Which of the following are CYP3A inhibitors?
Regarding the concepts of efficacy and potency of a drug, which of the following statements is FALSE?
Volume of distribution of a drug is 500 ml and target concentration of drug in blood is 5 g/L. 20% of administered drug is reached to systemic circulation. What will be the loading dose of that drug -
High volume of distribution is primarily determined by:
All of the following are known adverse effects of thalidomide, except:
Which statement best describes first-order kinetics in pharmacokinetics?
Which of the following conditions is not associated with an increased risk of neuropathy caused by Isoniazid (INH)?
Idoxuridine is used for treatment of?
What is the best method for treating methanol poisoning?
Interstitial nephritis is associated with all of the following medications except:
NEET-PG 2015 - Pharmacology NEET-PG Practice Questions and MCQs
Question 81: Which of the following are CYP3A inhibitors?
- A. Ritonavir
- B. Amiodarone
- C. Verapamil
- D. Both a and c (Correct Answer)
Explanation: ***Both a and c (Ritonavir and Verapamil)*** - **Ritonavir** is a **potent CYP3A4 inhibitor**, one of the strongest known, commonly used as a pharmacokinetic booster for other protease inhibitors to increase their bioavailability - **Verapamil** is a **calcium channel blocker** that acts as a **moderate CYP3A4 inhibitor**, leading to clinically significant drug interactions requiring dose adjustments - Both drugs have **clinically relevant and well-established** CYP3A4 inhibitory effects *Ritonavir alone* - While correct that Ritonavir is a potent CYP3A4 inhibitor, this option is incomplete as it excludes Verapamil - Ritonavir's inhibitory effect is so strong that it can increase plasma concentrations of co-administered CYP3A4 substrates by several-fold *Amiodarone* - Amiodarone is primarily a **potent inhibitor of CYP2C9, CYP2D6, and P-glycoprotein** - While it does have **weak to moderate CYP3A4 inhibitory activity**, this effect is **less clinically significant** compared to its effects on other CYP enzymes - In the context of clinically important CYP3A4 inhibitors, Ritonavir and Verapamil are more relevant examples *Verapamil alone* - While correct that Verapamil is a CYP3A4 inhibitor, this option is incomplete as it excludes Ritonavir - Verapamil can increase plasma concentrations of drugs like simvastatin, cyclosporine, and other CYP3A4 substrates
Question 82: Regarding the concepts of efficacy and potency of a drug, which of the following statements is FALSE?
- A. ED50 of the drug corresponds to efficacy (Correct Answer)
- B. Drugs that produce a similar pharmacological effect can have different levels of efficacy
- C. In a clinical setup, efficacy is more important than potency
- D. In the log dose response curve, the height of the curve corresponds with efficacy
Explanation: ***ED50 of the drug corresponds to efficacy*** - **ED50** (median effective dose) is the dose at which 50% of individuals exhibit the specified effect; it quantifies **potency**, not efficacy. - **Efficacy** refers to the maximum effect a drug can produce, while potency refers to the amount of drug needed to produce an effect. *In a clinical setup, efficacy is more important than potency* - **Efficacy** determines the maximal therapeutic benefit a drug can achieve for a patient, making it crucial for clinical outcomes. - While **potency** influences the dose required, a highly potent drug that is not very efficacious may not be clinically useful. *Drugs that produce a similar pharmacological effect can have different levels of efficacy* - Two drugs might act on the same receptor but elicit different maximal responses, indicating varying **efficacy**. - For example, a **partial agonist** and **full agonist** interacting with the same receptor will have different efficacies. *In the log dose response curve, the height of the curve corresponds with efficacy* - The **maximal response** or plateau of the dose-response curve represents the **efficacy** of a drug. - A higher plateau on the curve indicates a drug with greater intrinsic activity achieving a larger effect.
Question 83: Volume of distribution of a drug is 500 ml and target concentration of drug in blood is 5 g/L. 20% of administered drug is reached to systemic circulation. What will be the loading dose of that drug -
- A. 1 gm
- B. 5 gm
- C. 25 gm
- D. 12.5 gm (Correct Answer)
Explanation: ***12.5 gm*** - The formula for loading dose (LD) is: LD = (Target Concentration × Volume of Distribution) / Bioavailability. - Given: Target Concentration = 5 g/L, Volume of Distribution = 500 mL = 0.5 L, Bioavailability = 20% = 0.2. - So, LD = (5 g/L × 0.5 L) / 0.2 = 2.5 g / 0.2 = **12.5 g**. *1 gm* - This value would be obtained if the target concentration was 2 g/L with 100% bioavailability, or if the calculation incorrectly handled the volume or bioavailability factor. - It does not account for the specified **bioavailability of 20%** or the given target concentration and volume of distribution. *5 gm* - This result would be obtained if the bioavailability was assumed to be 50% (LD = 2.5 g / 0.5 = 5 g), or if the volume of distribution was incorrectly used in the calculation. - This option does not correctly factor in the **20% bioavailability** of the administered drug. *25 gm* - This value would result from mistakes such as dividing by bioavailability of 10% instead of 20% (LD = 2.5 g / 0.1 = 25 g), or by multiplying bioavailability instead of dividing by it. - This answer significantly **overestimates** the required dose, which could lead to drug toxicity.
Question 84: 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 85: All of the following are known adverse effects of thalidomide, except:
- A. DVT
- B. Neuropathy
- C. Teratogenicity
- D. Diarrhoea (Correct Answer)
Explanation: ***Diarrhoea*** - **Diarrhoea** is generally *not* considered a common or significant adverse effect of thalidomide. Constipation is more frequently reported. - While individual reactions vary, thalidomide's primary adverse effect profile does not typically include diarrhoea. *Teratogenicity* - **Teratogenicity** is the most notorious adverse effect of thalidomide, causing severe birth defects like **phocomelia** (shortened or absent limbs) in infants exposed during pregnancy. - Due to this, stringent **risk evaluation and mitigation strategies (REMS)** are in place for thalidomide use. *DVT* - Thalidomide is known to increase the risk of **venous thromboembolism (VTE)**, including **deep vein thrombosis (DVT)** and pulmonary embolism, especially in patients with multiple myeloma. - Prophylactic anticoagulation is often recommended for patients receiving thalidomide, particularly in combination with corticosteroids. *Neuropathy* - **Peripheral neuropathy** is a common and dose-limiting adverse effect of thalidomide, often presenting as numbness, tingling, and pain in the hands and feet. - It can be progressive and potentially irreversible, requiring careful monitoring and dose adjustments.
Question 86: Which statement best describes first-order kinetics in pharmacokinetics?
- A. Absorption of the drug is independent of the serum concentration
- B. Elimination of the drug is proportional to the serum concentration (Correct Answer)
- C. Absorption of the drug is proportional to the serum concentration
- D. Elimination of the drug is independent of the serum concentration
Explanation: ***Elimination of the drug is proportional to the serum concentration*** - In **first-order kinetics**, a **constant fraction** (or percentage) of the drug is eliminated per unit of time. - This means that as the **serum drug concentration** increases, the absolute amount of drug eliminated per unit time also increases proportionally. *Absorption of the drug is independent of the serum concentration* - Drug absorption is generally driven by factors like **concentration gradient**, surface area, and blood flow, and while it can be influenced by drug concentration, this statement does not define first-order kinetics of *elimination*. - This statement is not the primary characteristic distinguishing first-order from zero-order kinetics regarding drug disposition. *Elimination of the drug is independent of the serum concentration.* - This describes **zero-order kinetics**, where a **constant amount** of drug is eliminated per unit of time, regardless of the serum concentration. - In zero-order kinetics, the elimination rate becomes saturated, so the elimination process cannot keep up with higher drug concentrations. *Absorption of the drug is proportional to the serum concentration* - While drug absorption can be proportional to the concentration (especially through passive diffusion), first-order kinetics specifically refers to the **elimination phase** of pharmacokinetics. - The rate of absorption can be a complex process and is not the defining characteristic for distinguishing first-order from zero-order *elimination*.
Question 87: Which of the following conditions is not associated with an increased risk of neuropathy caused by Isoniazid (INH)?
- A. Uremia
- B. Diabetes mellitus
- C. Poor nutrition
- D. Hyperthyroidism (Correct Answer)
Explanation: ***Hyperthyroidism*** - **Hyperthyroidism** is not typically associated with an increased risk of isoniazid-induced neuropathy. The neuropathy due to INH is primarily linked to **pyridoxine (vitamin B6) deficiency**. - While hyperthyroidism can cause its own set of neurological symptoms, it does not directly impair pyridoxine metabolism or exacerbate INH's neurotoxic effects. *Uremia* - **Uremia** (renal failure) can increase the risk of INH-induced neuropathy due to impaired drug excretion, leading to higher plasma concentrations of INH and its metabolites. - Patients with uremia often have compromised nutritional status and may experience vitamin deficiencies, further contributing to pyridoxine depletion. *Diabetes mellitus* - **Diabetes mellitus** is a significant risk factor for INH-induced neuropathy because it is an independent cause of **peripheral neuropathy** itself, making patients more susceptible to additional nerve damage. - Diabetic patients may also have altered pyridoxine metabolism or suboptimal nutritional intake, predisposing them to INH toxicity. *Poor nutrition* - **Poor nutrition**, particularly malabsorption or inadequate dietary intake, directly contributes to **pyridoxine (vitamin B6) deficiency**. - Isoniazid's mechanism of neurotoxicity involves interfering with pyridoxine metabolism, so pre-existing deficiency significantly increases the risk of neuropathy.
Question 88: Idoxuridine is used for treatment of?
- A. Influenza
- B. RSV
- C. HSV (Correct Answer)
- D. HIV
Explanation: ***HSV*** - **Idoxuridine** is a **pyrimidine analog** that inhibits viral DNA synthesis, making it effective against **herpes simplex virus (HSV)** infections, particularly **herpes keratitis** (ophthalmic use). - Its mechanism involves being incorporated into viral DNA, leading to errors in replication and transcription. - It is applied **topically** for ocular HSV infections due to systemic toxicity concerns. *Influenza* - **Idoxuridine** is not active against **influenza viruses**. - **Antiviral drugs** like **oseltamivir** or **zanamivir** are typically used for influenza treatment. *RSV* - **Idoxuridine** is not indicated for the treatment of **respiratory syncytial virus (RSV)**. - **Ribavirin** is the primary antiviral agent used for severe RSV infections, especially in immunocompromised patients. *HIV* - **Idoxuridine** has no significant activity against **human immunodeficiency virus (HIV)**. - **Antiretroviral therapy (ART)**, a combination of drugs targeting various stages of the HIV life cycle, is used for HIV treatment.
Question 89: What is the best method for treating methanol poisoning?
- A. Calcium gluconate
- B. BAL
- C. Fomepizole (Correct Answer)
- D. Deferoxamine
Explanation: ***Fomepizole*** - **Fomepizole** (Antizol) is a potent inhibitor of **alcohol dehydrogenase**, the enzyme responsible for metabolizing methanol into toxic metabolites like formic acid [1]. - By inhibiting this enzyme, fomepizole prevents the formation of these harmful metabolites, thus halting the progression of methanol toxicity and reducing mortality [1]. - It is the **gold standard** antidote for methanol poisoning. *Calcium gluconate* - **Calcium gluconate** is primarily used to treat **hypocalcemia** and magnesium toxicity. - It has no role in the direct treatment or detoxification of methanol poisoning. *Deferoxamine* - **Deferoxamine** is a **chelating agent** used to treat **iron toxicity** by binding to iron and facilitating its excretion [3]. - It is not effective for methanol poisoning as it does not interact with methanol or its toxic metabolites. *BAL* - **BAL** (British Anti-Lewisite, dimercaprol) is a chelating agent primarily used for poisoning by **heavy metals** such as arsenic, mercury, and gold [2]. - It has no therapeutic role in methanol poisoning, which involves a different toxicological mechanism.
Question 90: Interstitial nephritis is associated with all of the following medications except:
- A. INH (Correct Answer)
- B. Diuretics
- C. Allopurinol
- D. Beta-lactam antibiotics
Explanation: ***INH*** - **Isoniazid (INH)** is primarily associated with **hepatotoxicity** (liver damage) and **peripheral neuropathy**, not typically interstitial nephritis. - While many drugs can rarely cause various adverse effects, INH is not a recognized common cause of **drug-induced interstitial nephritis**. *Beta-lactam antibiotics* - **Beta-lactam antibiotics**, including penicillins and cephalosporins, are among the most common causes of **drug-induced acute interstitial nephritis (AIN)**. - AIN is an **allergic hypersensitivity reaction** characterized by inflammation of the kidney's tubules and interstitium. *Diuretics* - Certain **diuretics**, particularly **thiazide diuretics** and **loop diuretics**, have been implicated in causing **acute interstitial nephritis**. - The mechanism is thought to be an **allergic or hypersensitivity reaction** within the renal tubules and interstitium. *Allopurinol* - **Allopurinol**, used to treat gout and hyperuricemia, is a known cause of **drug-induced acute interstitial nephritis**. - Renal involvement with allopurinol can range from mild tubular dysfunction to severe **acute kidney injury** due to AIN.