Figure 8. Thermal cycling study for packaged dry LT patches. Conditions were modeled for products targeting both refrigerated and room temperature storage. The temperature cycling regiment is listed in the table. LT was extracted from patches and quantified by SE-HPLC (top panel) and assessed for potency by Y-1 cell assay (bottom panel). SE-HPLC results are reported as the LT percent of the label claim and are the average of 3 patches. Potency results are reported as log, μg-1. Four control groups held at a constant temperature for the study duration were run. HPLC and Y-1 results from thermal cycled samples were not significantly different from those reported for control samples kept at 2-8 °C (as determined by student t-test, data not shown).

Water Activity of The Dry Patch

Water activity, rather than moisture content, is used commonly by microbiologists and food technologists to assess criteria for safety and quality of food products.^21–23 Water activity, a_w, measures the free water in a product (i.e., in our case, the dry LT patch); whereas, moisture content measures both free and bound water. According to USP <1112>,²⁴ when the water activity of a product decreases below 0.60, microorganisms cannot obtain the water necessary to support their growth. Most bacterial growth is inhibited below a_w~0.91; most yeasts cease growing below a_w=0.87, and most molds do not grow below a_w=0.80. The a_w of the dry IS patch was determined by LabMaster-aw (manufactured by Novasina Instruments) and found to be around 0.35±.03, which is significantly lower than the absolute limit of microbial growth of a_w=0.60. Thus, the dry IS patch formulation will not support microbial growth during storage in a nitrogen-purged sealed foil pouch.