Of the 106 dogs diagnosed with AD in the clinical research, the majority (84.5%) were of a defined breed. This finding is consistent with previously published data [7, 19] showing that dogs of many defined breeds are genetically predisposed to developing AD, likely due to a combination of genetic characteristics as well as certain environmental factors [3]. The most frequent breed represented in the present study was shih tzu, which is the most popular dog breed in the southeast Brazil [20].
Approximately 60% of the dogs were females and the body weight of the animals ranged from 2.5 to 39.8 kg (mean 13.8 kg), with more than half of the dogs each weighing between 2.5 and 10 kg, demonstrating a current predominance of miniature and small client owned dogs in Brazil [20].
Based on American laboratory dose titration and clinical dose determination studies with different dosages [4, 10], the minimum effective dosage was determined to be 2 mg/kg. Pharmacokinetic studies also predicted the 2 mg/kg dose would have mAb concentrations above EC50 for 28 days [10]. In the present study, enrollment of animals with more severe AD (VAS ≥ 7 and CADESI-4 ≥ 20) provided an opportunity to evaluate the level of efficacy over the 30-day period for these cases, noting that many other therapeutic options do not provide prolonged efficacy, as demonstrated by the daily administration of cyclosporine over 28 days of evaluation, compared with a single SC administration of lokivetmab at D0 [11]. The 30-day efficacy period also provides a sensible, convenient period for owners to increase treatment compliance. In a clinical trial in client owned dogs with AD, monthly administration of lokivetmab at 2mg/kg (actual doses ranged from 1.0-3.3mg/kg) was noninferior to daily administration with oral cyclosporine at 5mg/kg for pruritus reduction. Mean CADESI-03 scores were not significantly different between the treatments at any time points [11].
In the present study, the mean VAS at D0 was 7.75 which demonstrated a significant reduction within 2 days after treatment, and remaining stable at the improved level throughout the study. Similarly, there was a satisfactory reduction in severity of skin lesion scores. CADESI-4 scores at baseline were reduced by 55% at D30 in agreement with the study by Michels et al [4] where CADESI-4 scores were improved as early as 7 days after treatment. Despite the heterogeneity of lesion severity, the enrollment criteria required each dog to have a CADESI-4 score ≥ 20. Therefore, none of the dogs had a skin condition at D0 that would be considered mild.
When classifying our sample according to CADESI-4 [16], at D0 we obtained 69 dogs classified as “mild” AD (10–34); 21 dogs as “moderate” (35–59) and 12 dogs “severe” (≥ 60). At D30, after application of lokivetmab, 44 dogs were classified as “in remission” (< 10); 45 dogs as “mild”; 8 dogs as “moderate” and only 5 dogs as “severe”, similar to what was previously described [11]. As demonstrated (Fig. 4), the subgroup with the best response to treatment was the “mild” patients on D0, of which 35 progressed to “in remission”.
When evaluating Spearman's correlation between VAS and CADESI-4, there was a positive and significant correlation between these variables, which indicates that as the pruritus improved, so did the skin lesions. This phenomenon had probably occured because of the indirect anti-inflammatory effect of lokivetmab, despite specifically blocking IL-31, also decreased others citocines of the inflammatory cascade [11].
Staphylococcal pyoderma and yeast infections caused by Malassezia spp are the most common infections of the skin and ears in cAD [21]. In this research, associated with clinical improvements, there was also a reduction in Staphylococcus spp infections present on D30. However, 7 dogs developed Malassezia spp infections despite the use of the antiseptic shampoos, and 2 animals developed both infection (Staphyloccocus spp and Malassezia spp). In DeBoer 2008’s study [22], atopic patients have their cellular immunity depressed causing high susceptibility to bacterial and fungal infections. This evidences indicates that this susceptibility maintains the allergic state. In other words, there is the possibility of animals becoming allergic to the microorganisms that constitute their own skin microbiota. In addition, some toxins secreted by Staphylococcus spp can activate T lymphocytes to produce pro-allergic cytokines and perpetuate the symptomatology.
Besides that, higher levels of Malassezia-specific immunoglobulin E have been found in atopic dogs compared with healthy dogs, suggesting that Malassezia may participate as an allergen in patients with AD [23]. The inflammatory condition of this patient favors the proliferation of Malassezia spp, contributing to the worsening of this disease [21].
The adverse events observed following administration of lokivetmab were mild and required no additional treatment or drug intervention. Of the 4 patients that were withdrawn from the present study by the owner, only 1 was due to diarrhea and severe vomiting on D0, following administration of lokivetmab. The appearance and incidence of vomiting, diarrhea, or lethargy reported in the present study are similar to those reported previously in randomized clinical trials of efficacy and safety of lokivetmab in client owned dogs, including one large safety study in dogs with reported comorbidities and only minimal restrictions for concurrent medications during the study [4, 11, 13]. As stated in the conclusions of the researchers in those earlier controlled studies, we found that lokivetmab demonstrated a good safety profile when administered by SC injection to dogs with AD.
OGATE is a relevant, but subjective, tool in assessing adherence and success of the therapeutic regimen [18]. In our sample, 73,5% of the dog owners rated the treatment as good to excellent, indicating a high level of satisfaction. Despite the majority of positive responses and the significant clinical improvement of pruritus and lesion scores achieved in this study, flares related to exposure to allergens are common and may cause some owners to feel that treatment did not provide the expected response [19]. In their development of a core outcome set for evaluating and comparing outcomes of treatments administered to dogs with atopic dermatitis, Olivry and others acknowledge the subjective nature of OGATE, but advise that it is a useful criterion when assessed in concert with results of clinical assessments [18].
A limitation of this study is the absence of a control group. Initially, the study was to be carried out as a randomized clinical trial with a test group (lokivetmab) and a negative (placebo) or positive (corticosteroids, oclacitinib, ciclosporin) control group. However, with regard to a negative control group, we faced an ethical dilemma when we determined there was a severe degree of pruritus and lesions from itching and rubbing. Therefore, it was decided that it would be very difficult to convince the owners that their dogs with severe cAD might only receive a placebo. The other option of using a corticosteroids as a positive control treatment could be problematic for dogs with a long history of using prednisolone or other steroid treatments associated with adverse reactions. Another restriction of the study was an open-label, constituted by domiciled dogs, which were totally dependent on their owners and their monitoring. This situation could overestimate the effectiveness assessment.
It may be possible to provide acceptable efficacy, perhaps with even fewer adverse reactions, with lower dosages of lokivetmab. Results of one clinical study indicated that lokivetmab at 0.5 mg/kg provided significant reductions in lesion scores, although the treatment effect was observed later, and the duration of efficacy was shorter than for the dogs treated with lokivetmab at 2 mg/kg [4].