Leukotriene Modifiers — MCQs
Which drug is known to inhibit both cyclooxygenase and lipoxygenase enzymes?
All of the following are products of the cyclooxygenase pathway from arachidonic acid, except for:
What is an atypical side effect of montelukast?
Which of the following antimicrobials should not be given to a chronic asthmatic patient managed on theophylline therapy?
Match the following drugs in Column A with their contraindications in Column B. | Column A | Column B | | :-- | :-- | | 1. Morphine | 1. QT prolongation | | 2. Amiodarone | 2. Thromboembolism | | 3. Vigabatrin | 3. Pregnancy | | 4. Estrogen preparations | 4. Head injury |
Anti-inflammatory action of steroids is due to
Aspirin sensitive asthma is associated with:
A patient comes with a history of asthma and sinusitis. On looking into his medical records, you notice this has been attributed to Samter’s triad. Which drug should be avoided in this patient due to its potential to exacerbate respiratory symptoms?
Zileuton is:-
Vitamin K is involved in the post-translational modification of which amino acid?
Leukotriene Modifiers Indian Medical PG Practice Questions and MCQs
Question 1: Which drug is known to inhibit both cyclooxygenase and lipoxygenase enzymes?
- A. Aspirin
- B. Indomethacin
- C. BW755 (Correct Answer)
- D. Zileuton
Explanation: ***BW755*** - **BW755** is an experimental drug that has been shown to inhibit both the **cyclooxygenase (COX)** and **lipoxygenase (LOX)** pathways. - This dual inhibition prevents the synthesis of both **prostaglandins** and **leukotrienes**, offering a broader anti-inflammatory effect. - Due to dual pathway inhibition, it has theoretical advantages over conventional NSAIDs but is not in clinical use. *Aspirin* - **Aspirin** primarily inhibits **cyclooxygenase (COX) enzymes**, leading to reduced production of **prostaglandins** and **thromboxanes**. - It does not significantly inhibit **lipoxygenase (LOX)** enzymes. - Irreversibly acetylates COX-1 and COX-2. *Indomethacin* - **Indomethacin** is a potent **non-selective COX inhibitor**, reducing the synthesis of **prostaglandins**. - Similar to aspirin, it does not exert significant inhibitory effects on the **lipoxygenase** pathway. - One of the most potent NSAIDs available. *Zileuton* - **Zileuton** is a selective **5-lipoxygenase (5-LOX) inhibitor** used in the management of **asthma**. - It reduces the synthesis of **leukotrienes** (LTC4, LTD4, LTE4) which are mediators of bronchoconstriction and inflammation. - It does **not** inhibit cyclooxygenase enzymes, making it distinct from NSAIDs.
Question 2: All of the following are products of the cyclooxygenase pathway from arachidonic acid, except for:
- A. PGE2
- B. PGD2
- C. PGF2α
- D. LTD4 (Correct Answer)
Explanation: ***LTD4*** - Leukotriene D4 (**LTD4**) is a product of the **lipoxygenase pathway**, not the cyclooxygenase pathway, from arachidonic acid. - It plays a significant role in **bronchoconstriction** and inflammation, especially in asthma. *PGE2* - **Prostaglandin E2 (PGE2)** is a major product of the **cyclooxygenase (COX) pathway**. - It is involved in mediating **fever**, pain, and inflammation. *PGD2* - **Prostaglandin D2 (PGD2)** is also produced via the **cyclooxygenase (COX) pathway**. - It is primarily associated with allergic reactions, **bronchoconstriction**, and sleep regulation. *PGF2α* - **Prostaglandin F2 alpha (PGF2α)** is a product derived from arachidonic acid through the **cyclooxygenase (COX) pathway**. - It plays a role in **uterine contractions**, fertility, and vascular tone.
Question 3: What is an atypical side effect of montelukast?
- A. Goodpasture syndrome
- B. Membranous glomerulonephritis
- C. Bronchial asthma
- D. Churg-Strauss syndrome (Correct Answer)
Explanation: ***Churg-Strauss syndrome*** - The apparent development of **Churg-Strauss syndrome** (eosinophilic granulomatosis with polyangiitis) has been reported in patients treated with montelukast, although it is believed to be related more to the unmasking of the disease rather than a direct drug effect. - This typically occurs when **corticosteroids** are tapered or withdrawn as montelukast takes over, revealing the underlying vasculitis. *Goodpasture syndrome* - **Goodpasture syndrome** is an autoimmune disease causing rapidly progressive glomerulonephritis and pulmonary hemorrhage, characterized by anti-glomerular basement membrane (GBM) antibodies. - There is no established association between montelukast use and the development of Goodpasture syndrome. *Membranous glomerulonephritis* - **Membranous glomerulonephritis** is a common cause of nephrotic syndrome, characterized by immune complex deposition on the glomerular basement membrane. - This condition is not typically linked to the use of montelukast. *Bronchial asthma* - **Bronchial asthma** is the condition montelukast is used to treat, acting as a leukotriene receptor antagonist to reduce inflammation and bronchoconstriction. - It is a primary indication for the drug, not a side effect.
Question 4: Which of the following antimicrobials should not be given to a chronic asthmatic patient managed on theophylline therapy?
- A. Amoxicillin
- B. Cefotaxime
- C. Erythromycin (Correct Answer)
- D. Cotrimoxazole
Explanation: ***Erythromycin*** - **Erythromycin**, a macrolide antibiotic, is a potent inhibitor of the **cytochrome P450 (CYP450) enzyme system**, specifically **CYP1A2**, which is the primary enzyme responsible for theophylline metabolism. - Co-administration of erythromycin can significantly **increase theophylline levels**, leading to toxicity such as **nausea, vomiting, seizures, or cardiac arrhythmias.** - This interaction is clinically significant and erythromycin should be avoided in patients on theophylline therapy. *Amoxicillin* - **Amoxicillin** is a penicillin-class antibiotic that has minimal interaction with theophylline metabolism. - It does not significantly inhibit the **CYP1A2 enzyme** and is generally considered safe to use with theophylline. *Cefotaxime* - **Cefotaxime**, a third-generation cephalosporin, does not significantly affect the metabolism of theophylline. - It does not inhibit **CYP1A2 enzymes** and is safe for use in patients on theophylline therapy. *Cotrimoxazole* - **Cotrimoxazole** (trimethoprim/sulfamethoxazole) may slightly increase theophylline levels by inhibiting some CYP450 isoenzymes, but its effect is generally less pronounced than that of erythromycin. - While caution and monitoring are advised, it is not as strongly contraindicated as erythromycin due to a lower risk of significant toxicity in most cases.
Question 5: Match the following drugs in Column A with their contraindications in Column B. | Column A | Column B | | :-- | :-- | | 1. Morphine | 1. QT prolongation | | 2. Amiodarone | 2. Thromboembolism | | 3. Vigabatrin | 3. Pregnancy | | 4. Estrogen preparations | 4. Head injury |
- A. A-1, B-3, C-2, D-4
- B. A-4, B-1, C-3, D-2 (Correct Answer)
- C. A-3, B-2, C-4, D-1
- D. A-2, B-4, C-1, D-3
Explanation: ***A-4, B-1, C-3, D-2*** - **Morphine** is contraindicated in **head injury** as it can increase intracranial pressure and mask neurological symptoms. - **Amiodarone** is contraindicated in patients with **QT prolongation** due to its risk of inducing more severe arrhythmias like Torsades de Pointes. - **Vigabatrin** is contraindicated during **pregnancy** due to its potential for teratogenicity and adverse effects on fetal development. - **Estrogen preparations** are contraindicated in patients with a history of **thromboembolism** due to their increased risk of blood clot formation. *A-1, B-3, C-2, D-4* - This option incorrectly matches **Morphine** with QT prolongation and **Estrogen preparations** with head injury, which are not their primary contraindications. - It also incorrectly links **Vigabatrin** with thromboembolism and **Amiodarone** with pregnancy. *A-3, B-2, C-4, D-1* - This choice incorrectly associates **Morphine** with pregnancy and **Vigabatrin** with head injury, which are not the most critical or direct contraindications. - It also misaligns **Amiodarone** with thromboembolism and **Estrogen preparations** with QT prolongation. *A-2, B-4, C-1, D-3* - This option incorrectly matches **Morphine** with thromboembolism and **Amiodarone** with head injury, which are not their most significant contraindications. - It also incorrectly links **Vigabatrin** with QT prolongation and **Estrogen preparations** with pregnancy.
Question 6: Anti-inflammatory action of steroids is due to
- A. Inhibition of lipoxygenase
- B. Inhibition of phospholipase A2 (Correct Answer)
- C. Inhibition of cyclooxygenase
- D. Increased activity of lipoprotein lipase
Explanation: ***Inhibition of phospholipase A2*** - Steroids exert their potent anti-inflammatory effects primarily by inducing the synthesis of **lipocortin-1 (annexin-1)**, which then inhibits **phospholipase A2 (PLA2)** activity. - This inhibition of PLA2 prevents the release of **arachidonic acid** from cell membrane phospholipids, thereby blocking the entire cascade of downstream inflammatory mediators, including prostaglandins, thromboxanes, and leukotrienes. *Inhibition of lipoxygenase* - While leukotrienes (products of the lipoxygenase pathway) are inflammatory mediators, steroids achieve their effect upstream by blocking the precursor (arachidonic acid) rather than directly inhibiting **lipoxygenase**. - **Zileuton** is an example of a drug that directly inhibits lipoxygenase. *Inhibition of cyclooxygenase* - Steroids do not directly inhibit **cyclooxygenase (COX) enzymes**; this is the primary mechanism of action for **NSAIDs (Nonsteroidal Anti-inflammatory Drugs)** like ibuprofen and aspirin. - By inhibiting COX, NSAIDs primarily block the synthesis of prostaglandins and thromboxanes, but not leukotrienes. *Increased activity of lipoprotein lipase* - Increased activity of **lipoprotein lipase (LPL)** by steroids is related to their metabolic effects, such as promoting fat deposition and contributing to steroid-induced dyslipidemia, rather than their anti-inflammatory action. - LPL's role is in the metabolism of triglycerides in lipoproteins, which is distinct from the inflammatory cascade.
Question 7: Aspirin sensitive asthma is associated with:
- A. Extrinsic asthma
- B. Associated with nasal polyp (Correct Answer)
- C. Obesity
- D. Usually associated with urticaria
Explanation: **Associated with nasal polyp** - **Aspirin-exacerbated respiratory disease (AERD)**, also known as aspirin-sensitive asthma, is characterized by a triad of **asthma**, **rhinosinusitis with nasal polyposis**, and respiratory reactions to **aspirin** and other NSAIDs [1]. - The presence of **nasal polyps** is a key clinical feature differentiating AERD from other forms of asthma [1]. *Obesity* - While **obesity** can exacerbate asthma severity, it is not specifically associated with the pathogenesis or diagnosis of **aspirin-sensitive asthma**. - It is a general risk factor for various health issues, including more severe asthma, but lacks specificity for AERD. *Extrinsic asthma* - **Extrinsic asthma** (allergic asthma) is typically triggered by environmental allergens and involves an **IgE-mediated response** [2]. - AERD is considered a **non-allergic** or **intrinsic asthma** phenotype, as it is not triggered by traditional allergens but by pharmacologic agents [1]. *Usually associated with urticaria* - **Urticaria** (hives) can be a feature of aspirin and NSAID sensitivity, particularly in some forms of **NSAID-induced urticaria/angioedema**. - However, the classic respiratory reactions of **aspirin-sensitive asthma** (bronchospasm, rhinitis) are distinct from urticarial reactions and typically do not present with primary urticaria.
Question 8: A patient comes with a history of asthma and sinusitis. On looking into his medical records, you notice this has been attributed to Samter’s triad. Which drug should be avoided in this patient due to its potential to exacerbate respiratory symptoms?
- A. Cotrimoxazole
- B. Co-amoxiclav
- C. Chloramphenicol
- D. Aspirin (Correct Answer)
Explanation: ***Aspirin (Correct Answer)*** - Samter's triad, or **aspirin-exacerbated respiratory disease (AERD)**, is characterized by **asthma**, **nasal polyps with chronic rhinosinusitis**, and a severe reaction to **aspirin** and other **NSAIDs**. - **Aspirin** inhibits COX-1, leading to an overproduction of **leukotrienes**, which causes bronchoconstriction and exacerbates respiratory symptoms in susceptible individuals. - This is the drug that **must be avoided** in patients with Samter's triad. *Cotrimoxazole (Incorrect)* - **Cotrimoxazole** (trimethoprim-sulfamethoxazole) is an antibiotic not directly involved in the cyclooxygenase pathway. - While allergic reactions can occur, it is **not specifically contraindicated** in Samter's triad. *Co-amoxiclav (Incorrect)* - **Co-amoxiclav** (amoxicillin/clavulanic acid) is a penicillin-class antibiotic, and its mechanism of action does not involve prostaglandin synthesis. - It does not pose a specific risk for exacerbating respiratory symptoms in patients with **Samter's triad**. *Chloramphenicol (Incorrect)* - **Chloramphenicol** is an antibiotic that inhibits bacterial protein synthesis and is not associated with the pathogenesis of Samter's triad. - It does not impact the **cyclooxygenase or lipoxygenase pathways** that are central to AERD.
Question 9: Zileuton is:-
- A. Phospholipase inhibitor
- B. Leukotriene receptor antagonist
- C. 5-Lipoxygenase inhibitor (Correct Answer)
- D. Cyclooxygenase inhibitor
Explanation: ***5-Lipoxygenase inhibitor*** - **Zileuton** specifically inhibits **5-lipoxygenase**, an enzyme crucial for the synthesis of **leukotrienes**. - By blocking this enzyme, zileuton reduces the production of **pro-inflammatory leukotrienes**, which are involved in the pathophysiology of **asthma**. *Phospholipase inhibitor* - **Phospholipase A2 inhibitors** like **corticosteroids** act upstream by preventing the release of **arachidonic acid**, a precursor to both prostaglandins and leukotrienes. - Zileuton's action is more specific to the **leukotriene pathway**, occurring after arachidonic acid is already formed. *Cyclooxygenase inhibitor* - **Cyclooxygenase (COX) inhibitors** (like NSAIDs) block the synthesis of **prostaglandins** and **thromboxanes** from arachidonic acid. - Zileuton does not affect the COX pathway but rather targets the **lipoxygenase pathway**. *Leukotriene receptor antagonist* - **Leukotriene receptor antagonists** (e.g., Montelukast, Zafirlukast) block the binding of leukotrienes to their receptors, preventing their downstream effects. - While both target the **leukotriene pathway**, zileuton works by **inhibiting their production**, not their receptor binding.
Question 10: Vitamin K is involved in the post-translational modification of which amino acid?
- A. Glutamate (Correct Answer)
- B. Aspartate
- C. Glycine
- D. GABA
Explanation: **Explanation:** **1. Why Glutamate is Correct:** Vitamin K acts as a vital cofactor for the enzyme **gamma-glutamyl carboxylase**. This enzyme is responsible for the post-translational modification of specific **glutamate (Glu)** residues on certain proteins, converting them into **gamma-carboxyglutamate (Gla)** residues. This carboxylation adds a second negative charge to the glutamate side chain, which is essential for the protein's ability to bind **calcium ions (Ca²⁺)**. In the context of coagulation, this calcium binding allows clotting factors to anchor to phospholipid membranes, a critical step in the coagulation cascade. **2. Why Other Options are Incorrect:** * **Aspartate:** While chemically similar to glutamate, aspartate is not a substrate for Vitamin K-dependent carboxylation. * **Glycine:** This is the simplest amino acid and lacks the carboxyl side chain required for this specific modification. * **GABA (Gamma-Aminobutyric Acid):** GABA is an inhibitory neurotransmitter derived from glutamate via decarboxylation, not a target for Vitamin K-mediated post-translational modification. **3. High-Yield Clinical Pearls for NEET-PG:** * **Vitamin K-Dependent Factors:** Factors **II, VII, IX, X**, and anticoagulant proteins **C and S**. * **Mechanism of Warfarin:** Warfarin inhibits **Vitamin K Epoxide Reductase (VKOR)**, preventing the recycling of Vitamin K and thus inhibiting the gamma-carboxylation of glutamate residues. * **Osteocalcin:** Beyond clotting, Vitamin K is also required for the carboxylation of osteocalcin in bones, which is necessary for bone mineralization. * **Laboratory Marker:** Deficiency or Warfarin use leads to the production of **PIVKA** (Proteins Induced by Vitamin K Absence/Antagonism), which are functionally inactive factors.
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