MANAGEMENT OF ALLERGY TO ANIMAL DANDERS

Abstract

As represented in Table 2, a total of nine studies on animal dander immunotherapy has been reported since 1978. Five of these studies, with a sum total of 115 subjects, were blinded. Three of these studied cat immunotherapy, one studied dog, and one studied both cat and dog. Asthmatic subjects were used in each of these trials, and it should be noted that no studies have evaluated patients with rhinitis induced by animal danders. Although the data are still somewhat limited, several conclusions can be drawn. First and foremost, there is general agreement that immunotherapy for both cats and dogs is efficacious. Reactivity as determined by skin tests, inhalation challenge, and conjunctival challenge was reduced by immunotherapy in most studies. The reduction in allergen bronchial challenge sensitivity may have be as little as 2.8-fold 39 or as great as 11-fold. 33 This difference might be of practical significance as three-fold changes would probably mean very little to an individual who lives with a cat, whereas a Ill-fold change might provide some protection. Based on our knowledge of allergen levels in homes, however, even that change might not provide significant protection for patients living in homes that have pets. For example, although we believe that levels of cat allergen in settled dust above 2,000 ng/g may be associated with symptoms, levels of cat allergen in homes with cats are usually above 50,000 ng/g and commonly reach 200,000 ng/g. Thus, patients living with pets may live too far above the threshold of response to benefit significantly from immunotherapy. Unfortunately, although several studies have suggested symptomatic improvement upon animal exposure, few have adequately studied this parameter, particularly in patients living with pets. Furthermore, in the two studies that used a controlled exposure to live cats, one showed no improvement after immunotherapy. 39 and the other showed only a modest delay in the onset of symptoms. 28 We therefore believe, based on the available data, that immunotherapy is most likely to be successful in individuals with intermittent exposure and that it cannot be recommended as a routine for individuals who live with a cat or dog. Second, although some data regarding allergen doses can be taken from these studies (Table 3), the results are somewhat confusing and do not provide an adequate answer about the doses that might be most efficacious. In the studies in which Fel d I was measured, maximum cumulative doses ranged from 64.5 µg to 4.7 mg, apparently with similar efficacy. Maintenance doses ranged widely and are even more confusing. For example, Van Metre 39 attempted to reach a maintenance dose of 4.56 Food and Drug Administration units (21 µg), Bacur 1 used a peak dose of 100,000 biologic units (said to contain 200 µg of Fel d I), and Taylor 35 used a dose of 800 µg. For the studies using square units, 1 sq U was said to contain 43 pg of Fel d I, so that maintenance doses of 100,000 sq U would be expected to contain only 4.3 µg. 33 Bertelson et al 4 suggested that doses of 100,000 sq U for either cats or dogs were likely to be efficacious (five of six subjects), whereas doses less than 80,000 sq U were effective in only two of eight subjects. Finally, these doses would be difficult to attain with many commercially available extracts. Third, conclusions can also be drawn as to the safety of animal dander immunotherapy. The studies suggest that systemic reactions with such therapy are common, especially with cats. This is likely due to the fact that more potent cat extracts, standardized for Fel d I, are available for use. We would therefore recommend that animal dander immunotherapy be undertaken with caution and that it not be used lightly; it clearly should not be added to an extract unless there are strong indications to do so. Reaction rates such as these may even make immunotherapy impractical in some situations.