🌸 Antihistamine

Allegra Dog Dosage Calculator

Calculate fexofenadine (Allegra) doses for dogs with allergic skin disease — a non-sedating second-generation antihistamine with critical Allegra-D pseudoephedrine warning.

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ALLEGRA-D IS TOXIC TO DOGS. Allegra-D and Allegra-D 24-Hour contain pseudoephedrine, which can cause life-threatening stimulant toxicity in dogs (hypertension, tachycardia, seizures). ONLY use plain Allegra (fexofenadine only). Check every label — never assume.

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About Fexofenadine (Allegra / Telfast)

Drug Class

Second-Generation (Non-Sedating) H₁ Antihistamine

Mechanism of Action

Fexofenadine selectively and competitively blocks peripheral H₁ histamine receptors without crossing the blood-brain barrier significantly, producing antipruritic and anti-allergic effects with minimal sedation. It does not have anticholinergic side effects.

Primary Uses in Dogs

Allergic pruritus (atopic dermatitis), environmental and seasonal allergies, urticaria, insect-bite hypersensitivity, and as a safer alternative to diphenhydramine when sedation is undesirable.

Dosing Quick Reference

Indication Dose Frequency
Allergic pruritus 1–2.5 mg/kg q12–24h PO
Urticaria 2 mg/kg q12h PO
Seasonal allergy 1 mg/kg q24h PO long-term

Common Side Effects

  • Mild GI upset (vomiting, diarrhoea) at high doses
  • Occasional sedation (less than older antihistamines)
  • Headache (extrapolated from humans; rare in dogs)
  • Generally very well tolerated

Monitoring

No specific monitoring required for short-term use. Reassess efficacy after 4–6 weeks — antihistamines only help approximately 20–30% of atopic dogs.

⚠️ Fexofenadine is available as 60 mg, 120 mg, and 180 mg tablets — the 60 mg tablet is most practical for small dogs. Avoid combination products (Allegra-D contains pseudoephedrine which is toxic to dogs). Ensure you are using plain fexofenadine only.

What Is Fexofenadine (Allegra) for Dogs?

Fexofenadine is a non-sedating, second-generation H1 antihistamine that selectively and peripherally blocks histamine H1 receptors. Unlike first-generation antihistamines (diphenhydramine, chlorphenamine), fexofenadine has minimal CNS penetration due to efflux by P-glycoprotein, making it non-sedating in most dogs. It is used as adjunct therapy for canine atopic dermatitis, allergic rhinitis, urticaria, and food allergies.

Antihistamines generally have limited efficacy as monotherapy for canine atopy, but provide benefit when combined with omega-3 fatty acids, topical therapy, or allergen-specific immunotherapy. Second-generation agents like fexofenadine are preferred over first-generation due to lower sedation risk and once-daily dosing convenience.

Available Forms

  • 30 mg, 60 mg, 120 mg, 180 mg tablets
  • 6 mg/mL oral suspension (for small dogs)
  • ONLY plain Allegra — never Allegra-D (contains pseudoephedrine)

How to Use This Calculator

  1. Verify your product is plain fexofenadine — read all active ingredients
  2. Enter your dog’s weight
  3. Choose the tablet strength you have
  4. Click Calculate to see daily dose and tablet count

🧮 Fexofenadine Dose Calculator

Fexofenadine Dosing Result

References

  1. Plumb DC. Plumb’s Veterinary Drug Handbook, 9th ed. Wiley-Blackwell; 2018.
  2. Olivry T, et al. Treatment of canine atopic dermatitis: 2015 updated guidelines. BMC Vet Res. 2015;11:210.
  3. ASPCA Animal Poison Control Center. Pseudoephedrine toxicity in dogs. 2023.