Figure 8 also shows the results of the thermal cycling study as measured by the SE-HPLC content assay (top panel) and Y-1
cell potency assay (bottom panel). After 12 days of thermal cycling between -20 and 25 ºC and -20 and 40 ºC, the averaged
data shows no statistically significant decrease in Y-1 cell potency or LT content in the patches. The results of this study
suggest the possible use of expanded shipping conditions for this product (beyond 2–8 ºC).
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, aw, 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 aw~0.91; most yeasts cease growing below aw=0.87, and most molds do not grow below aw=0.80. The aw 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 aw=0.60. Thus, the dry IS patch formulation will not support microbial growth during storage in a nitrogen-purged sealed foil