Generic Name

Singulair

Mechanism

Singulair (montelukast) is a selective leukotriene receptor antagonist that blocks the cysteinyl leukotriene receptor‑1 (CysLT1) on airway smooth muscle and inflammatory cells. This inhibition reduces leukotriene‑mediated bronchoconstriction, mucosal edema, mucus secretion, and eosinophil recruitment, thereby improving airway patency and reducing inflammation in allergic diseases.

Pharmacokinetics

• Absorption: Oral bioavailability ~2‑3 % (first‑pass metabolism). Peak plasma concentrations reached in 4‑6 h.
• Distribution: Widely distributed; crosses placenta and blood‑brain barrier; protein binding ~92 %.
• Metabolism: Primarily hepatic via CYP3A4/3A5 and CYP2C9, producing inactive metabolites.
• Elimination: Excreted mainly in stool (≈80 %) and urine (≈20 %).
• Half‑life: ~2–5 h; steady‑state achieved after ~5‑7 days.
• Special populations: Dose adjustments not required for mild‑moderate kidney or liver impairment; caution in severe hepatic disease.

Indications

• Asthma (maintenance therapy) – pediatric and adult populations.
• Allergic rhinitis – seasonal or perennial.
• Exercise‑induced bronchoconstriction – when patients prefer oral therapy over β₂‑agonists.

> Note: Not used for acute asthma attacks; pairs well with inhaled corticosteroids or short‑acting β₂‑agonists.

Contraindications

• Hypersensitivity to montelukast or any excipients.
• Pregnancy: Category C – use only if benefits outweigh risks.
• Concurrent high‑dose CYP3A4 inhibitors (e.g., ketoconazole) may increase plasma levels; monitor for toxicity.
• Severe hepatic impairment: may lead to accumulation of active metabolites.
• Liver disease: monitor hepatic function tests.
• Neuropsychiatric events: vigilance for mood changes, agitation, suicidal ideation, particularly in adolescents and young adults.

Dosing

• Adults & pediatrics ≥6 years: 10 mg once daily (preferred bedtime).
• Children 2–5 years: 5 mg once daily.
• Children <2 years: Not approved.
• Exercise‑induced bronchoconstriction: 10 mg orally, 2–4 h before exercise.
• Store: Oral capsules (ororally disintegrating for pediatric use) or bulk tablets; single‑dose formulation.
• Missed dose: Take as soon as remembered; skip if within 4 h of next dose.

Adverse Effects

• Common (≤10 % incidence)
• Headache, insomnia, drowsiness, back pain
• Upper respiratory infections
• Gastrointestinal upset (abdominal pain, nausea)
• Serious (≤1 % incidence)
• Severe neuropsychiatric events: aggression, depression, suicide ideation (FDA boxed warning)
• Hepatic reactions: elevated transaminases, hepatitis
• Severe hypersensitivity or anaphylaxis

> Monitoring: Counsel patients and caregivers to report mood changes; periodic liver enzymes if clinically indicated.

Monitoring

• Baseline:
• Liver function tests if history of hepatic disease.
• Neuropsychiatric baseline assessment in pediatric/young adult patients (screening questionnaire).
• Follow‑up:
• Liver enzymes every 3–6 months in patients with risk factors.
• Routine serum creatinine not required.
• Track asthma control (PEF, symptom diary) to assess efficacy.

Clinical Pearls

• Fast‑track asthma: Montelukast can be started early in children who demonstrate poor adherence to inhalers; its oral route improves compliance in school‑age kids.
• Dual therapy: Add *montelukast* to inhaled corticosteroids for patients with allergic rhinitis, reducing need for rescue β₂‑agonists.
• Dose adjustment: The 10 mg dosage is effective in adults; increasing to 20 mg above 6 years is not supported by evidence and may increase adverse events.
• Seizure prophylaxis? No; montelukast has no anticonvulsant properties—do not substitute for antiepileptics.
• Weekend dosing: Evidence suggests continuous daily use provides better control; skipping doses on weekends often reduces efficacy and increases relapse risk.

> Take‑away: Montelukast’s unique leukotriene‑blocking action makes it a valuable maintenance agent, especially in patients with coexisting allergic rhinitis or those who prefer oral therapy, but vigilance for mood changes and liver dysfunction remains essential.