Leukotrienes are lipid mediators derived from arachidonic acid that play central roles in inflammation, bronchoconstriction, and allergic responses. For B. Pharm students, understanding leukotriene biosynthesis (PLA2, 5‑LOX, FLAP), metabolism (LTA4, LTC4, LTD4, LTE4), receptors (cysLT1, cysLT2, BLT1) and pharmacology is essential for rational drug use and development. Key therapeutic agents include leukotriene receptor antagonists (montelukast, zafirlukast) and 5‑lipoxygenase inhibitors (zileuton), each with distinct pharmacokinetics, interactions and adverse effects. Clinical relevance spans asthma, allergic rhinitis and aspirin‑exacerbated respiratory disease. This focused MCQ set emphasizes mechanisms, drug action, toxicity, and therapeutic applications to strengthen exam readiness and clinical insight. Now let’s test your knowledge with 30 MCQs on this topic.
Q1. Which enzyme catalyzes the first committed step in leukotriene biosynthesis from arachidonic acid?
- Cyclooxygenase-2 (COX-2)
- 5-Lipoxygenase (5-LOX)
- Phospholipase A2 (PLA2)
- LTA4 hydrolase
Correct Answer: 5-Lipoxygenase (5-LOX)
Q2. The immediate product formed by 5-LOX action on arachidonic acid is:
- Prostaglandin H2 (PGH2)
- Leukotriene B4 (LTB4)
- 5-Hydroperoxyeicosatetraenoic acid (5-HPETE) / LTA4
- Thromboxane A2 (TXA2)
Correct Answer: 5-Hydroperoxyeicosatetraenoic acid (5-HPETE) / LTA4
Q3. Conversion of LTA4 to LTC4 requires which cofactor or substrate?
- Glutathione (GSH)
- NADPH
- ATP
- Acetyl-CoA
Correct Answer: Glutathione (GSH)
Q4. Which leukotriene primarily mediates neutrophil chemotaxis and activation?
- LTC4
- LTD4
- LTE4
- LTB4
Correct Answer: LTB4
Q5. Cysteinyl leukotriene receptor most closely associated with bronchoconstriction in asthma is:
- BLT1
- cysLT1
- cysLT2
- BLT2
Correct Answer: cysLT1
Q6. Montelukast acts primarily by which mechanism?
- 5-LOX enzyme inhibition
- Cyclooxygenase inhibition
- Competitive antagonism at cysLT1 receptors
- Inhibition of LTA4 hydrolase
Correct Answer: Competitive antagonism at cysLT1 receptors
Q7. Zileuton’s major clinical concern relates to which adverse effect?
- Nephrotoxicity
- Hepatotoxicity
- QT prolongation
- Bone marrow suppression
Correct Answer: Hepatotoxicity
Q8. Which protein is essential as an accessory factor for 5-LOX activity and leukotriene synthesis?
- FLAP (5-LOX activating protein)
- COX-1
- mPGES-1
- Phospholipase C
Correct Answer: FLAP (5-LOX activating protein)
Q9. Which product is the terminal metabolite commonly measured in urine to assess systemic cysteinyl leukotriene production?
- Urinary LTE4
- Urinary PGE2
- Plasma LTB4
- Urinary thromboxane B2
Correct Answer: Urinary LTE4
Q10. LTA4 hydrolase converts LTA4 to:
- LTC4
- LTD4
- LTB4
- LTE4
Correct Answer: LTB4
Q11. Which leukotriene receptor antagonists are primarily metabolized by CYP enzymes and may show drug interactions?
- Zileuton only
- Montelukast and zafirlukast
- Prednisone
- Salbutamol
Correct Answer: Montelukast and zafirlukast
Q12. Aspirin-exacerbated respiratory disease (AERD) involves heightened production of:
- Prostaglandin E2
- Thromboxane A2
- Cysteinyl leukotrienes
- Endothelin
Correct Answer: Cysteinyl leukotrienes
Q13. Which statement about cysLT2 receptor is correct?
- It has higher affinity for LTB4 than cysLT1
- It is primarily expressed in vascular endothelium and heart
- It is the main receptor blocked by montelukast
- It synthesizes LTC4 from LTA4
Correct Answer: It is primarily expressed in vascular endothelium and heart
Q14. A Drug that inhibits FLAP would most directly reduce formation of:
- Prostacyclin
- All leukotrienes
- Only LTB4
- Only LTE4
Correct Answer: All leukotrienes
Q15. Which leukotriene is formed after sequential extracellular peptidase removal of amino acids from LTC4?
- LTA4
- LTB4
- LTD4 and then LTE4
- PGE2
Correct Answer: LTD4 and then LTE4
Q16. The primary therapeutic indication for leukotriene receptor antagonists is:
- Rheumatoid arthritis
- Asthma and allergic rhinitis
- Hypertension
- Type 2 diabetes
Correct Answer: Asthma and allergic rhinitis
Q17. Which leukotriene-related drug can increase warfarin levels via CYP interactions (clinically relevant)?
- Zileuton
- Montelukast
- Leukotriene B4 receptor antagonists (experimental)
- Ketorolac
Correct Answer: Zileuton
Q18. Which cellular enzyme releases arachidonic acid from membrane phospholipids, providing substrate for leukotriene synthesis?
- Phospholipase A2 (PLA2)
- 5-lipoxygenase (5-LOX)
- Cyclooxygenase (COX)
- Monoamine oxidase (MAO)
Correct Answer: Phospholipase A2 (PLA2)
Q19. Which leukotriene is least potent at causing bronchoconstriction?
- LTC4
- LTD4
- LTE4
- LTB4
Correct Answer: LTB4
Q20. Inhibition of leukotriene synthesis would be expected to reduce which of the following inflammatory features?
- Neutrophil chemotaxis mediated by LTB4
- Platelet aggregation via thromboxane
- COX-mediated prostaglandin production
- Histamine release from mast cells directly
Correct Answer: Neutrophil chemotaxis mediated by LTB4
Q21. Zafirlukast is known to inhibit which cytochrome P450 enzyme, causing interactions?
- CYP3A4 and CYP2C9
- CYP2D6 only
- CYP1A2 only
- No CYP interactions
Correct Answer: CYP3A4 and CYP2C9
Q22. Which experimental measurement best indicates increased LTB4-mediated activity in a tissue?
- Elevated urinary LTE4
- Increased neutrophil infiltration and chemotaxis assays
- Raised serum PGE2
- Decreased mast cell numbers
Correct Answer: Increased neutrophil infiltration and chemotaxis assays
Q23. Which clinical scenario suggests benefit from adding a leukotriene modifier to inhaled corticosteroids?
- Exercise-induced bronchospasm or aspirin-sensitive asthma with persistent symptoms
- Stable COPD with emphysema only
- Acute bacterial pneumonia
- Uncontrolled hypertension
Correct Answer: Exercise-induced bronchospasm or aspirin-sensitive asthma with persistent symptoms
Q24. Which leukotriene receptor subtype mediates most vascular permeability effects of cysteinyl leukotrienes?
- BLT1
- cysLT1
- cysLT2
- TP receptor
Correct Answer: cysLT1
Q25. Pharmacokinetic property: montelukast has highest oral bioavailability when taken:
- With a high-fat meal only
- On empty stomach to avoid CYP induction
- Orally with or without food; it is well absorbed and highly protein bound
- Only via intravenous infusion
Correct Answer: Orally with or without food; it is well absorbed and highly protein bound
Q26. Which gene-related variation is most likely to affect leukotriene pathway and response to therapy?
- Mutations in COX-2 gene only
- Polymorphisms in ALOX5 (5-LOX) promoter or LTC4 synthase genes
- BRCA1 mutations
- Polymorphisms in insulin receptor gene
Correct Answer: Polymorphisms in ALOX5 (5-LOX) promoter or LTC4 synthase genes
Q27. Which of the following best describes LTE4 compared to LTC4/LTD4?
- LTE4 is the precursor molecule formed first
- LTE4 is more rapidly metabolized and is a stable urinary marker
- LTE4 is the most potent bronchoconstrictor of the three
- LTE4 directly activates BLT receptors
Correct Answer: LTE4 is more rapidly metabolized and is a stable urinary marker
Q28. Which feature differentiates BLT1 from BLT2 receptors?
- BLT1 has high affinity for LTB4 and is expressed on leukocytes
- BLT1 binds cysteinyl leukotrienes preferentially
- BLT2 is the dominant receptor in bronchial smooth muscle causing constriction
- BLT1 synthesizes LTB4 from LTA4
Correct Answer: BLT1 has high affinity for LTB4 and is expressed on leukocytes
Q29. A patient on chronic zileuton therapy should have which laboratory parameter monitored regularly?
- Serum creatinine
- Liver function tests (ALT, AST)
- Complete blood count weekly
- Fasting blood glucose
Correct Answer: Liver function tests (ALT, AST)
Q30. Which strategy would most directly reduce cysteinyl leukotriene–induced bronchospasm pharmacologically?
- Administer a beta-blocker to the patient
- Use a cysLT1 receptor antagonist like montelukast
- Give a COX inhibitor such as aspirin
- Provide H2 receptor antagonists
Correct Answer: Use a cysLT1 receptor antagonist like montelukast
I am a Registered Pharmacist under the Pharmacy Act, 1948, and the founder of PharmacyFreak.com. I hold a Bachelor of Pharmacy degree from Rungta College of Pharmaceutical Science and Research. With a strong academic foundation and practical knowledge, I am committed to providing accurate, easy-to-understand content to support pharmacy students and professionals. My aim is to make complex pharmaceutical concepts accessible and useful for real-world application.
Mail- Sachin@pharmacyfreak.com