Allergen-specific intradermal testing
Effect of oral antihistamines
There are three studies that have examined the influence of oral antihistamines on IDT results.
In one study, 18 dogs with previously positive IDT reactions to flea allergens were treated with hydroxyzine hydrochloride (manufacturer not specified) at 3 mg/kg twice daily orally (p.o.) for 1 or 4 weeks. Intradermal (i.d.) injections of histamine and flea allergens yielded reactions that returned to normal or near normal levels by 5 days after drug cessation. There were no noticeable differences in recovery of IDT reactivity between 1 and 4 weeks of hydroxyzine administration.
In another study, six normal laboratory dogs were given a single dose of 2 mg/kg hydroxyzine pamoate (PCCA, Houston, TX, USA). After 24 h, the inhibition of histamine reactivity was about 40% compared with baseline and half of the maximal inhibition. Extrapolation of the inhibition curve suggested that, by 36 h after drug administration, histamine reactivity would no longer be inhibited.
Finally, 10 house dust mite (HDM)-reactive dogs were treated with cetirizine (Zyrtec; UCB Pharma, Madrid, Spain) at 1 mg/kg once daily p.o. for 7 days. At the end of the 1 week treatment period, IDT reactions to HDM and histamine were inhibited by an average of 49 and 36%, respectively. Reactions had returned to normal values within 7 days of discontinuing cetirizine.
In summary, the results of the two studies performed in dogs with spontaneous hypersensitivity suggest that, by 1 week after oral antihistamine discontinuation, the interpretation of IDT results would be similar, or closely similar, to that done before drug initiation;[6, 8] the OWT was therefore set at 7 days (Table 1). In cases where such delay cannot be considered, the results from the study by Bizikova et al. suggest that 2 days may be a suitable MWT. It is important to keep in mind that such withdrawal times are likely to vary with the type of antihistamine used and its dose, frequency and, perhaps, duration of administration.
Table 1. Summary of optimal and minimal withdrawal times before intradermal and serological tests in dogs
|Antihistamines (oral)||Hydroxyzine, cetirizine||7||2|
|Glucocorticoids (short-acting oral)||Prednisone, prednisolone||14||Unknown|
|Glucocorticoids (long-acting injectable)||Methylprednisolone acetate||Unknown||28|
|Glucocorticoids (topical)||Hydrocortisone, triamcinolone||14 (strong potency)||0 (weak potency)|
|Glucocorticoids (otic)||Betamethasone, mometasone||14||0|
|Essential fatty acids (oral)||Essential fatty acids (various)||0||0|
|IgE serological tests|
|Antihistamines (oral)||Not tested||Unknown||0|
|Glucocorticoids (short-acting oral)||Prednisone, prednisolone||0||0|
|Glucocorticoids (long-acting injectable)||Methylprednisolone acetate||<28||Unknown|
|Glucocorticoids (topical or otic)||Not tested||Unknown||0|
Effect of short-acting oral glucocorticoids
Results from five studies are relevant to the evaluation of the effect of oral glucocorticoids on IDT reactivity.
In the first study, 10 beagles experimentally sensitized to fleas received either 0.55 mg/kg of prednisone (Sigma Chemical Company, St Louis, MO, USA) or placebo twice daily for 5.5 days. Prednisone treatment led to a statistically significant reduction in immediate wheal diameter after injection of flea allergen compared with baseline values, but the average difference at the end of the treatment (<2 mm) would be unlikely to have affected the interpretation of the test. This lack of clinically relevant effect was corroborated by the lack of statistically significant differences in subjective scores during this intervention. In contrast, there was a statistically and clinically significant inhibitory effect of prednisone on the objective and subjective assessment of 24 h late-phase reactions during the study.
In a second study, the IDT reactivity to flea antigen was not significantly different, compared with baseline values, after treatment with prednisone (manufacturer not specified) at 0.5 mg/kg twice daily for 7 days, then once daily for 7 days and then every other day for 14 days. In contrast, treatment with prednisone at 1 mg/kg once daily for 4–6 weeks significantly reduced IDT reactivity to histamine and pollen allergens in experimentally sensitized dogs.
In a third study, eight beagles with flea-allergic dermatitis were treated with prednisolone (manufacturer not specified) at 1 mg/kg/day for 8 weeks. Treatment for 5 weeks did not significantly affect IDT immediate reactivity to the major flea salivary allergen, Cte f 1.
Furthermore, the administration of prednisolone (manufacturer not specified) at 0.5 mg/kg twice daily for 3 days to five laboratory dogs did not seem to affect immediate skin test reactivity to anti-IgE antibodies. However, at the same time, there were no macroscopically evident late-phase reactions in prednisolone-treated dogs, in contrast to the untreated dogs.
Finally, 10 HDM-reactive dogs were treated with oral prednisolone (Deltacortril; Pfizer, Istanbul, Turkey) at 1 mg/kg once daily for 3 days, then 0.5 mg/kg once daily for 2 days and then 0.25 mg/kg once daily for 2 days. After 1 week of treatment, IDT reactions to HDM and histamine were inhibited by an average of 51 and 31%, respectively. Seven days after discontinuation of prednisolone (i.e. study day 14), the surface of IDT reactions had increased markedly compared with the immediate post-treatment values, but HDM and histamine reactions were still significantly lower than at baseline.
In summary, these studies provide conflicting results, implying either a lack of effect on[10-12] or an inhibition of[8-10] immediate IDT reactivity by oral glucocorticoids in dogs. There was, however, a clearer inhibitory effect on IgE-mediated late-phase reaction.[9, 12] Based on the available evidence suggesting a rapid increase in histamine and allergen wheal diameter after prednisolone discontinuation, the OWT should be longer than 7 days. Given a precautionary approach, an OWT of 14 days is proposed, while an MWT cannot be estimated with certainty (Table 1). As a dosage- and time-dependent inhibitory effect on IDT reactivity is suggested by one study, this factor must be taken into account before extrapolating these withdrawal times to other glucocorticoid dosages and durations of administration.
Effect of long-acting injectable glucocorticoids
In a single study evaluating this type of intervention, methylprednisolone acetate (manufacturer not specified) was given at 2 mg/kg subcutaneously (s.c.) twice, 1 month apart, to eight dogs with experimental flea-allergic dermatitis. One month after the second injection, there was an incomplete suppression of immediate IDT reactions to flea salivary allergens compared with reactions of untreated control dogs; further details were not available for review.
In summary, insufficient data are available to generate a meaningful OWT; an MWT of at least 28 days is proposed (Table 1).
Effect of topical glucocorticoids
Four studies have tested the effect of different topical glucocorticoid formulations on IDT reactions in dogs.
In one study, 16 normal dogs were treated with a twice-weekly application of a 1% hydrocortisone leave-on conditioner (ResiCORT; Virbac, Fort Worth, TX, USA) or its vehicle for 6 weeks. Seven pruritic dogs were treated in a similar manner with the hydrocortisone conditioner. After 2, 4 and 6 weeks of this intervention, there was no significant reduction in immediate reactivity to i.d. injections of histamine.
A vehicle-controlled blinded study tested the same conditioner, which was applied to the skin once daily for 3 days. Wheal diameters, but not erythematous flares, after anti-IgE i.d. injections were significantly lower after treatment with the 1% hydrocortisone conditioner than after its vehicle. However, the median decrease in diameter was only 2 mm, which would be unlikely to affect IDT interpretation. In contrast, there was no noted impact on the clinical evaluation of late-phase reactions.
In another experiment, a 0.0584% hydrocortisone aceponate spray (Cortavance; Virbac, Carros, France) was applied to both axillae, the groin and one side of the thorax of 10 Maltese–beagle atopic dogs once daily for 14 days. After 7 and 14 days, there was a significant inhibition of immediate reactivity after i.d. injections of histamine and anti-IgE antibodies on the treated side of the thorax. Immediate IDT reactions were also reduced on the untreated side of the thorax after 14 days. Late-phase reactions after anti-IgE i.d. injections were significantly reduced on both treated and untreated sides of the thorax after 7 and 14 days. Normal to near normal immediate reactivity to histamine returned at untreated sites within 2 weeks of discontinuation of treatment.
Finally, sprays containing either 0.015% triamcinolone (Genesis; Virbac, Fort Worth, TX, USA) or 1% hydrocortisone plus 1% pramoxine (Relief HC; Teva Animal Health, St Joseph, MO, USA) were applied once daily for 1 week to the axillae, groin and one side of the thorax of 10 Maltese–beagle atopic dogs. Immediate reactions to i.d. injections of histamine and anti-IgE antibodies were significantly decreased for at least 1 week post-treatment on the treated side of the thorax of dogs that received triamcinolone compared with those treated with hydrocortisone and pramoxine; there was no significant inhibition of IDT reactions on the untreated side of the thorax.
In summary, the variability of the study designs and products used renders the determination of universal OWT and MWT difficult. Nevertheless, based on the evidence available from the testing of a potent topical glucocorticoid (Cortavance; Virbac, Carros, France), an OWT of 14 days is proposed (Table 1). For lower-potency topical glucocorticoid formulations, an MWT of 0 days is likely to be possible.[14, 15, 17]
Importantly, two studies have confirmed that a difference in IDT reactivity might occur between sites previously treated with a topical glucocorticoid and areas distant from application sites.[16, 17] This factor must be taken into consideration, and it is recommended that IDT be performed away from glucocorticoid application areas; how great that minimal distance should be is unknown.
Effect of otic glucocorticoids
Only two studies evaluated the influence of glucocorticoid-containing otic formulations on IDT results in dogs.
In the first study, eight dogs were treated with a 0.088% betamethasone-containing otic ointment (Otomax; MSD Animal Health, Carbajosa de la Sagrada, Spain) twice daily for 2 weeks. At the end of treatment, the immediate IDT reactivity to histamine and two of seven tested allergens was statistically significantly reduced compared with pretreatment values. However, the average reduction in IDT reaction diameters was less than 1 mm, and it is unlikely that this intervention would have affected IDT interpretation.
In the second study, 20 dogs with AD were treated with a 0.1% mometasone furoate-containing otic suspension (Mometamax; Merck Animal Health, Summit, NJ, USA) once daily for 14 days. In three dogs, wheal scores after i.d. injections of histamine and anti-IgE antibodies were within 25% of pretreatment values 7 days after discontinuation of treatment. In all other dogs, wheal scores returned to similar levels within 14 days of drug withdrawal.
In summary, both these studies established that the use of a glucocorticoid-containing otic formulation can significantly reduce IDT immediate-phase reactivity, but the magnitude of the reduction is unlikely to affect IDT interpretation greatly, unless, perhaps, reactions are borderline positive.[18, 19] While an OWT of 14 days might be necessary to eliminate any risk of drug interference, especially for weak reactions, an MWT of 0 days could be considered after verification of appropriate reactivity to positive controls (Table 1).
Effect of oral ciclosporin
Four studies tested the influence of oral ciclosporin on IDT in dogs.
In one study, ciclosporin (Atopica; Novartis Animal Health, Basel, Switzerland) was administered at 5 mg/kg p.o. once daily for 6 weeks to six dogs with AD. There were no statistically significant differences in positive (i.e. moderate to strong) reactions to environmental allergens before and after treatment.
In a second study, eight beagles with flea-allergic dermatitis were treated with ciclosporin (Neoral; Novartis, Basel, Switzerland) at 5 mg/kg p.o. once daily for 8 weeks. After 5 weeks, ciclosporin had not significantly altered the IDT immediate reactivity to Cte f 1, the major flea allergen.
In another trial, 16 dogs with AD were randomly given either placebo or ciclosporin (Atopica; Novartis Animal Health, Basel, Switzerland) for 30 days at 5 mg/kg once daily. Similar to the results of the other trials, ciclosporin did not significantly inhibit IDT immediate reactivity to the tested allergens compared with placebo.
In contrast to these three studies, ciclosporin (Neoral; Novartis, Basel, Switzerland) given at the same dosage (5 mg/kg once daily) to four laboratory dogs for 30 days was found to attenuate significantly IDT immediate reactivity to Ascaris allergen, and the reduction in reactivity was correlated with lower levels of histamine amounts collected by dermal microdialysis.
In summary, while one experimental study found some inhibitory effect of ciclosporin on the IDT result for one allergen, three studies including dogs with spontaneous AD found no such inhibition.[11, 20, 21] As a result, a withdrawal of short-term (i.e. 6–8 weeks) ciclosporin is probably not needed prior to IDT (Table 1).
Effect of topical tacrolimus
A 0.1% tacrolimus ointment (Protopic; Astellas Pharma, Northbrook, IL, USA) was applied to the lesional skin of nine house dust- or HDM-sensitive dogs with AD once daily for 4 weeks. After 4 weeks of tacrolimus, immediate IDT reactions to histamine, allergens or lipopolysaccharide were not significantly different from baseline values. In contrast, some of the late-phase reactions to allergens were significantly reduced by tacrolimus. Late-phase reactions took up to 4 weeks to return to pretreatment values, but by 2 weeks after discontinuation of treatment, the 4 h reaction to house dust as well as the 4 and 6 h late-phase reactions to HDM had returned to normal.
In summary, topical tacrolimus does not appear to interfere with immediate IDT reactions performed outside of the treatment area; however, late-phase reactions might be affected. Withdrawal times of 0 days for immediate IDT reaction evaluation and 14 days for late-phase reaction grading are proposed (Table 1).
Effect of oral pentoxifylline
Ten HDM-hypersensitive atopic dogs were treated with oral placebo or pentoxifylline (Trental; Hoechst-Roussel Pharmaceutics, Trenton, NJ, USA) at 10 mg/kg twice daily for 4 weeks. After treatment with pentoxifylline, there was no significant inhibition of immediate IDT reactions to HDM allergens compared with baseline values. In contrast, late-phase reactions to lipopolysaccharide were significantly decreased in comparison to pretreatment and placebo scores.
In summary, as pentoxifylline, at low dosages, does not appear to interfere with the immediate IDT reaction to environmental allergens, a withdrawal of pentoxifylline is not needed prior to IDT (Table 1). Late-phase reactions are likely to be altered by pentoxifylline therapy, but specific withdrawal times for such reactions could not be assessed.
Effect of oral ketoconazole
Twelve HDM-sensitized dogs with AD received ketoconazole (Nizoral; Janssen, Titusville, NJ, USA) at 5 mg/kg twice daily for 3 weeks. Treatment with ketoconazole did not affect immediate IDT reactivity to histamine or HDM allergens.
In summary, because of the lack of detected interference of ketoconazole on the immediate IDT reaction to HDM allergens and histamine, a withdrawal of ketoconazole is not needed before IDT (Table 1).
Effect of oral essential fatty acids
Two fatty acid supplements (Efavet Regular or HGF; Efamol Vet, Guildford, UK; now MSD Animal Health, Milton Keynes, UK), were given for up to 118 weeks to 20 dogs with AD. Overall, treatment with these fatty acid supplements did not alter the immediate IDT reactivity to histamine. There was an occasional reduction in average wheal diameter after the injection of some allergens, but this change would have been unlikely to have affected the interpretation of IDT results.
In summary, there are numerous formulations of essential fatty acids available for animal use, but only one study evaluated whether these supplements would affect immediate IDT reactivity. As this study did not report any difference in immediate IDT results during fatty acid supplementation, a withdrawal of fatty acids prior to the performance of IDT does not appear to be needed (Table 1).
Allergen-specific IgE serological testing
Effect of oral antihistamines
The effect of type 1 antihistamines on ASIS has not been studied in dogs. However, the antagonism of the type 1 histamine receptor by antihistamines should not, at least in theory, interfere with the measurement of allergen-specific IgE in the patient's serum. As a result, a withdrawal of antihistamines before ASIS is theoretically not needed, but this assertion remains unproven.
Effect of short-acting oral glucocorticoids
There are two studies that have tested the influence of oral glucocorticoid on IgE serological tests.
In one study, prednisolone or prednisone (manufacturer not specified) was administered to 15 dogs with AD at 1.1 mg/kg once daily for 1 week and then every other day for 2 weeks. Overall, this had no effect on the interpretation of the ASIS results (Bioproducts DVM, Inc., Tempe, AZ, USA).
In a second study described in the preceding IDT section, prednisolone was administered to eight dogs with flea-allergic dermatitis at 1 mg/kg/day for 8 weeks. After 5 and 7 weeks of treatment, there were no significant differences in Cte f 1-specific IgE serum levels (Heska Corporation, Loveland, CO, USA) compared with baseline values.
In summary, based on the limited data available for review,[11, 28] oral glucocorticoids given at anti-allergic dosages for less than 2 months are unlikely to have an effect on IgE serological tests (Table 1). A withdrawal time of 0 days is proposed.
Effect of long-acting injectable glucocorticoids
In one study already described in the IDT section above, eight dogs with experimental flea-allergic dermatitis were treated with methylprednisolone acetate (manufacturer not specified) at 2 mg/kg s.c. twice, 1 month apart. One month after the second injection, there was no reported inhibition of serum levels of IgE specific for flea salivary allergens (Heska Corporation).
In summary, insufficient data are available to estimate an accurate OWT, but study results suggest that it may be less than 28 days (Table 1).
Effect of topical and otic glucocorticoids
The effect of topical and otic glucocorticoid formulations on ASIS has not been tested in dogs. However, as prednisolone given p.o. for 7 weeks did not affect IgE serological test results, it is unlikely that topical or otic glucocorticoids would do so either. Consequently, an MWT of 0 days is proposed.
Effect of oral ciclosporin
Three studies evaluated the influence of oral ciclosporin on the results of ASIS.
In the first study, eight beagles with experimental flea-allergic dermatitis received ciclosporin (Neoral; Novartis, Basel, Switzerland) at 5 mg/kg/day once daily for 8 weeks. After 5 and 7 weeks of treatment, there were no reported relevant changes in Cte f 1-specific IgE serum levels (Heska Corporation).
In a second study, ciclosporin (Atopica; Novartis Animal Health, Basel, Switzerland) was administered to 16 dogs with AD for 30 days at 5 mg/kg once daily. This regimen did not significantly alter ASIS results (Heska Corporation).
Finally, ciclosporin (Neoral; Novartis, Basel, Switzerland) was given at the same dosage (5 mg/kg once daily) to four laboratory dogs for 30 days. This regimen did not result in a significant change in the dogs' total IgE serum levels determined using a research laboratory ELISA (Bethyl Laboratories, Montgomery, TX, USA).
In summary, based on this evidence,[11, 21, 22] ciclosporin given for up to 2 months at dosages used for the treatment of canine AD does not appear to affect the interpretation of ASIS results. As a result, a 0 day OWT is proposed (Table 1).