Common confounders of dietary elimination trials contain the antigens soy, pork, and beef.

Nutritionists and dermatologists recommend avoiding flavored over-the-counter (OTC) products and medications during dietary elimination trials because those products are thought to contain common proteins that may confound the trial. The objective of this study was to determine if there are soy, pork, and beef antigens in flavored OTC products and medications and, if so, could those antigens be identified. Seven products, three OTC products and four veterinary therapeutics, were tested using enzyme-linked immunosorbent assays (ELISA) for the presence of soy, pork, and beef antigens, in addition to positive and negative controls. All OTC test products produced ELISA results in agreement with their ingredient lists. ELISA testing of veterinary therapeutic products did not agree with either their ingredient lists or product inserts because of other ingredients not listed. Veterinarians should contact manufacturers of oral therapeutics prior to prescribing them to determine other ingredients. Likewise, manufacturers should be contacted regarding "natural and artificial flavors." Lastly, gelatin capsules may contain either beef or pork proteins and should not be administered during a trial. In conclusion, flavored medications contain the common antigens soy, pork, and beef although they may or may not be listed on the ingredient list or product insert.