Clinical efficacy of specific immunotherapy to cat dander: a double-blind placebo-controlled trial

To assess the efficacy of specific immunotherapy with standardized cat dander extract, using objective endpoints and simulated 'natural' exposure to cats.

Double-blind, randomized, placebo-controlled study carried out at a UK Allergy research clinic.

Twenty-eight patients with moderate to severe allergic rhinoconjunctivitis with asthma due to cat allergy. Subjects were stratified for cat sensitivity, cat ownership and asthma, and the groups were well matched for all relevant parameters.

Symptom scores and peak flow rate during and after exposure to cats in a cat-room. Skin tests and conjunctival provocation thresholds.

The actively treated group showed a marked reduction in symptoms during the cat exposure (mean score 61.6-17.1; P < 0.001) with no change in the placebo group (64.7 vs 62.1). The active group also showed a reduced peak flow response to cat exposure (mean fall of 85 L/min pretreatment, 29 L/min after treatment, P < 0.005) as well as reductions in conjunctival provocation sensitivity, skin sensitivity to cat extract and skin sensitivity to house dust mite (D.pteronyssinus). Skin reactivity to histamine and codeine were unaltered. No significant adverse reactions were encountered.

Specific immunotherapy seems to be an effective treatment for cat allergy. Allergy to cats is common and often poorly controlled on conventional pharmacotherapy. Although cat allergy has not traditionally been considered as a valid indication for immunotherapy in the UK, it should now be considered as a legitimate treatment, especially for those who are unable to avoid exposure.