Management of allergic dermatitis can be very complex and frustrating. It is very important to emphasise to the client that this condition cannot be cured, but will need to be managed when the symptoms are present and treatment will probably be lifelong.
Treatment of allergic dermatitis must be tailored to the specifc signs and secondary changes or complications present in an individual animal. Owners need to be aware that it is not possible to predict initially which animal will respond to a particular therapy. They also need to understand that clinical manifestations frequently change, resulting in the need to adjust the therapy. Also, it is necessary for the owner to appreciate the time and fnancial
commitment needed for the management of atopic dermatitis.
Long-term ﬂea and parasite prevention should be instituted.
Avoidance of allergens
If a food allergy is deemed to be all or part of the dog’s problem, the offending foods must be eliminated from the diet. It may be possible to avoid some environmental allergens, but this is usually diffcult and of limited beneft.
Topical steroids are very useful for short- or longterm intermittent management of localised lesions. Combinations of steroids with antibiotics and antifungals are very helpful for infected areas, such as the ears, feet or under the neck. Using topical steroids for over 2 months can cause signifcant skin thinning and hair loss, which may take years to resolve. Ideally animals should be maintained on less potent products (e.g. hydrocortisone or hydrocortisone aceponate) that are less likely to cause side effects and the frequency should be tapered to the
lowest frequency needed. Nevertheless, some pets will still have systemic absorption and side effects, and animals on long-term treatment should have regular rechecks. Owners should wear gloves to apply these products.
Topical 0.1% tacrolimus is expensive, but can be very useful to avoid cutaneous atrophy or systemic absorption. Owners should wear gloves and use twice daily until improvement, before tapering to the lowest frequency that maintains remission (ideally twice weekly).
Topical antibiotics and antifungals work well to spot treat small areas but are very diffcult for larger areas. Sprays, ointments, creams or lotions would need to be used twice daily to resolve an infection. Topical sensitivities can occasionally develop.
Shampooing is a very useful and important therapy in pruritic, greasy and/or infected skin. Bathing with lukewarm water with or without a shampoo is also helpful to rinse off allergens before they are absorbed percutaneously. Whirlpool baths are more effective than showers. The shampoo formulation and frequency should be based on cytology and coat greasiness. Bathing should typically be performed one to three times weekly until the clinical signs are controlled. Chlorhexidine products are the most effective antimicrobials, but may be drying and topical sensitisation can occur, including sensitisation in owners. Dogs with pruritic dry skin should be treated with an emollient product with proven antipruritic effcacy. Antiseborrhoeic shampoos can be used in dogs with greasy skin, although care should be taken to avoid over-drying the coat. Emollient leave-on lotions, foams and conditioners can be used where necessary to prevent dryness after or between baths. Owners should be discouraged from scrubbing or picking at the skin, and should not rub against the grain of the hair because this may cause folliculitis in a sensitive dog.
Spot-on therapies can help restore the skin barrier in localised areas of chronic cases. This may be more helpful for some dogs than others. There is only a mild-to-moderate improvement, and frequent use and several doses per pet are needed.
Ear infections respond best to topical medications in the short term. Topical steroids can be used two to three times weekly to prevent recurrent inﬂammation. These can be used alone or combined with cleaning where necessary.
Conjunctivitis can be effectively managed with glucocorticoid-containing ophthalmic preparations (e.g. 1% prednisolone or 0.1% dexamethasone) used three to four times daily to remission, and then tapered for maintenance. Ciclosporin 0.2% ointment applied twice daily to remission and then tapering the frequency is also effective.
Systemic control of infections:
Recurrent yeast and bacterial infections indicate that the atopic dermatitis is not controlled. Efforts should be made to better control the underlying problem and use topical antimicrobials to minimise the repeated use of systemic antimicrobials.
Antibacterial agents for secondary staphylococcal infections include cefalexin (25 mg/kg po q12 h), cefpodoxime proxetil (5–10 mg/kg po q24 h), oxacillin or dicloxacillin (20 mg/kg po q12 h), clindamycin (5.5–11 mg/kg po q12 h), lincomycin (22 mg/kg po q12 h) and clavulanic acid–potentiated amoxicillin (25 mg/kg po q12 h).
Antifungal agents to control secondary Malassezia infection include ketoconazole, itraconazole and ﬂuconazole (5–10 mg/kg po q24 h).
Systemic anti-inﬂammatory therapy
There are a variety of treatment options, but those with good evidence of high effcacy thus far are broad-spectrum agents that target lymphocytes and inﬂammatory pathways (steroids, oclacitinib and ciclosporin) or precise pruritus pathways (interleukin [IL]-31 monoclonal antibody). Other agents are rarely effective by themselves and are most useful as adjunctive therapy.
Essential fatty acid (EFA)–rich diets or supplements may help coat texture and skin barrier function, but most have unproven effcacy in controlling symptoms of atopic dermatitis.
Antihistamines may be effective in some dogs with mild pruritus but are mostly used to reduce the dose and/or frequency of other treatments. They are most effective given before and not after a ﬂare. The sedative effect may help reduce sleep deprivation in pruritic dogs (and their owners). Adverse effects are uncommon but include sedation, excitation and gastrointestinal upsets. The second-generation drugs can induce potentially fatal cardiac arrhythmias. Antihistamines may lower the seizure threshold. Two-week trials with different antihistamines may help determine which is most useful:
• Chlorpheniramine (0.4 mg/kg po q8 h).
• Diphenhydramine (2–4 mg/kg po q8 h).
• Hydroxyzine (2 mg/kg po q8 h).
• Clemastine fumarate (0.05 mg/kg po q8 h).
• Ketotifen (2–4 mg/kg po q8 h).
Glucocorticoids rapidly and reliably control acute or severe symptoms of allergic dermatitis. Methylprednisolone (0.4–0.8 mg/kg) is the drug of choice. Prednisolone and prednisone may also be used (0.5–1.0 mg/kg), but they are more likely to cause polyuria/polydipsia and polyphagia in some dogs. Induction doses should be given twice daily
for 7 days or until remission, then once daily in the morning for 7 days, and then on alternate mornings. The dose can then be reduced to the lowest required to control the clinical signs. Injectable steroids may be warranted if only one to three injections are needed per year to control a seasonal allergy, and if the client fnds it impossible to administer oral medications. As a result of potential adverse effects of glucocorticoids, long-term use is not recommended unless other treatments cannot be used. Adverse effects of systemic glucocorticoids are numerous, including (but not limited to) polyuria, polydipsia, polyphagia, weight gain, panting and mood changes (including aggression). The onset of iatrogenic hyperadrenocorticism is dose and duration dependent, but varies between individual dogs. egular monitoring is necessary to ensure that appropriate doses are being given and that the dog is not developing iatrogenic Cushing’s syndrome. Regular urinalysis and blood pressure monitoring are advisable.
Ciclosporin is a calcineurin inhibitor and immunomodulating agent that is useful for lymphocytic and granulomatous inﬂammation, including atopic dermatitis. The recommended dose for dogs is 4–7 mg/kg po q24 h. Ciclosporin is best suited to chronic use because it can take 2–6 weeks to see clinical improvement. Oral steroids or oclacitinib can be coadministered for 2–3 weeks to give initial relief. Once disease has been controlled on ciclosporin alone, the frequency of dosing can be changed to every other day for 1 month and then, if still controlled, to twice weekly. A rough guideline would be that approximately 30% of cases can be maintained on alternate-day dosing and another 15–20% can be maintained with every third day dosing.11 The dose can be tapered in dogs that require ongoing daily therapy. Satisfactory control of lesions will occur in approximately 60–80% of the cases treated with ciclosporin. Urine samples should be checked every 6–12 months but routine blood work is not needed. Emesis is a major side effect of this treatment and is reported to occur in 14–40% of cases.11 In most cases, an animal will tolerate the drug after a few days and giving the drug after a meal will help. The problem may also be reduced by giving a partial dose after a meal for 3 days, then increasing the dose every 3 days until the recommended dose is reached. Metoclopramide (0.2–0.4 mg/kg po), sucralfate (0.5–1.0 g/dog po), ranitidine (1 mg/kg po) or cimetidine (5–10 mg/kg po) given 30 minutes before dosing may also decrease the frequency of emesis. Some animals will not tolerate the drug and it has to be discontinued. Other less common side effects are diarrhoea, gingival hyperplasia, papilloma-type lesions of the epidermis, hirsutism and a psoriasiform–lichenoid-like dermatitis with coccoid bacteria. In rare instances, diabetes mellitus, pinnal erythema, lameness and muscle pain may be observed. Ciclosporin is contraindicated in the presence of neoplasia, although there is no evidence that it induces neoplasia. Ciclosporin is metabolised by the liver, so caution should be used if the animal to be treated has liver disease, because very high blood levels will develop. In these cases, blood level assays should be performed and the dose adjusted accordingly. In animals without liver disease, blood levels are fairly consistent, so monitoring is not necessary. Drugs that inhibit cytochrome P450 microsomal enzyme activity (e.g. ketoconazole, itraconazole, ﬂuconazole, erythromycin and allopurinol) can result in very high blood levels of ciclosporin and potentiate possible toxicity or other side effects. Ketoconazole (2.5–5 mg/kg with ciclosporin) or ﬂuconazole (5 mg/kg with ciclosporin) have been used commonly to divide the dose of ciclosporin in half to save on cost, and have the same effectiveness. Conversely, drugs that increase cytochrome P450 metabolism (e.g. phenobarbital and trimethoprim–sulphonamides) may reduce plasma levels of ciclosporin.
Oclacitinib should be given at a dose of 0.4–0.6 mg/kg twice daily for 14 days and then once daily thereafter. If symptoms are completely controlled, this drug should be further tapered to the lowest dose needed, although most dogs will still require once-daily therapy. The pruritus often worsens when the dose is reduced to once daily, and some dogs require long-term treatment every 12 hours. It is recommended to check complete blood count, serum biochemistry and urinalysis before therapy, at the 2-month point and then at least yearly. Bone marrow suppression is a rare but possible side effect. This drug is not approved for dogs aged less than 12 months. Skin and ear infections, demodicosis, weight gain, aggression or anxiety and pneumonia have been seen while dogs are on this drug (especially if long-term, twice daily medication is required). Oclacitinib is contraindicated in the presence of neoplasia, although there is no evidence that it induces neoplasia.
IL-31 monoclonal antibody effectively reduces pruritus in about 80% of dogs with atopic dermatitis. The antibody blocks IL-31, which is an important cytokine involved in early inﬂammation and pruritus in canine atopic dermatitis. The effectiveness peaks at day 7 and then declines, with repeated treatment required every 25–35 days in most cases. Long-term studies of safety had not been performed by the time of this publication, but it seems to have very few side effects and is well tolerated.
Recombinant canine interferon-γ or feline interferon-ω, given orally or subcutaneously, appears to be somewhat effective in the management of some long-term cases,12,13 but availability is limited for many countries. The benefts may take several months to become apparent. No large studies have been performed.
Allergen testing and allergen-specifc immunotherapy:
Current allergen tests detect the presence of allergen-specifc IgE antibodies. Not all atopic dogs produce IgE in response to allergens. If properly performed, intradermal allergen testing will result in positive results that concur with the history in approximately 85% of cases. To prevent inaccurate test results, antihistamines (including behavioural medications) should be discontinued 7 days before testing, oral and topical steroids 2 weeks before testing and repository injectable steroids 6–8 weeks before testing. There are no withdrawals needed for ciclosporin, oclacitinib, IL-31 monoclonal antibody or EFAs. If this procedure is not performed routinely, or if the clinician has not had appropriate training, referral is recommended.
Serum tests (radioallergosorbent test [RAST], enzyme-linked immunosorbent assay [ELISA] and liquid-phase immunoenzymatic assay) are simpler to perform in practice and can be used to detect increased concentrations of allergen-specifc IgE. The major problem with these tests is lack of specifcity. Almost all non-allergic dogs react to at least one and sometimes many allergens.15 There is moderate intra- and interlaboratory variability in Results. However, in some situations, serological testing may be helpful in the selection of allergens for immunotherapy. Serological testing for food allergens is neither accurate nor recommended, and food trials must be performed for diagnosis of food allergy.
Allergen-specifc immunotherapy (ASIT) by subcutaneous injection (SCIT), intralymphatic injection (ILIT) or sublingual immunotherapy (SLIT) drops has been reported to result in at least a 50% improvement in 65–70% of atopic dogs, although most dogs will not completely respon dto ASIT alone. It may take animals as long as 6–12 months (and sometimes longer) to respond to immunotherapy and, therefore, critical clinical evaluation should not take place until a year of therapy has been completed. Other concurrent therapy is therefore appropriate. Adverse effects are uncommon. Injection site reactions and anaphylactic shock are rare, and most dogs tolerate the injections with little discomfort. Mild reactions can generally be prevented by pretreating with antihistamines 1–2 hours before the injection if necessary. The intervals between injections can be individualised to the needs of each animal.Using SLIT avoids injections and is very safe, but it needs to be given every 12 hours. Little research on the effectiveness of SLIT has been performed in dogs. Discussing the pros and cons of each form of ASIT will help owners choose the format that best suits them and their dog. Dogs that fail to respond to one form of ASIT may still respond to another. ASIT works by inducing tolerance to the allergens. It therefore prevents ﬂares associated with future exposure to the allergens, rather than acting as an anti-inﬂammatory.
Regular treatment is often necessary to maintain tolerance, but it is possible to make permanent changes and taper therapy off after 2–4 years of treatment in some dogs. Some dogs, however, will relapse on weaning of ASIT. Retesting may reveal new sensitivities in dogs that relapse while on ASIT, and reformulating their ASIT can be benefcial.
• The diagnosis of atopic dermatitis is based on a characteristic history, the typical clinical signs, ruling out other pruritic diseases and the response to therapy.
• Allergy tests are not diagnostic for the disease – food trials and allergy tests are used to determine the food and/or environmental allergens to which each dog is sensitised.
• Therapy is typically multi-modal and needs to be constantly modifed to best suit each dog’s symptoms. Typically, treatment is based around skin barrier care, allergen avoidance and ASIT, and anti-inﬂammatory therapy.
• Proactive therapy that maintains remission is more effective than simply reacting to recurrent ﬂares.
• Most dogs with recurrent staphylococcal or Malassezia skin and ear infections have unmanaged atopic dermatitis.