Cysteinyl leukotrienes are produced from arachidonic acid via which enzymatic pathway?
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Clinical Pharmacology · Respiratory Medications
Leukotriene Modifiers
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In 30 seconds
Leukotriene modifiers are oral controller drugs — montelukast, zafirlukast, and zileuton — that block a chemical pathway driving airway narrowing, mucus buildup, and inflammation. They are less effective than inhaled corticosteroids but appeal because they come as pills, helping children and anyone who struggles with inhaler technique. They also cover niches ICS alone doesn't: allergic rhinitis overlap, exercise-induced bronchoconstriction, and aspirin-exacerbated respiratory disease. They are controllers, never rescue drugs, and carry real safety caveats, most notably montelukast's boxed warning for neuropsychiatric effects.
The college version
Where Leukotrienes Come From and What They Do
When airway mast cells and eosinophils are triggered by an allergen or irritant, membrane phospholipids release arachidonic acid, which is metabolized down one of two branches: the cyclooxygenase (COX) pathway, making prostaglandins, or the 5-lipoxygenase (5-LOX) pathway, making leukotrienes. The cysteinyl leukotrienes (LTC4, LTD4, LTE4) act on airway smooth muscle and vasculature to cause bronchoconstriction, increase mucus secretion, raise vascular permeability (airway edema), and recruit eosinophils that sustain inflammation. This pathway is especially prominent in aspirin-exacerbated respiratory disease, where COX inhibition by aspirin or NSAIDs shunts arachidonic acid toward the leukotriene branch and provokes severe bronchospasm.
Two Ways to Interrupt the Pathway
Montelukast and zafirlukast are cysteinyl leukotriene receptor antagonists (LTRAs): they block the receptor leukotrienes would bind, so the mediators are made but can't act. Zileuton works upstream, inhibiting 5-lipoxygenase itself so cysteinyl leukotrienes are never synthesized. All three are oral, long-term controllers, not rescue therapy — none has any role during bronchospasm already in progress.
Clinical Niches
These agents are alternative, not preferred, controllers for mild persistent asthma, useful when a patient declines or cannot tolerate ICS, or as add-on therapy. Once-daily oral dosing is attractive for children and patients with poor inhaler technique or adherence. Distinct niches include exercise-induced bronchoconstriction, comorbid allergic rhinitis (montelukast carries added rhinitis labeling), and aspirin-exacerbated respiratory disease, where blunting the leukotriene surge addresses the underlying mechanism directly.
Safety Considerations
Montelukast carries a boxed warning for serious neuropsychiatric events — agitation, aggression, sleep disturbance, depression, and suicidal thinking — which can occur even without prior psychiatric history. Patients and families need explicit counseling to watch for mood or behavior change and to seek reassessment promptly if it appears. Zafirlukast and zileuton both require monitoring for hepatotoxicity given reports of elevated liver enzymes and rare serious liver injury; periodic liver function assessment is routine. Zileuton also inhibits hepatic metabolism enough to raise theophylline levels toward toxicity and to potentiate warfarin's anticoagulant effect, so both combinations demand extra vigilance. Zafirlukast's absorption is reduced when taken with food, so consistent meal timing matters. Across the class, the unifying message is that these are daily preventers, never a substitute for a rescue inhaler during symptoms.
Eli explains
The same idea, in plain words
Explain it like I’m 10
Imagine your airway is a garden hose, and leukotrienes are gremlins that squeeze the hose narrow, dump slime inside it, and call in more gremlin friends. These medicines come as pills instead of inhalers. Montelukast and zafirlukast put earmuffs on the hose so it can't hear the gremlins' orders. Zileuton stops the gremlins from being made at all. None of them work fast — you take them daily to keep gremlins away, not to fix a squeeze already happening. Montelukast has a special warning: rarely, it can make someone feel unusually upset, moody, or have bad dreams, so parents should watch for changes and tell the doctor right away.
Check yourself
2 review questions from the chapter. Try each one, then open the answer.
A teenager with exercise-induced bronchoconstriction and seasonal allergic rhinitis is embarrassed to use an inhaler at school. Why might a leukotriene modifier be considered here, and what should never be forgotten about its role?
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Oral once-daily dosing avoids the technique and social barriers of inhalers, and it targets the shared leukotriene pathway behind both problems — but it must still be used as a daily preventer, never a substitute for a rescue inhaler if an attack occurs.
Think of it like taking a daily vitamin to keep gremlins away rather than having an emergency tool for when the hose is already squeezed shut — the pill can't undo an attack in progress.
A patient started on zileuton is also taking warfarin and theophylline. What two interaction concerns should the care team monitor for, and why do they occur?
Show answer
Zileuton can raise theophylline levels toward toxicity and strengthen warfarin's blood-thinning effect, because it inhibits the liver enzymes that normally clear both drugs.
When the liver's clean-up crew is slowed down, both drugs build up higher than expected, so levels and clotting studies need closer watching whenever zileuton is added.
Quick check
3 questions here. Answers stay hidden until you check.
Which drug works by inhibiting leukotriene synthesis rather than blocking the receptor?
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Which best describes the boxed warning specific to montelukast?
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