Validity of anti-reflux formulas as a slightly thick liquid: effect of time, caloric density, and refrigerated storage on formula thickness

Background: Advancements in neonatal medicine have resulted in an increased prevalence of infants suffering from swallowing deficits. One method to treat these deficits is to provide thickened liquids through the use of anti-reflux formulas. However, little is known regarding the impact of common clinical conditions such as time since mixing, caloric density, and refrigeration on the thickness of these anti-reflux formulas. The aim of the investigation was to test the effect of clinical variables on thickness of two commonly used U.S. anti-reflux formulas (Enfamil A.R.™ and Similac Spit-Up ® ) in their ready to feed and powder formulations. Methods: Thickness of two anti-reflux formulas (Enfamil A.R.™ and Similac Spit-Up ® ) was tested in their 20 kcal/oz ready to feed formulation and at graduated caloric densities of their powder formulations (20–30 kcal/oz). Thickness was determined using International Dysphagia Diet Standardization Initiative (IDDSI) flow testing methodology and quantified as residual volume and thickness category (thin, slightly thick, mildly thick, moderately thick). Repeated-measures and two-way ANOVA was used to test the effect of formula variables on thickness. Results: Time after mixing did not impact thickness of 20 kcal/oz ready to feed formulations (Enfamil A.R.™, slightly thick, 1.3, 1.1–1.5 mL) (Similac Spit-Up ® , thin, 0.7, 0.4–0.8 mL) though it did for Enfamil A.R.™ powder formulations as characterized by an increase in thickness from thin to slightly thick over 30 minutes. Increasing caloric density of Enfamil A.R.™ caused a stepwise increase in thickness, with thicknesses ranging from slightly thick to moderately thick at the end of the 30-minute testing period across 20–30 kcal/oz formulations. Similac Spit-Up ® did not exhibit any change in thickness based on caloric density. Both Enfamil A.R.™ and Similac Spit-Up ® showed non-significant trends of increased thickness when tested cold after three hours of refrigeration, followed by thinning close to baseline values once the formula was re-heated. Conclusions: Although Enfamil A.R.™ is a valid slightly thick liquid option in its ready to feed formulation, the validity of its powder formulation to reach slightly thick designation is dependent on its caloric density. Future investigations examining the safety of this practice are warranted.