Role of P-glycoprotein in Drug Interactions — MCQs
A patient with HIV who is currently on antiretroviral therapy consisting of zidovudine, lamivudine, and nevirapine is diagnosed with tuberculosis. Considering potential drug interactions, which of the following TB drugs should be changed in this patient?
Pharmacodynamics deals with:-
Which of the following factors acts in vesicle targeting?
Which of the following is NOT a mechanism of antibiotic resistance?
The initial origin of new drug resistance genes in bacteria most commonly occurs due to:
What is the mechanism of action of ticagrelor?
Dapsone is used for treatment of bacterial infections as well as for immunomodulatory actions. What is mechanism of dapsone for these indications?
MDR gene acts by what mechanism?
Multidrug-resistant (MDR) tuberculosis shows resistance to which of the following drugs?
Which of the following drugs has the least significant drug interaction with digoxin?
Role of P-glycoprotein in Drug Interactions Indian Medical PG Practice Questions and MCQs
Question 1: A patient with HIV who is currently on antiretroviral therapy consisting of zidovudine, lamivudine, and nevirapine is diagnosed with tuberculosis. Considering potential drug interactions, which of the following TB drugs should be changed in this patient?
- A. Isoniazid
- B. Rifampicin (Correct Answer)
- C. Ethambutol
- D. Streptomycin
- E. Pyrazinamide
Explanation: **Rifampicin** - **Rifampicin** is a potent **CYP450 enzyme inducer**, which significantly increases the metabolism of **nevirapine**, a non-nucleoside reverse transcriptase inhibitor (NNRTI), leading to subtherapeutic levels and potential treatment failure. - In patients on **nevirapine-based ART**, **rifampicin** is typically avoided or replaced with other rifamycins (like **rifabutin**), or the antiretroviral regimen is switched to one that is less affected by enzyme induction. *Isoniazid* - **Isoniazid** does not have significant, clinically problematic interactions with the antiretroviral regimen mentioned (zidovudine, lamivudine, nevirapine), and is generally well-tolerated. - It is a cornerstone of TB treatment and is usually continued without dose adjustment or substitution in this scenario. *Pyrazinamide* - **Pyrazinamide** is part of the standard first-line TB treatment regimen and does not have clinically significant drug interactions with zidovudine, lamivudine, or nevirapine. - It can be safely continued without dose adjustment in patients on this ART regimen. *Ethambutol* - **Ethambutol** primarily causes **optic neuritis** as a side effect and does not have significant pharmacokinetic interactions with the antiretroviral drugs listed. - Its use in TB treatment alongside this ART regimen is generally safe and does not require a change. *Streptomycin* - **Streptomycin** is an **aminoglycoside antibiotic** primarily used for multi-drug resistant TB or in specific situations, and its main toxicity is **ototoxicity** and **nephrotoxicity**. - It does not have known significant drug interactions with zidovudine, lamivudine, or nevirapine that would necessitate a change.
Question 2: Pharmacodynamics deals with:-
- A. Latency of onset
- B. Mechanism of action of a drug (Correct Answer)
- C. Transport of drug across the biological membranes
- D. Mode of excretion of a drug
Explanation: Detailed study of the **Mechanism of action of a drug** [1][2] - **Pharmacodynamics** describes what the **drug does to the body**, including its **molecular targets** and biochemical effects [3]. - This involves the study of the drug's mechanisms to produce its therapeutic or toxic effects [2]. *Latency of onset* - **Latency of onset** refers to the time it takes for a drug to start producing its effects, which is a pharmacokinetic rather than a pharmacodynamic parameter. - It deals with the drug's absorption and distribution rather than its interaction with the body once it reaches its site of action. *Transport of drug across the biological membranes* - The **transport of drugs across biological membranes** is a key aspect of **pharmacokinetics**, specifically absorption and distribution [1]. - This process determines how much drug reaches its target site, not how it interacts with the target. *Mode of excretion of a drug* - The **mode of excretion** of a drug (e.g., renal, hepatic) falls under **pharmacokinetics**, addressing how the body gets rid of the drug. - This process influences the drug's duration of action and elimination half-life, not its mechanism of action.
Question 3: Which of the following factors acts in vesicle targeting?
- A. Sec 12
- B. Rab (Correct Answer)
- C. Ras
- D. SNARE
Explanation: ***Rab*** - **Rab GTPases** are small G proteins that regulate many steps of membrane trafficking, including vesicle formation, cargo selection, vesicle budding, uncoating, motility, and fusion. - They act as molecular switches, cycling between an active GTP-bound state and an inactive GDP-bound state, thereby coordinating the proper targeting of vesicles to their destination membranes. *Sec 12* - **Sec12** is a **GEF (guanine nucleotide exchange factor)** for **Sar1**, which is involved in COPII vesicle formation from the ER. - While it initiates a step in vesicle budding, it does not directly act as a targeting molecule to guide the vesicle to its destination. *Ras* - **Ras GTPases** are primarily involved in cell signaling pathways regulating cell proliferation, differentiation, and survival. - They are not directly involved in the process of **vesicle targeting** in membrane trafficking. *SNARE* - **SNARE proteins** (soluble N-ethylmaleimide-sensitive factor attachment protein receptor) are crucial for the **fusion of vesicles** with their target membranes. - While essential for the later stages of trafficking, they mediate membrane fusion rather than initial vesicle targeting.
Question 4: Which of the following is NOT a mechanism of antibiotic resistance?
- A. Efflux pump activity
- B. Inactivation by enzymes such as beta-lactamase
- C. Modification of drug target sites
- D. Increased drug absorption (Correct Answer)
Explanation: ***Increased drug absorption*** - **Increased drug absorption** would lead to a higher intracellular concentration of the antibiotic, making it *more potent* against the bacteria rather than contributing to resistance. - Antibiotic resistance mechanisms aim to *reduce the effective concentration* of the drug at its target site or *alter the target itself*. *Efflux pump activity* - **Efflux pumps** are bacterial membrane proteins that actively pump antibiotics out of the bacterial cell [3]. - This mechanism *reduces the intracellular concentration* of the antibiotic, preventing it from reaching its therapeutic target [3]. *Inactivation by enzymes such as beta-lactamase* - Bacteria can produce enzymes like **beta-lactamase** that *chemically modify or degrade* the antibiotic molecule, rendering it inactive [2]. - This is a common mechanism of resistance against **beta-lactam antibiotics** (e.g., penicillin, cephalosporins) [2]. *Modification of drug target sites* - Bacteria can develop mutations that *alter the structure of the antibiotic's target site*, such as a bacterial ribosome or cell wall component [1]. - This change in the target means the antibiotic can no longer bind effectively or interfere with cellular processes, thus *losing its efficacy* [1].
Question 5: The initial origin of new drug resistance genes in bacteria most commonly occurs due to:
- A. Translation
- B. Mutation (Correct Answer)
- C. Conjugation
- D. Transduction
Explanation: ***Mutation*** - **Random genetic changes** in bacteria can alter drug targets or introduce drug-inactivating enzymes, leading to resistance. - **Spontaneous mutations** in the bacterial genome are the primary source of new resistance genes that did not previously exist in the bacterial population. - While mutations occur at low frequency, they are the fundamental mechanism by which novel resistance traits first arise. *Translation* - This is the process of synthesizing proteins from mRNA; it is a fundamental cellular process and not a cause of drug resistance. - Errors in translation are generally lethal to the cell and do not typically confer specific drug-resistant phenotypes. *Conjugation* - This is a mechanism for **horizontal gene transfer** where bacteria directly transfer genetic material, including resistance genes, via a pilus. - While conjugation is the **most important mechanism for spreading resistance** in clinical settings, it transfers pre-existing resistance genes rather than creating new ones. *Transduction* - This is another form of **horizontal gene transfer** involving bacteriophages (viruses) carrying bacterial genes, including resistance genes, between bacteria. - Similar to conjugation, transduction is a mechanism for the **transfer** of pre-existing resistance genes, not their original creation.
Question 6: What is the mechanism of action of ticagrelor?
- A. PAR1 activator
- B. P2Y12 inhibitor (Correct Answer)
- C. P2Y12 activator
- D. PAR1 inhibitor
Explanation: ***P2Y12 inhibitor*** - Ticagrelor is an **oral antiplatelet agent** that works by reversibly binding to the **P2Y12 receptor** on platelets. - This binding prevents adenosine diphosphate (ADP) from activating the P2Y12 receptor, which is crucial for **platelet aggregation** and **thrombus formation**. *PAR1 inhibitor* - **PAR1 inhibitors** (e.g., vorapaxar) block the thrombin receptor on platelets, leading to antiplatelet effects. - This mechanism is distinct from ticagrelor's action on the P2Y12 receptor. *PAR1 activator* - Activating **PAR1** would promote platelet aggregation and activation, which is the opposite effect of an antiplatelet medication like ticagrelor. - This mechanism would increase the risk of thrombosis. *P2Y12 activator* - Activating the **P2Y12 receptor** would lead to increased platelet aggregation and is not the mechanism of action for an antiplatelet drug. - Drugs that activate P2Y12 would promote the formation of blood clots.
Question 7: Dapsone is used for treatment of bacterial infections as well as for immunomodulatory actions. What is mechanism of dapsone for these indications?
- A. Inhibition of cell wall synthesis
- B. Inhibition of ergosterol in cell membranes
- C. Competition with PABA in folic acid synthesis (Correct Answer)
- D. Inhibition of protein synthesis
Explanation: ***Competition with PABA in folic acid synthesis*** - **Dapsone** is a **sulfone drug** that functions as a competitive antagonist of **para-aminobenzoic acid (PABA)**. - This competition blocks the enzyme **dihydropteroate synthase**, preventing **folic acid synthesis** in susceptible bacteria, which is essential for their growth. *Inhibition of cell wall synthesis* - This mechanism is characteristic of **beta-lactam antibiotics** (penicillins, cephalosporins) and **glycopeptides** (vancomycin), which target peptidoglycan synthesis. - **Dapsone** does not interfere with cell wall integrity or synthesis. *Inhibition of ergosterol in cell membranes* - This is the primary mechanism of action for many **antifungal drugs**, such as **azoles** (fluconazole) and **polyenes** (amphotericin B). - **Dapsone** does not target fungal cell membranes or ergosterol synthesis. *Inhibition of protein synthesis* - This mechanism is employed by various classes of **antibiotics**, including **tetracyclines**, **macrolides**, and **aminoglycosides**, which bind to bacterial ribosomes. - **Dapsone's** mechanism is distinct from inhibiting protein production.
Question 8: MDR gene acts by what mechanism?
- A. Causes efflux of drug (Correct Answer)
- B. Inhibit drug activation
- C. Inhibit intracellular DNA synthesis
- D. Inhibit DNA repair
Explanation: ***Causes efflux of drug*** - The **MDR gene** (multidrug resistance gene) encodes for **P-glycoprotein**, an ATP-dependent efflux pump. - This pump actively **transports drugs out of the cell**, reducing their intracellular concentration and effectiveness. *Inhibit drug activation* - This mechanism is associated with enzymes like **CYP450 isoenzymes** or **esterases** that metabolize prodrugs into their active forms. - The MDR gene and its product, P-glycoprotein, are efflux pumps and do not directly inhibit drug activation. *Inhibit intracellular DNA synthesis* - This is the mechanism of action for certain classes of drugs, such as **antimetabolites** (e.g., methotrexate) or **nucleoside analogs**. - The MDR gene's role is in drug transport, not in interfering with DNA synthesis itself. *Inhibit DNA repair* - Some chemotherapeutic agents, like **PARP inhibitors**, work by preventing cells from repairing DNA damage, leading to apoptosis. - While related to drug action, this is not the primary mechanism by which the MDR gene confers resistance; instead, it reduces drug exposure to DNA targets.
Question 9: Multidrug-resistant (MDR) tuberculosis shows resistance to which of the following drugs?
- A. Isoniazid, rifampicin, and fluoroquinolone
- B. Fluoroquinolone
- C. Isoniazid, rifampicin, and kanamycin
- D. Isoniazid and rifampicin only (Correct Answer)
Explanation: ***Isoniazid and rifampicin only*** - **Multidrug-resistant (MDR) tuberculosis** is specifically defined by resistance to both **isoniazid** and **rifampicin**. - These two drugs are considered the most effective first-line anti-TB medications, making resistance to both a significant treatment challenge. *Isoniazid, rifampicin, and fluoroquinolone* - Resistance to **isoniazid**, **rifampicin**, and *any* fluoroquinolone defines **pre-extensively drug-resistant (pre-XDR) TB**, not MDR-TB. - Adding resistance to a fluoroquinolone indicates a more severe and harder-to-treat form of tuberculosis. *Fluoroquinolone* - Resistance to **fluoroquinolone** alone does not define MDR-TB; it is only one component of resistance that, when combined with resistance to isoniazid and rifampicin, signifies pre-XDR or XDR-TB. - While fluoroquinolones are important second-line drugs, their resistance in isolation does not meet the criteria for MDR-TB. *Isoniazid, rifampicin, and kanamycin* - Resistance to **isoniazid**, **rifampicin**, and *any* second-line injectable agent (like **kanamycin**, capreomycin, or amikacin) defines **extensively drug-resistant (XDR) TB**, not MDR-TB. - XDR-TB represents an even more complex and difficult form of the disease to treat, requiring highly specialized regimens.
Question 10: Which of the following drugs has the least significant drug interaction with digoxin?
- A. Cholestyramine
- B. Thiazide diuretics
- C. Quinidine
- D. Amlodipine (Correct Answer)
Explanation: ***Amlodipine*** - **Amlodipine** generally has a **minimal impact** on digoxin levels and rarely causes clinically significant interactions. - It works through a different mechanism (calcium channel blockade) and does not typically affect digoxin's absorption, distribution, metabolism, or excretion. *Cholestyramine* - **Cholestyramine** is an **ion-exchange resin** that can bind to digoxin in the gastrointestinal tract, significantly **reducing its absorption**. - This interaction can lead to **subtherapeutic digoxin levels** and reduced therapeutic efficacy. *Thiazide diuretics* - **Thiazide diuretics** can cause **hypokalemia**, which significantly **potentiates digoxin toxicity**. - Low potassium levels allow more digoxin to bind to the Na+/K+-ATPase pump, increasing its inotropic and arrhythmogenic effects. *Quinidine* - **Quinidine** can **increase serum digoxin concentrations** by inhibiting its renal and non-renal clearance and displacing it from tissue binding sites. - This can lead to **digoxin toxicity**, necessitating a reduction in digoxin dosage when co-administered.
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