General Pharmacology Practice Questions

Q: All of the following are involved in the detoxification of drugs EXCEPT:

Cytochrome oxidase. **Explanation:** The detoxification of drugs primarily occurs through the **Microsomal Mixed Function Oxidase (MFO) system**, located in the smooth endoplasmic reticulum of hepatocytes. **Why Cytochrome Oxidase is the Correct Answer:** **Cytochrome oxidase** (also known as Cytochrome c oxidase or Complex IV) is a key enzyme in the **Electron Transport Chain** located in the inner mitochondrial membrane. Its primary role is cellular respiration (reducing oxygen to water to produce ATP), not drug metabolism. Therefore, it is not involved in the detoxification of xenobiotics. **Analysis of Incorrect Options:** * **Cytochrome P450 (CYP450):** This is the most important component of the MFO system. It acts as the terminal oxidase that binds to the drug substrate and molecular oxygen to facilitate oxidation. * **NADPH Cytochrome P450 Reductase:** This enzyme is essential for transferring electrons from NADPH to the Cytochrome P450 molecule, allowing the catalytic cycle to proceed. * **Monooxygenase:** This is a general functional term for the MFO system. These enzymes incorporate one atom of molecular oxygen into the substrate (drug) and reduce the other atom to water. **High-Yield Clinical Pearls for NEET-PG:** * **Phase I Reactions:** Include Oxidation (most common), Reduction, and Hydrolysis. These typically make the drug more polar. * **Phase II Reactions:** Include Glucuronidation (most common), Acetylation, and Methylation. These usually result in inactivation. * **Inducers vs. Inhibitors:** CYP450 **inducers** (e.g., Rifampicin, Phenytoin) decrease the efficacy of co-administered drugs, while **inhibitors** (e.g., Ketoconazole, Erythromycin) increase the risk of toxicity. * **Non-microsomal enzymes:** Some drugs are metabolized by non-microsomal enzymes (e.g., Alcohol dehydrogenase, Xanthine oxidase); these are *not* inducible by drugs.

Q: A manufacturer labels a drug as containing 500mg of paracetamol, but analysis reveals it contains only 200mg. What type of drug is this?

Misbranded drug. ### Explanation The correct answer is **Misbranded drug**. This question tests the definitions provided under the **Drugs and Cosmetics Act (1940)**, which is high-yield for NEET-PG. **1. Why Misbranded Drug is correct:** A drug is classified as **misbranded** if its label is misleading, false, or if the actual content does not match the claims made on the label. In this case, the label claims 500mg, but the actual content is 200mg. It also includes drugs that are not labeled in the prescribed manner or those whose labels do not contain necessary warnings. **2. Why other options are incorrect:** * **Spurious drug:** These are "imitations" or substitutes. A drug is spurious if it is manufactured under a name that belongs to another drug, or if it is a product of a fictitious company. It is essentially a "fake" drug intended to deceive the consumer about its origin. * **Adulterated drug:** This refers to the **quality and purity** of the drug. A drug is adulterated if it consists of filthy, putrid, or decomposed substances, or if it is manufactured under unsanitary conditions that may render it injurious to health. * **Unethical drug:** This is not a legal classification under the Drugs and Cosmetics Act. It is a general term sometimes used for drugs marketed or prescribed in violation of medical ethics. **High-Yield Clinical Pearls for NEET-PG:** * **Misbranded:** Think "Labeling/Quantity error." * **Adulterated:** Think "Contamination/Purity issue." * **Spurious:** Think "Identity theft/Fake origin." * **Schedule H:** Drugs that can be sold only against a prescription of a Registered Medical Practitioner. * **Schedule X:** Narcotic and psychotropic drugs requiring special records and double-copy prescriptions.

Q: All of the following drugs are contraindicated in patients with G-6-PD deficiency, except?

Ceftriaxone. **Explanation:** Glucose-6-Phosphate Dehydrogenase (G6PD) deficiency is an X-linked recessive disorder where RBCs are unable to regenerate NADPH, making them highly susceptible to oxidative stress. When exposed to certain oxidizing agents, hemoglobin precipitates as **Heinz bodies**, leading to acute hemolysis. **Why Ceftriaxone is the correct answer:** Ceftriaxone is a third-generation cephalosporin. Unlike sulfonamides or certain quinolones, cephalosporins do not possess significant oxidizing potential and do not interfere with the pentose phosphate pathway. Therefore, they are safe to use in G6PD-deficient patients. **Analysis of Incorrect Options:** * **Furazolidone:** This is a nitrofuran derivative. Like Nitrofurantoin, it is a potent oxidizing agent that frequently precipitates hemolytic anemia in G6PD-deficient individuals. * **Cotrimoxazole:** This is a combination of Sulfamethoxazole and Trimethoprim. **Sulfonamides** are classic triggers of hemolysis in G6PD deficiency due to their ability to increase free radical production. * **Nalidixic acid:** This is a first-generation quinolone. Quinolones (including older ones like Nalidixic acid and some newer fluoroquinolones) are known to induce oxidative stress in RBCs and are contraindicated. **High-Yield Clinical Pearls for NEET-PG:** * **Mnemonic for G6PD Triggers:** "**AAA**" – **A**ntimalarials (Primaquine, Pamaquine), **A**ntibiotics (Sulfonamides, Nitrofurantoin, Quinolones), and **A**ntipyretics (high-dose Aspirin, Phenazopyridine). * **Other notable triggers:** Dapsone (highest risk), Rasburicase, Methylene blue, and Fava beans (Favism). * **Safe Alternatives:** Penicillins, Cephalosporins, Aminoglycosides, and Acetaminophen (at therapeutic doses) are generally considered safe.

Q: Phase II in a clinical drug trial is done to assess:

Therapeutic efficacy. **Explanation:** Clinical trials are conducted in four distinct phases to ensure the safety and efficacy of a new drug before and after it reaches the market. **Phase II (Therapeutic Exploration)** is primarily designed to assess **therapeutic efficacy** in a small group of patients (100–300) who actually have the target disease. This phase helps determine the dose range, ceiling effect, and confirms that the drug produces the intended clinical result. **Analysis of Options:** * **Option A (Correct):** Phase II evaluates if the drug works in patients. It is often divided into Phase IIa (pilot studies for efficacy) and Phase IIb (pivotal trials to determine the optimum dose). * **Option B (Incorrect):** The **Maximum Tolerated Dose (MTD)** is determined in **Phase I** (Therapeutic Orphan phase), usually involving healthy volunteers. * **Option C (Incorrect):** The **Lethal Dose (LD50)** is determined during **pre-clinical animal studies**, not in human clinical trials. * **Option D (Incorrect):** While safety is monitored in all phases, the primary screening for **safety and toxicity** occurs in **Phase I**. **High-Yield Clinical Pearls for NEET-PG:** * **Phase I:** Safety, Tolerability, and Pharmacokinetics (Healthy volunteers, except for oncology drugs). * **Phase III:** Therapeutic Confirmation (Large-scale, multicentric, randomized controlled trials). * **Phase IV:** Post-marketing surveillance (Detects rare adverse effects like Phocomelia or Rofecoxib-induced cardiotoxicity). * **Phase 0:** Human microdosing studies to determine PK parameters using AMS (Accelerator Mass Spectrometry).

Q: According to the Drugs and Cosmetics Rules, which schedule does the following drug belong to?

Schedule C. ***Schedule C*** - **Schedule C** under the Drugs and Cosmetics Rules 1945 covers **biological and special products** including vaccines, sera, toxoids, blood products, and insulin. - These products require **special licensing and testing requirements** due to their biological nature and potential safety concerns. *Schedule B* - **Schedule B** deals with **fees for testing** of drugs and cosmetics by government laboratories. - It does not classify specific drug categories but rather outlines the **financial requirements** for drug testing procedures. *Schedule J* - **Schedule J** lists **diseases and conditions** for which no person can claim a cure through drug advertisements. - It focuses on **advertisement restrictions** rather than drug classification, including conditions like cancer, diabetes, and heart disease. *Schedule G* - **Schedule G** contains drugs that must bear the warning **"To be sold by retail on the prescription of a Registered Medical Practitioner only"**. - It covers **prescription-only medicines** requiring medical supervision, not biological products like vaccines or sera.

Q: The fall in blood pressure caused by d-tubocurarine is due to which of the following mechanisms?

All of the above. **Explanation:** **d-Tubocurarine (d-TC)** is a prototype non-depolarizing neuromuscular blocker that causes a significant fall in blood pressure through a multi-factorial mechanism: 1. **Histamine Release:** d-TC is a potent inducer of mast cell degranulation. The released histamine causes systemic vasodilation and increased capillary permeability, leading to a drop in peripheral vascular resistance and blood pressure. 2. **Ganglionic Blockade:** At therapeutic doses, d-TC can block nicotinic receptors ($N_n$) at the autonomic ganglia. This reduces sympathetic outflow to the blood vessels, further contributing to hypotension. 3. **Reduced Venous Return:** The drug causes profound skeletal muscle relaxation. The loss of the "skeletal muscle pump" action, combined with the vasodilation mentioned above, leads to peripheral pooling of blood and a subsequent decrease in venous return to the heart. **Why "All of the above" is correct:** Since d-TC simultaneously triggers histamine release, inhibits autonomic ganglia, and reduces the muscle pump effect, all three mechanisms synergistically contribute to the observed hypotension. **Clinical Pearls for NEET-PG:** * **Mnemonic:** d-Tubocurarine "**T**errible" for BP (Histamine + Ganglia). * **Modern Alternatives:** Newer agents like **Vecuronium** and **Rocuronium** are preferred in clinical practice because they lack histamine-releasing and ganglion-blocking properties, making them cardiovascularly stable. * **Atracurium:** Also causes histamine release but is unique for its metabolism via **Hofmann elimination** (spontaneous degradation), making it safe in liver and kidney failure. * **Antidote:** Hypotension caused by d-TC is managed with fluids and vasopressors, while the neuromuscular block is reversed using **Neostigmine** (plus Glycopyrrolate).

Q: Which of the following are prodrugs?

All of these. **Explanation:** A **prodrug** is a pharmacologically inactive compound that must undergo chemical or enzymatic biotransformation within the body to be converted into its active metabolite. This strategy is often used to improve bioavailability, reduce toxicity, or enhance site-specificity. * **Mercaptopurine (Option A):** This is a purine analogue used in leukemia. It is inactive in its parent form and must be converted by the enzyme **HGPRT** into **6-thioinosinic acid** (the active nucleotide) to inhibit DNA synthesis. * **Dipivefrine (Option B):** It is a prodrug of **Epinephrine** used in glaucoma. Being more lipophilic than epinephrine, it penetrates the cornea much more effectively. Once inside the eye, it is hydrolyzed by esterases into active epinephrine. * **Enalapril (Option C):** Most ACE inhibitors (except Captopril and Lisinopril) are prodrugs. Enalapril is converted by hepatic esterases into **Enalaprilat**, which is the potent inhibitor of the Angiotensin-Converting Enzyme. Since all three medications require metabolic activation, **Option D** is the correct answer. **High-Yield Clinical Pearls for NEET-PG:** * **Mnemonic for Prodrugs:** "**A**ll **P**rodrugs **C**an **E**nter **D**e **L**iver **M**aking **S**ome **P**otent **H**ormones" (**A**CEIs (except Capto/Lisino), **P**roton Pump Inhibitors, **C**yclophosphamide, **E**nalapril, **D**opa (L-Dopa), **L**evodopa, **M**ercaptopurine, **S**ulindac, **P**rednisone, **H**eroin). * **Exceptions:** **Captopril and Lisinopril** are the only ACE inhibitors that are **NOT** prodrugs. * **Advantage:** Prodrugs like **Levodopa** can cross the blood-brain barrier, whereas the active form (Dopamine) cannot.

Question 1

All of the following are involved in the detoxification of drugs EXCEPT:

Accepted Answer

Cytochrome oxidase

Answer

NADPH cytochrome P450 reductase

Answer

Cytochrome P450

Answer

Monooxygenase

Question 2

A manufacturer labels a drug as containing 500mg of paracetamol, but analysis reveals it contains only 200mg. What type of drug is this?

Accepted Answer

Misbranded drug

Answer

Spurious drug

Answer

Adulterated drug

Answer

Unethical drug

Question 3

All of the following actions of histamine are mediated through H1 receptors EXCEPT?

Accepted Answer

Direct action on vascular smooth muscle causing vasodilation

Answer

Release of EDRF from vascular endothelium resulting in vasodilation

Answer

Bronchoconstriction

Answer

Release of catecholamines from adrenal medulla

Question 4

All of the following drugs are contraindicated in patients with G-6-PD deficiency, except?

Accepted Answer

Ceftriaxone

Answer

Furazolidone

Answer

Cotrimoxazole

Answer

Nalidixic acid

Question 5

Phase II in a clinical drug trial is done to assess:

Accepted Answer

Therapeutic efficacy

Answer

Maximal tolerated dose

Answer

Maximal lethal dose

Answer

Toxicity

Question 6

Which of the following is NOT a Category X drug?

Accepted Answer

Alprazolam

Answer

Warfarin

Answer

Methotrexate

Answer

Simvastatin

Question 7

According to the Drugs and Cosmetics Rules, which schedule does the following drug belong to?

Accepted Answer

Schedule C

Answer

Schedule B

Answer

Schedule J

Answer

Schedule G

Question 8

The fall in blood pressure caused by d-tubocurarine is due to which of the following mechanisms?

Accepted Answer

All of the above

Answer

Reduced venous return

Answer

Ganglionic blockade

Answer

Histamine release

Question 9

Tolerance and physical dependence may occur after chronic use of all of the following agents EXCEPT?

Accepted Answer

Clomipramine

Answer

Meperidine

Answer

Phenobarbital

Answer

Diazepam

Question 10

Which of the following are prodrugs?

Accepted Answer

All of these

Answer

Mercaptopurine

Answer

Dipivefrine

Answer

Enalapril

General Pharmacology — MCQs

General Pharmacology — MCQs

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