Monoclonal antibody-standardized cat extract immunotherapy: risk-benefit effects from a double-blind placebo study

Twenty-eight patients (14 in an active treatment group and 14 in a placebo group) with rhinoconjunctivitis and asthma caused by cat hypersensitivity took part in a placebo-controlled, randomized, double-blind study to evaluate the risk-benefit quotient of the maintenance dose corresponding to 13.2 micrograms Fel d I antigen. The cat extract was biologically standardized and quantified with monoclonal antibodies (100 biological units: 33 microgram of Fel d I antigen, 650 micrograms of albumin, and 99 micrograms of Fel d Bd/K30 antigen). After 1 year of treatment, the systemic reactions to cat extract immunotherapy were mild and infrequent. Improvement was observed in the active treatment group in comparison with the placebo group in the medication-symptoms score (p < 0.001); in skin prick test (p < 0.001), conjunctival provocation test (p < 0.001), and allergen bronchoprovocation test (p < 0.05) results, and in nonspecific bronchial hyperreactivity measured with methacholine, which was not statistically significant. This study demonstrates the favorable risk-benefit quotient of the dose of 13.2 micrograms of Fel d I antigen, which may serve as a future reference in defining the optimum dose and appropriate proportion of antigens that should be administered in cat extract immunotherapy.