protein coupled receptors.** **Understanding GABA Receptors:** Gamma-aminobutyric acid (GABA) is the primary inhibitory neurotransmitter in the central nervous system. It acts through two distinct types of receptors: GABA-A and GABA-B. * **GABA-B receptors** are metabotropic receptors [1]. They are **G-protein coupled receptors (GPCRs)** linked to $G_i/G_o$ proteins [2]. Their activation leads to the inhibition of adenylyl cyclase, opening of potassium ($K^+$) channels (causing hyperpolarization), and closing of voltage-gated calcium ($Ca^{2+}$) channels (inhibiting neurotransmitter release) [2]. * **GABA-A receptors**, conversely, are **ligand-gated ion channels** (ionotropic) [2]. They are pentameric structures that directly control a chloride ($Cl^-$) channel, leading to rapid inhibitory postsynaptic potentials [2]. **Analysis of Incorrect Options:** * **B & D (Intrinsic/Ligand-gated ion channels):** These describe **GABA-A** receptors. GABA-B does not have an intrinsic pore; it requires a second messenger system. * **C (Enzyme-linked receptors):** These are typically receptors for growth factors (e.g., Insulin, EGF) and involve tyrosine kinase activity, which is unrelated to GABA signaling. **High-Yield Clinical Pearls for NEET-PG:** * **Baclofen** is a selective **GABA-B agonist** used clinically as a centrally acting muscle relaxant to treat spasticity (e.g., in Multiple Sclerosis). * **GABA-A** is the target for Benzodiazepines, Barbiturates, and Alcohol. * **GABA-C** (now considered a subtype of GABA-A) is also a ligand-gated chloride channel, found primarily in the retina. * **Memory Aid:** GABA-**B** is **B**oth G-protein linked and targeted by **B**aclofen.

Question 38: Which of the following is a prodrug?

A. Phenytoin
B. Carbamazepine
C. Primidone (Correct Answer)
D. Valproic acid

Explanation: **Explanation:** **Primidone** is a classic example of a **prodrug** in the context of antiepileptic therapy. A prodrug is a pharmacologically inactive (or less active) compound that must undergo metabolic conversion within the body to become therapeutically active. Primidone is metabolized by the hepatic microsomal enzymes into two active metabolites: 1. **Phenobarbital:** A long-acting barbiturate. 2. **Phenylethylmalonamide (PEMA):** Also possesses anticonvulsant activity. The clinical efficacy of Primidone is largely attributed to the accumulation of these active metabolites, particularly Phenobarbital. **Analysis of Incorrect Options:** * **A. Phenytoin:** This is an active drug. It does not require metabolic activation to exert its effect on voltage-gated sodium channels. It is notable for its zero-order kinetics at high doses. * **B. Carbamazepine:** This is an active drug. While it has an active metabolite (Carbamazepine-10,11-epoxide), the parent drug itself is therapeutically active. It is also a potent enzyme inducer. * **D. Valproic Acid:** This is an active drug. It acts directly through multiple mechanisms, including GABA enhancement and sodium channel blockade. **High-Yield Clinical Pearls for NEET-PG:** * **Fosphenytoin** is the prodrug of Phenytoin (used IV to avoid the local irritation/Purple Glove Syndrome associated with Phenytoin). * **Levodopa** is a classic prodrug (converted to Dopamine). * **Enalapril** is a prodrug (converted to Enalaprilat). * **Pro-drugs are often designed** to improve bioavailability, reduce side effects, or enhance selective delivery to the target site.

Question 39: Idiosyncrasy is known to have which of the following components?

A. Genetic component (Correct Answer)
B. Psychological component
C. Physiological component
D. Nutritional component

Explanation: ### Explanation **1. Why Option A is Correct:** **Idiosyncrasy** (or Type B adverse drug reaction) refers to a genetically determined abnormal reactivity to a chemical or drug. Unlike standard side effects, these reactions are **unpredictable**, do not occur in most patients, and are not dose-dependent. The underlying mechanism is typically a **genetic polymorphism** involving drug-metabolizing enzymes or receptors. For example, a patient with a G6PD deficiency (a genetic trait) will experience hemolysis when given Primaquine; this is a classic idiosyncratic reaction. **2. Why Other Options are Incorrect:** * **B. Psychological component:** This refers to the **Placebo effect** (positive response) or **Nocebo effect** (negative response) based on the patient's expectations, rather than a biological reaction to the drug molecule itself. * **C. Physiological component:** Physiological factors include age, sex, or pregnancy, which influence drug pharmacokinetics (e.g., slower metabolism in neonates) but do not define the unique, "bizarre" nature of idiosyncrasy. * **D. Nutritional component:** While malnutrition can affect protein binding or liver function, it does not account for the specific, genetically-coded abnormal responses characteristic of idiosyncrasy. **3. NEET-PG High-Yield Pearls:** * **Type B Reactions:** Remember the mnemonic **"B" for Bizarre.** Idiosyncratic reactions are Type B (unpredictable, non-dose-related, high morbidity/mortality). * **Classic Examples:** * **Succinylcholine apnea:** Due to a genetic deficiency of pseudocholinesterase. * **Malignant Hyperthermia:** Triggered by Halothane/Succinylcholine due to a mutation in the *RYR1* (Ryanodine) receptor. * **Aplastic Anemia:** Caused by Chloramphenicol (idiosyncratic in most cases). * **Distinction:** Unlike allergies, idiosyncratic reactions do not require prior sensitization (no IgE involvement).

Question 40: Steady state concentration is typically achieved in how many half-lives?

A. 3
B. 4
C. 5 (Correct Answer)
D. 6

Explanation: **Explanation:** The concept of **Steady State Concentration ($C_{ss}$)** refers to the point during a drug’s administration where the rate of drug elimination equals the rate of drug administration. In first-order kinetics, this is a time-dependent process determined solely by the drug’s half-life ($t_{1/2}$). **Why Option C is Correct:** Mathematically, a drug reaches a specific percentage of its final steady-state concentration with each passing half-life: * 1 $t_{1/2}$: 50% * 2 $t_{1/2}$: 75% * 3 $t_{1/2}$: 87.5% * 4 $t_{1/2}$: 93.75% * **5 $t_{1/2}$: 96.875%** In clinical pharmacology, reaching **>95%** of the steady state is considered functionally complete. Therefore, it takes approximately **4 to 5 half-lives** to reach steady state. Since "5" is the standard benchmark in most textbooks (like Katzung and K.D. Tripathi) for achieving a stable therapeutic level, it is the preferred answer. **Why Other Options are Incorrect:** * **Option A (3 $t_{1/2}$):** Only 87.5% of the drug is accumulated; the plasma concentration is still rising significantly. * **Option B (4 $t_{1/2}$):** While 93.75% is close, 5 half-lives ensure the concentration is more stable and closer to the ultimate plateau. * **Option D (6 $t_{1/2}$):** While the drug is certainly at steady state by 6 half-lives, it is not the *earliest* point at which steady state is typically defined. **High-Yield NEET-PG Pearls:** 1. **Loading Dose:** To achieve therapeutic levels immediately without waiting for 5 half-lives, a loading dose is administered. 2. **Washout Period:** Similarly, it takes **5 half-lives** for a drug to be completely eliminated (97% cleared) from the body after stopping administration. 3. **Independence:** The time to reach steady state is **independent of the dose**; increasing the dose will increase the final concentration level but will not change the time (number of half-lives) taken to get there.

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