The use of compound 48/80 and codeine phosphate as positive controls for intradermal skin testing in dogs

Equivalence in intradermal reactions to histamine and compound 48/80 in dogs before and after sedation with dexmedetomidine or a 1:20 combination of medetomidine and vatinoxan

BACKGROUND

Intradermal allergen testing (IDAT) is commonly used to formulate allergen-specific immunotherapy, a pillar treatment for canine atopic dermatitis. Many sedatives have shown histaminergic or anti-histaminergic effects and thus been deemed unsuitable for IDAT.

OBJECTIVE

The goal of this study was to determine whether, in healthy dogs, dexmedetomidine (Dexdomitor) or a 1:20 combination of medetomidine and vatinoxan (Zenalpha) will affect intradermal reactions compared to unsedated dogs.

ANIMALS

Ten privately owned healthy dogs were enrolled in this equivalence study.

MATERIALS AND METHODS

Wheal formation was subjectively and objectively assessed in conscious then sedated dogs. Dogs were randomly sedated with either Dexdomitor (dexmedetomidine [0.5 mg/m2]) or Zenalpha (medetomidine [1 mg/m2/vatinoxan] 20 mg/m2) intramuscularly. Once sedated, five 10-fold histamine (100-0.01 μg/mL) and compound 48/80 (200-0.02 μg/mL) dilutions were intradermally injected into the lateral thorax. The study was repeated on the opposite side with the alternative sedation 1 week later. Quality of sedation, cardiorespiratory function and rectal temperature were recorded every 5 min.

RESULTS

There was no difference in the median values of the reactions with either sedative when compared to unsedated dogs. Dexdomitor and Zenalpha achieved an equivalence in both subjective and objective scoring systems for all concentrations tested. A faster median time to sedation (10 vs. 18 min, p = 0.013) was seen with Zenalpha compared to Dexdomitor. Although both sedatives depressed the cardiovascular function, such parameters were less affected by Zenalpha than by Dexdomitor (p ≤ 0.001).

CONCLUSIONS AND CLINICAL RELEVANCE

Owing to the lack of effects on wheal formation, both sedatives are appropriate for sedating dogs undergoing IDAT. Although, such results should be validated in allergic dogs. Zenalpha may induce more rapid and reliable sedation than Dexdomitor.

Novel phenotype in beagle dogs characterized by skin response to compound 48/80 focusing on skin mast cell degranulation

Beagle dogs have long been employed in toxicology studies and as skin disease models. Compared with other experimental animal species, they are known to be susceptible to skin responses, such as rashes, from exposure to various chemical compounds. Here, a unique dog phenotype was identified that showed no skin response to compound 48/80, a mast cell degranulating agent. Although the skin responses to intradermal injection of polyoxyethylene castor oil derivative (HCO-60, a nonionic detergent), histamine dihydrochloride, concanavalin A (IgE receptor-mediated stimuli), or calcium ionophore A23187 were comparable in wild-type (WT) dogs and these nonresponder (NR) dogs, only the response to compound 48/80 was entirely absent from NR dogs. The skin mast cell density and histamine content per mast cell were histologically comparable between WT and NR dogs. By checking for skin responses to compound 48/80, NR dogs were found to exist at the proportion of 17-20% among four animal breeders. From retrospective analysis of in-house breeding histories, the NR phenotype appears to conform to the Mendelian pattern of recessive inheritance. The standard skin response in WT dogs developed at 2-4 months of age. In conclusion, this unique phenotype, typified by insensitivity in the compound 48/80-induced degranulation pathway in mast cells, has been widely retained by recessive inheritance in beagle dogs among general experimental animal breeders. The knowledge concerning this phenotype could lead to better utilization of dogs in studies and aid in model development.

Comparison of subjective and objective intradermal allergy test scoring methods in dogs with atopic dermatitis

An intradermal allergy test (IDT) is an important diagnostic tool for identifying offending allergens in canine atopic dermatitis. No standardized method of scoring an IDT has been described. The purpose of this study was to determine whether there is a correlation between a conventional, subjective IDT scoring method based on perceived wheal diameter, erythema, and turgor (0-4+) and an objective scoring method based on measuring wheal diameter alone. Thirty-four atopic dogs were skin tested with 68 different allergens. All skin tests were performed according to standard procedures, and any IDT score ≥2+ was considered clinically significant. When the subjective IDT scores were compared with the objective IDT scores in all dogs, there was a moderate level of correlation overall (r=0.457; P <0.0001). The highest level of agreement between subjective and objective scores was noted with the reactions assigned subjective scores of "0" and "2+." Overall, there was a slight level of agreement between subjective and objective scores based on clinical significance (i.e., subjective scores ≥2+; κ=0.20; P <0.0001). In conclusion, the authors believe that the objective scoring method used in this study may provide a point of reference for inexperienced individuals (dermatology residents, veterinarians, technicians) when learning to grade an IDT.

Effects of otic betamethasone on intradermal testing in normal dogs

Otitis externa is common in atopic dogs and is frequently treated using potent glucocorticoids topically. These preparations can cause adrenal suppression and affect skin test reactivity. The purpose of this study was to determine if an otic product containing betamethasone could decrease skin reactivity in normal dogs. Sixteen laboratory beagles were used in a cross-over, blinded trial. Dogs were enrolled in two groups; one received placebo and the other a betamethasone-containing otic preparation (Otomax) twice daily for 2 weeks. After a 4-week wash-out period, treatments were switched. Dogs were intradermally tested on days 0 and 14 of each treatment period with histamine phosphate (1 : 100,000 and 1 : 200,000 w/v) and allergens common in the area. Adrenocorticotropic hormone (ACTH) stimulation tests were done before and after treatment to investigate adrenal suppression. After 2 weeks of otic betamethasone, Dermatophagoides farinae (P = 0.0034), Cynodon dactylon (P = 0.0459) and histamine 1 : 100,000 w/v (P = 0.0028) reactions were significantly reduced. Pre-treatment post-ACTH serum cortisol levels and those obtained after both treatments did not differ statistically (P = 0.6362). Betamethasone induced a slight but statistically significant elevation (P = 0.0002) of serum alkaline phosphatase. Despite the increase, values were within normal range. It is concluded that, although otic betamethasone did not suppress adrenal glands, it mildly suppressed intradermal reactions to 1 : 100,000 w/v histamine, D. farinae and C. dactylon.

Comparison of results for intradermal testing between clinically normal horses and horses affected with recurrent airway obstruction

OBJECTIVE

To evaluate differences in response to ID injection of histamine, phytohemagglutinin (PHA), and Aspergillus organisms between clinically normal horses and horses with recurrent airway obstruction (RAO).

ANIMALS

5 healthy adult horses and 5 adult horses with RAO.

PROCEDURE

Intradermal testing (IDT) was performed on the neck with 2 positive control substances (histamine and PHA) and a mixture comprising 5 Aspergillus species. Four concentrations of each test substance plus a negative control substance were used. Equal volumes (0.1 mL) of each test substance were prepared to yield 15 syringes ([4 concentrations of each test substance plus 1 negative control substance] times 3 test substances) for each side of each horse (ie, 30 syringes/horse). Intradermal injections were administered; diameter of wheals was recorded 0.5, 4, and 24 hours after injection.

RESULTS

Hypersensitive responses to ID injection of histamine were detected 0.5 hours after injection, and a delay in wheal formation after ID injection of Aspergillus mixture 24 hours after injection was detected in RAO-affected horses but was not observed in clinically normal horses. No differences were detected between the 2 groups after ID injection of PHA.

CONCLUSIONS AND CLINICAL RELEVANCE

RAO-affected horses are hypersensitive to histamine, suggesting that RAO is associated with a heightened vascular response to histamine. Higher concentrations of Aspergillus mixture may be needed to detect horses that are sensitive to this group of antigens. Wheal reactions to Aspergillus may be a delayed response, suggesting that IDT results should be evaluated 0.5, 4, and 24 hours after ID injection.

Evaluation of the precision of intradermal injection of control substances for intradermal testing in clinically normal horses

OBJECTIVE

To evaluate the precision of intradermal testing (IDT) in horses.

ANIMALS

12 healthy adult horses.

PROCEDURE

IDT was performed on the neck of each horse by use of 2 positive control substances (histamine and phytohemagglutinin [PHA]) and a negative control substance. An equal volume (0.1 mL) for each injection was prepared to yield a total of 20 syringes ([4 concentrations of each positive control substance plus 1 negative control substance] times 2 positive control substances times 2 duplicative tests) for each side of the neck. Both sides of the neck were used for IDT; therefore, 40 syringes were prepared for each horse. Hair was clipped on both sides of the neck, and ID injections were performed. Diameter of the skin wheals was recorded 0.5, 4, and 24 hours after ID injection.

RESULTS

Intra- and interhorse skin reactions to ID injection of histamine and PHA resulted in wheals of uniform size at 0.5 and 4 hours, respectively. Significant intra- and interhorse variation was detected in wheals caused by PHA at 24 hours.

CONCLUSIONS AND CLINICAL RELEVANCE

ID injection of histamine and PHA caused repeatable and precise results at 0.5 and 4 hours, respectively. Concentrations of 0.005 mg of histamine/mL and 0.1 mg of PHA/mL are recommended for use as positive control substances for IDT in horses. This information suggests that consistent wheal size is evident for ID injection of control substances, and variation in wheals in response to ID injection of test antigens results from a horse's immune response to specific antigens.

The ACVD task force on canine atopic dermatitis (XVII): intradermal testing

Intradermal testing has been practiced for decades in human and veterinary medicine. The primary utility of intradermal testing is in the demonstration of IgE-mediated allergen hypersensitivity. The presence of a positive reaction on an intradermal test is not always indicative of allergy, as it may sometimes be an indication of sub-clinical hypersensitivity. Despite its widespread use by veterinary dermatologists, the usefulness of the intradermal test would be greatly enhanced by the use of standardized allergen extracts and homogeneous criteria for the interpretation of results. Irrespective of these shortcomings, intradermal testing is regarded as a valuable tool in the demonstration of allergen-specific hypersensitivity when performed according to accepted guidelines.