Drug-Food Interactions — MCQs

10 questions

Safe injection strategy will reduce the occurrence of:

A factor that is likely to increase the duration of action of a drug that is partially metabolized by CYP3A4 in the liver is:

Which of the following medications does not interact with warfarin?

Which drug should not be given with ketoconazole?

The anticoagulant activity of warfarin can be reduced by all of the following except.

In patients taking tadalafil, the most serious drug interaction occurs with:

Which of the following DPP-IV inhibitors is safe for use in chronic kidney disease patients without requiring dose modification?

Which of the following combinations can result in severe toxicity due to inhibition of cytochrome P450 enzymes?

Which of the following statements about hypolipidemic drugs is false?

Q10

Statins act on:

Drug-Food Interactions Indian Medical PG Practice Questions and MCQs

Question 1: Safe injection strategy will reduce the occurrence of:

A. Hepatitis E
B. Hepatitis A
C. Hepatitis B (Correct Answer)
D. Typhoid

Explanation: ***Hepatitis B*** - **Hepatitis B** is a blood-borne virus commonly transmitted through contaminated needles and syringes. - Implementing **safe injection strategies**, such as using sterile equipment and proper disposal, effectively reduces its transmission. *Hepatitis E* - **Hepatitis E** is primarily transmitted via the **fecal-oral route**, often through contaminated water. - It is not typically associated with unsafe injection practices. *Hepatitis A* - **Hepatitis A** is also spread primarily through the **fecal-oral route**, often from contaminated food or water. - It has no significant link to injection safety practices. *Typhoid* - **Typhoid fever** is caused by *Salmonella Typhi* and is transmitted through the **ingestion of contaminated food or water**. - Injection practices do not play a role in its transmission.

Question 2: A factor that is likely to increase the duration of action of a drug that is partially metabolized by CYP3A4 in the liver is:

A. Chronic administration of phenobarbital with the drug
B. Displacement from tissue binding sites by another drug
C. Chronic administration of rifampicin
D. Chronic administration of cimetidine with the drug (Correct Answer)

Explanation: ***Chronic administration of cimetidine with the drug*** - **Cimetidine** is a potent inhibitor of various **cytochrome P450 (CYP450) enzymes**, including **CYP3A4**. - By inhibiting the metabolism of a drug predominantly metabolized by **CYP3A4**, cimetidine will increase its plasma concentration and extend its **duration of action**. *Chronic administration of phenobarbital with the drug* - **Phenobarbital** is a strong **inducer of CYP450 enzymes**, including **CYP3A4**. - Induction would accelerate the metabolism of the drug, thus **decreasing its duration of action**, not increasing it. *Displacement from tissue binding sites by another drug* - Displacement from tissue binding sites would primarily increase the **free fraction of the drug in the plasma**, leading to a more rapid distribution to eliminating organs and potentially **shorter duration of action** if elimination is extraction-limited. - This mechanism does not directly impact the **metabolic rate** unless clearance is significantly altered through increased availability for metabolism. *Chronic administration of rifampicin* - **Rifampicin** is a potent **inducer of CYP3A4** and other CYP enzymes. - Its administration would lead to **increased metabolism** of the co-administered drug, thereby **reducing its duration of action**.

Question 3: Which of the following medications does not interact with warfarin?

A. Barbiturate
B. Oral contraceptive
C. Cephalosporins
D. Benzodiazepines (Correct Answer)

Explanation: ***Benzodiazepines*** - **Benzodiazepines** are generally considered safe to use with warfarin as they are extensively metabolized in the liver, but they do not typically alter the **cytochrome P450 enzymes** responsible for warfarin metabolism. - They also do not interfere with **vitamin K recycling** or **platelet function**, which are key mechanisms through which other drugs interact with warfarin. *Barbiturate* - **Barbiturates** are **potent inducers of hepatic enzymes**, particularly CYP2C9, which is responsible for metabolizing warfarin. - This enzyme induction leads to **increased warfarin metabolism**, reducing its anticoagulant effect and necessitating higher warfarin doses. *Oral contraceptive* - **Oral contraceptives** can **reduce the anticoagulant effect of warfarin** by inducing clotting factors or inhibiting warfarin metabolism. - This interaction can increase the risk of **thromboembolic events** in patients on warfarin. *Cephalosporins* - Certain **cephalosporins**, especially those with a **methylthiotetrazole (MTT) side chain** (e.g., Cefamandole, Cefoperazone, Moxalactam), can **inhibit vitamin K epoxide reductase**. - This inhibition leads to a **decrease in vitamin K-dependent clotting factors**, thus potentiating the anticoagulant effect of warfarin and increasing bleeding risk.

Question 4: Which drug should not be given with ketoconazole?

A. Indinavir (Correct Answer)
B. Macrolide
C. All of the options
D. Aminoglycoside

Explanation: ***Correct: Indinavir*** - **Indinavir** is a **protease inhibitor (antiretroviral)** that is primarily metabolized by **CYP3A4** - **Ketoconazole** is a **potent CYP3A4 inhibitor** that significantly increases indinavir plasma concentrations - Co-administration leads to **increased risk of indinavir toxicity** including nephrolithiasis, hyperbilirubinemia, and hepatotoxicity - **Dose reduction of indinavir is required** if concurrent use is necessary (typically reduce to 600 mg q8h from 800 mg q8h) *Incorrect: Macrolide* - Many **macrolides** (erythromycin, clarithromycin) are CYP3A4 substrates and can interact with ketoconazole - While caution is advised due to **QT prolongation risk**, this interaction is less severe than with indinavir - Not an absolute contraindication but requires monitoring *Incorrect: Aminoglycoside* - **Aminoglycosides** (gentamicin, amikacin, tobramycin) are **NOT metabolized by CYP450 enzymes** - They are **hydrophilic** and eliminated **unchanged by renal excretion** - **No clinically significant interaction** with ketoconazole - Can be safely co-administered without dose adjustment *Key Learning Point* - Ketoconazole inhibits CYP3A4, affecting metabolism of many drugs including **protease inhibitors, calcium channel blockers, statins, and some macrolides** - Always check for CYP3A4 substrate drugs when prescribing azole antifungals

Question 5: The anticoagulant activity of warfarin can be reduced by all of the following except.

A. Aspirin (Correct Answer)
B. Rifampin
C. Vitamin K
D. Carbamazepine

Explanation: ***Aspirin*** - **Aspirin** does NOT reduce warfarin's anticoagulant activity; instead, it increases the risk of bleeding through a synergistic effect. - Aspirin inhibits platelet aggregation via **cyclooxygenase-1 (COX-1)** inhibition, preventing thromboxane A2 formation, which is a different mechanism from warfarin's inhibition of vitamin K-dependent clotting factors. - When combined with warfarin, aspirin **potentiates** the overall antithrombotic effect and increases bleeding risk. *Carbamazepine* - **Carbamazepine** is a potent inducer of hepatic cytochrome P450 enzymes (CYP2C9, CYP3A4). - By increasing warfarin metabolism, it **reduces** warfarin's plasma concentrations and decreases its anticoagulant effect. - Patients on this combination may require higher warfarin doses to maintain therapeutic INR. *Rifampin* - **Rifampin** is one of the most potent inducers of hepatic cytochrome P450 enzymes (CYP2C9, CYP3A4). - It significantly increases warfarin metabolism, leading to **reduced** plasma concentrations and diminished anticoagulant effect. - This interaction often necessitates substantial increases in warfarin dosage. *Vitamin K* - **Vitamin K** is the direct antagonist of warfarin's mechanism of action. - Warfarin inhibits vitamin K epoxide reductase, preventing the regeneration of active vitamin K needed for synthesis of clotting factors II, VII, IX, and X. - Administration of vitamin K **reverses** warfarin's anticoagulant effect by bypassing the inhibited enzyme and restoring clotting factor production.

Question 6: In patients taking tadalafil, the most serious drug interaction occurs with:

A. Alpha-Blockers
B. Ketoconazole
C. Rifampicin
D. Nitrates (Correct Answer)

Explanation: ***Nitrates*** - The co-administration of **tadalafil** (a PDE5 inhibitor) with **nitrates** can cause a dangerous and potentially fatal drop in **blood pressure**. - Both drug classes lead to increased cGMP levels, resulting in excessive **vasodilation** and profound **hypotension**. *Alpha-Blockers* - Alpha-blockers, while able to cause **hypotension** when taken with tadalafil, generally lead to less severe interactions than nitrates. - The combination requires caution and potentially dose adjustments, but typically does not result in the same life-threatening blood pressure drops as seen with nitrates. *Ketoconazole* - **Ketoconazole** is a strong **CYP3A4 inhibitor**, which can increase the plasma concentration of tadalafil. - This interaction can potentiate tadalafil's effects and increase the risk of side effects, but it doesn't create an immediate, life-threatening hypotensive crisis like nitrates. *Rifampicin* - **Rifampicin** is a potent **CYP3A4 inducer**, which can significantly decrease the plasma concentration of tadalafil. - This interaction primarily leads to a **reduced efficacy** of tadalafil, rather than a dangerous increase in adverse effects or a severe drug-drug interaction.

Question 7: Which of the following DPP-IV inhibitors is safe for use in chronic kidney disease patients without requiring dose modification?

A. Sitagliptin
B. Vildagliptin
C. Linagliptin (Correct Answer)
D. Saxagliptin

Explanation: ***Linagliptin*** - Unlike other **DPP-IV inhibitors**, **linagliptin** is primarily eliminated via **biliary/fecal excretion** (~85%) rather than renal excretion. - This unique elimination pathway makes it **safe** for use in patients with **chronic kidney disease** at its usual dose, without the need for dose adjustment. - It is the **only DPP-IV inhibitor** that does not require dose modification in CKD. *Sitagliptin* - **Sitagliptin** is primarily eliminated by the **kidneys** (~80% renal excretion), requiring **significant dose adjustments** in patients with **renal impairment**. - Without dose modification, there is an increased risk of **drug accumulation** and adverse effects in CKD patients. *Vildagliptin* - **Vildagliptin** undergoes **hydrolysis** with subsequent **renal excretion** of inactive metabolites, requiring **dose reduction** in patients with moderate to severe **renal impairment**. - Not recommended in severe renal impairment (eGFR <50 mL/min). *Saxagliptin* - **Saxagliptin** is partially eliminated via **renal excretion** and requires **dose reduction** by 50% in patients with moderate to severe **CKD**. - Both parent drug and active metabolite accumulate in renal impairment, necessitating dose adjustment.

Question 8: Which of the following combinations can result in severe toxicity due to inhibition of cytochrome P450 enzymes?

A. Amiodarone + Atorvastatin
B. Carbamazepine + Atorvastatin
C. Atorvastatin + Itraconazole (Correct Answer)
D. Phenytoin + Atorvastatin

Explanation: ***Atorvastatin + Itraconazole*** - **Itraconazole** is a potent inhibitor of **CYP3A4**, the primary enzyme responsible for atorvastatin's metabolism. - Co-administration leads to significantly increased **atorvastatin plasma concentrations**, raising the risk of severe side effects like **rhabdomyolysis** and **hepatotoxicity**. *Amiodarone + Atorvastatin* - **Amiodarone** is a moderate **CYP3A4 inhibitor** and can increase atorvastatin levels, but the inhibition is **less potent** than itraconazole. - While this combination does carry a risk and requires dose adjustment, the interaction is **less severe** compared to the potent inhibition seen with itraconazole. - The direct CYP inhibition leading to severe atorvastatin toxicity is less pronounced than with itraconazole. *Carbamazepine + Atorvastatin* - **Carbamazepine** is a potent **CYP3A4 inducer**, meaning it would increase the metabolism of atorvastatin, potentially *decreasing* its efficacy rather than causing toxicity through inhibition. - This interaction would typically lead to subtherapeutic atorvastatin levels, rather than severe toxicity. *Phenytoin + Atorvastatin* - **Phenytoin** is also a potent **CYP3A4 inducer**, similar to carbamazepine. - Concurrent use would likely lead to enhanced metabolism and **reduced efficacy of atorvastatin**, not increased toxicity due to enzyme inhibition.

Question 9: Which of the following statements about hypolipidemic drugs is false?

A. Gemfibrozil causes myopathy
B. Gemfibrozil can increase myopathy caused by statins
C. Lovastatin can cause hepatic dysfunction
D. Cholesterol reducing drugs are contraindicated in child less than 8 years (Correct Answer)

Explanation: ***Cholesterol reducing drugs are contraindicated in child less than 8 years*** - While cholesterol-lowering drugs are generally avoided in young children, there are specific **genetic dyslipidemias** where treatment may be initiated earlier under specialist supervision [1]. - The statement is **false** because some genetic conditions may necessitate earlier treatment, making a blanket contraindication for all children under 8 inaccurate [1]. *Gemfibrozil causes myopathy* - **Gemfibrozil** (a fibric acid derivative) can indeed cause **myopathy**, especially when used alone or in combination with other lipid-lowering agents [2]. - This adverse effect is thought to be due to its mechanism of action affecting fatty acid metabolism and muscle integrity. *Gemfibrozil can increase myopathy caused by statins* - The co-administration of **gemfibrozil** with **statins** significantly increases the risk of **myopathy** and **rhabdomyolysis** [2]. - This is primarily due to gemfibrozil inhibiting the **glucuronidation** of statins, which increases statin plasma concentrations [2]. *Lovastatin can cause hepatic dysfunction* - **Statins**, including **lovastatin**, can cause **elevations in liver transaminases** and, in rare cases, lead to **drug-induced liver injury** [1]. - Regular monitoring of liver function tests is recommended when initiating statin therapy and during follow-up [2].

Question 10: Statins act on:

A. HMG CoA synthetase
B. HMG CoA reductase (Correct Answer)
C. HMG CoA hydratase
D. Squalene epoxidase

Explanation: ***HMG CoA reductase*** - **HMG-CoA reductase inhibitors** (statins) are the most effective and widely used class of hypolipidemic agents [1, 2, 3]. - This enzyme is the **rate-limiting step** in cholesterol biosynthesis in the liver [1, 2, 3]. *HMG CoA synthetase* - HMG-CoA synthetase is involved in the synthesis of **HMG-CoA** from acetyl-CoA and acetoacetyl-CoA. - This enzyme precedes the HMG-CoA reductase step and is **not the primary target** for cholesterol-lowering drugs. *Squalene epoxidase* - Squalene epoxidase is an enzyme involved in the later stages of the **cholesterol synthesis pathway**, specifically in converting squalene to squalene epoxide. - While inhibition of this enzyme would reduce cholesterol synthesis, it is **not the main target** of current widely used hypolipidemic agents. *HMG CoA hydratase* - HMG-CoA hydratase (also known as HMG-CoA lyase) is involved in the breakdown of HMG-CoA into **acetyl-CoA and acetoacetate** in ketogenesis. - It is **not directly involved** in the main pathway of cholesterol synthesis that is targeted by current hypolipidemic drugs.

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