Montelukast Sodium
Cyclopropaneacetic acid derivative leukotriene inhibitor
Also known as: Singulair · MK-476 · L-706631 · montelukastum
Reviewed by the VetSheet Veterinary TeamUpdated Apr 5, 2026Evidence-based veterinary reference
Doses are a clinical reference for licensed veterinary professionals. Always confirm against the current label and the individual patient.
Dosing by species
🌎 NA — North America🌍 EU — Europe
Cats
| Indication | Dose | Route | Frequency | Duration | Region |
|---|---|---|---|---|---|
| Feline asthma | 0.5-1 mg/kg PO once daily (q24h) | PO | q24h | — | 🌎 NA |
| Adjunctive treatment of the chronic 'snuffler' | 0.25-0.5 mg/kg PO q24h | PO | q24h | — | 🌎 NA |
| Inflammatory Bowel Disease (IBD) | 0.5-1 mg/kg PO once daily | PO | q24h | — | 🌎 NA |
| Adjunctive treatment of feline heartworm | 2 mg total dose (PO) once daily | PO | q24h | — | 🌎 NA |
- Feline asthma: Anecdotal reports of efficacy; more conclusive evidence is needed before regular use.
- Adjunctive treatment of the chronic 'snuffler': i.e., 1/8th of a 10 mg Singulair tablet.
- Inflammatory Bowel Disease (IBD): For mild cases involving eosinophils and lymphocytes. May be used in combination with other drugs.
- Adjunctive treatment of feline heartworm: Anecdotal evidence suggests it may help thwart acute, fatal lung injury when an adult worm dies.
Doses are a clinical reference for licensed veterinary professionals. Always confirm against the current label and the individual patient.
Overview
Montelukast sodium is a leukotriene receptor antagonist. In veterinary medicine, it is primarily used off-label in cats for inflammatory conditions such as:
- Feline asthma
- Inflammatory bowel disease (IBD)
- Chronic upper respiratory infections ("snufflers")
- Heartworm-associated respiratory disease (HARD) syndrome
Clinical Pearl: While theoretically promising for feline asthma by blocking inflammatory mediators, clinical efficacy has been largely disappointing. It is generally considered a second- or third-line adjunctive therapy rather than a primary treatment. A small trial in horses with Recurrent Airway Obstruction (RAO) also failed to show efficacy. In humans, it is FDA-approved for allergic rhinitis and asthma.
Mechanism of action
Montelukast acts as a highly selective and competitive cysteinyl leukotriene receptor (CysLT1) antagonist.
- Arachidonic acid → 5-lipoxygenase pathway → Cysteinyl leukotrienes (LTC4, LTD4, LTE4).
- These leukotrienes are potent inflammatory mediators released by mast cells and eosinophils.
- By blocking the CysLT1 receptor in the airways and gastrointestinal tract, montelukast prevents leukotriene-mediated bronchoconstriction, mucosal edema, vascular permeability, and eosinophil recruitment.
Safety & warnings
Contraindications
- Hypersensitivity to montelukast or any component of the product
- Not for use in reversing acute bronchospasm (asthma attacks)
Adverse effects
- No significant adverse effects reported in cats to date
- Humans (rare): behavioral effects (aggression, suicidal thoughts), palpitations, cholestatic hepatitis, allergic granulomatous angiitis
Precautions
Warnings and Precautions:
- Not a rescue medication: Do not use to attempt to reverse acute bronchospasm or acute asthma attacks.
- Pregnancy/Nursing: Appears safe to use during pregnancy (FDA Category B in humans). Likely safe to use during nursing, though it is excreted in milk.
- Hepatic metabolism: Use with caution in patients with severe hepatic impairment, as the drug is extensively metabolized in the liver.
Drug interactions
CYP-450 enzyme inducer; may reduce montelukast plasma concentrations and efficacy.
CYP-450 enzyme inducer; may reduce montelukast plasma concentrations and efficacy.
Severe peripheral edema has been reported in a human receiving both drugs, presumably due to increased renal tubular sodium and fluid retention. Clinical significance in veterinary patients is unclear.
Monitoring
- Clinical efficacy (improvement in respiratory or GI signs)
Pharmacokinetics
Absorption
No feline data available. In humans: Oral bioavailability is 64%; peak levels occur 3-4 hours after dosing. Presence of food does not affect bioavailability.
Distribution
In humans: Highly bound (99+%) to plasma proteins.
Metabolism
In humans: Extensively metabolized in the liver via cytochrome P450 isoenzymes CYP3A4, CYP2A6, and CYP2C9.
Elimination
In humans: Metabolites are excreted primarily in the bile and eliminated in the feces.
Overdose
Overdose Toxicity: Montelukast is relatively safe in overdose situations.
- Animal Data: Rats and mice survived oral doses of approximately 230X to 335X the usual human adult dose.
- Human Data: Doses as high as 1,000 mg have been reported with the majority having no adverse effects.
- Clinical Signs (if present): Headache, vomiting, psychomotor hyperactivity, thirst, somnolence, mydriasis, hyperkinesia, and abdominal pain.
- Treatment: Basically supportive. No specific antidote is known.
Available products
Formulations
- Oral tablets
- Chewable tablets
- Oral granules
Human-labeled
- Montelukast Sodium Oral Tablets: 10 mg
- Montelukast Sodium Chewable Tablets: 4 mg, 5 mg
- Montelukast Sodium Oral Granules: 4 mg/packet
Regulatory status
No regulatory data for: 🇺🇸 US · 🇪🇺 EU · 🇬🇧 UK · 🇭🇰 HK · 🇹🇼 TW · 🇯🇵 JP · 🇰🇷 KR · 🇦🇺 AU
Storage & stability
Store tablets or granules at room temperature; excursions are permitted to 15°-30°C (59°-86°F). Protect from moisture and light.
Client information
- Administration: May be given with or without food.
- Not a Rescue Drug: This drug is for long-term maintenance and is not for the immediate treatment of acute asthma attacks or severe breathing difficulties.
- Observation: This drug has not been used extensively in animals. Please monitor your pet closely and report any adverse effects (such as behavioral changes or stomach upset) to your veterinarian immediately.
VetSheet drug reference is intended for licensed veterinary professionals as a clinical decision-support aid, not a substitute for professional judgement or the manufacturer’s current label.