Objectives: We conducted a prospective, randomized study to evaluate the cumulative incidence of allergy or other adverse reactions to soy formula and to extensively hydrolyzed formula up to the age of 2 years in infants with confirmed cow's milk allergy.
Study design: Infants (n = 170) with documented cow's milk allergy were randomly assigned to receive either a soy formula or an extensively hydrolyzed formula. If it was suspected that the formula caused symptoms, a double-blind, placebo-controlled challenge (DBPCFC) with the formula was performed. The children were followed to the age of 2 years, and soy-specific immunoglobulin E antibodies were measured at the time of diagnosis and at the ages of 1 and 2 years.
Results: An adverse reaction to the formula was confirmed by challenge in 8 patients (10%; 95% confidence interval, 4.4%-18.8%) randomly assigned to soy formula and in 2 patients (2.2%; 95% confidence interval, 0.3% to 7.8%) randomly assigned to extensively hydrolyzed formula. Adverse reactions to soy were similar in IgE-associated and non-IgE-associated cow's milk allergy (11% and 9%, respectively). IgE to soy was detected in only 2 infants with an adverse reaction to soy. Adverse reactions to soy formula were more common in younger (<6 months) than in older (6 to 12 months) infants (5 of 20 vs 3 of 60, respectively, P =.01).
Conclusions: Soy formula was well tolerated by most infants with IgE-associated and non-IgE-associated cow's milk allergy. Development of IgE-associated allergy to soy was rare. Soy formula can be recommended as a first-choice alternative for infants >or=6 months of age with cow's milk allergy.