Treatment of Allergies in Dogs
For dogs with allergies, antihistamines (particularly cetirizine) and glucocorticoids are the primary medications used, while quercetin lacks veterinary evidence and should not be relied upon as a primary treatment.
First-Line Pharmacologic Treatment
Antihistamines
- Cetirizine (2 mg/kg orally twice daily) is the most effective antihistamine for dogs, demonstrating significant reduction in both immediate allergic reactions and late-phase responses in controlled studies 1
- Diphenhydramine (2.2 mg/kg orally twice daily) is commonly used but has failed to show efficacy in preventing cutaneous allergic reactions in dogs, despite reaching therapeutic plasma concentrations 1
- Antihistamines are frequently used as single agents, in combinations, or to reduce glucocorticoid requirements in managing allergic pruritus 2
- H1 receptor antagonists may be needed to manage adverse effects during allergen-specific immunotherapy 3
Glucocorticoids
- Glucocorticoids are effective for controlling clinical signs when other treatments are insufficient 3
- For uncomplicated allergic reactions, diphenhydramine alone produces equivalent outcomes to diphenhydramine plus glucocorticoid combination therapy, with no difference in response rates or need for additional intervention 4
- Short courses of glucocorticoids may be appropriate for severe cases, though 29.6% of dogs undergoing immunotherapy required glucocorticoid supplementation 3
Treatment for Secondary Complications
Infectious Complications
- 74% of allergic dogs develop superficial bacterial pyoderma requiring antibacterial therapy during their disease course 3
- 66.6% require treatment for Malassezia species dermatitis on one or more occasions 3
- 29.6% develop otitis externa due to Malassezia species or bacteria requiring specific treatment 3
Alternative and Adjunctive Therapies
Nonsteroidal Anti-inflammatory Agents
- Tricyclic antidepressants can be useful as single agents or in combination for allergic pruritus management 2
- Omega-3/omega-6 fatty acid-containing products are often helpful, either alone or for reducing glucocorticoid requirements 2
Allergen-Specific Immunotherapy
- Allergen-specific immunotherapy (ASIT) is one of the main treatments for atopic dermatitis in dogs, though it frequently requires additional supportive medications 3
- 18.5% of dogs experience adverse effects from ASIT that may require antihistamine treatment to continue therapy 3
Regarding Quercetin
There is no veterinary evidence supporting quercetin use in dogs with allergies. The provided evidence base contains no studies evaluating quercetin efficacy, safety, or dosing in canine patients. While quercetin is a flavonoid with theoretical anti-inflammatory properties, relying on unproven supplements delays appropriate evidence-based treatment with antihistamines and glucocorticoids that have demonstrated efficacy.
Clinical Algorithm
- For acute uncomplicated allergic reactions: Administer cetirizine 2 mg/kg orally twice daily 1
- If inadequate response: Add short-course glucocorticoid therapy 3
- Monitor for secondary infections: Treat bacterial pyoderma or Malassezia dermatitis as they develop in the majority of cases 3
- For chronic/recurrent allergies: Consider allergen-specific immunotherapy with continued antihistamine support 3
- Avoid diphenhydramine as monotherapy given its lack of proven efficacy in dogs 1
Important Caveats
- Despite diphenhydramine's widespread use in veterinary medicine, controlled studies demonstrate it fails to prevent allergic reactions in dogs, unlike its efficacy in humans 1
- The high incidence of secondary bacterial and fungal infections (74% and 66.6% respectively) means most allergic dogs will require antimicrobial therapy beyond antihistamines alone 3
- Combination therapy with diphenhydramine plus glucocorticoids offers no advantage over diphenhydramine alone for uncomplicated reactions, so glucocorticoids should be reserved for inadequate antihistamine response 4