Clinical response to 2 commonly used switch formulas occurs within 1 day.

Very fussy or extremely fussy infants were randomized to receive: soy-based formula (Soy: n = 82) or a partially hydrolyzed cow's milk protein (CMP), low-lactose formula (PHF: n = 77) in a multicenter, double-blind, randomized, parallel, prospective 28-day feeding trial. Body weight and infant formula tolerance were reported. Adverse events were recorded throughout the study. A significant reduction in mean scores of fussiness, gas, spit-up, and crying compared with baseline measures was observed in infants who received either Soy or PHF within 1 day of formula intake; improvement in symptoms was sustained by study end. Stool consistency remained constant through day 28 in the PHF group, whereas stools in the Soy group became more firm by day 2 and did not return to prestudy consistency. PHF, with a protein profile patterned more closely on human breast milk, improved symptoms of formula intolerance as well as soy-based formula.