Improving the Pharmcheck Sweat Patch: Reducing False Positives from Environmental Contamination and Increasing Drug Detection

Drugs externally applied to human skin were shown to bind readily. Drugs deposited on the skin of drug-free volunteers several days prior to application of the sweat patch were not completely removed by normal hygiene or the cleaning procedures recommended commercially before application of the sweat patch. These externally applied drugs cause false positives for drug-free volunteers did not use drugs. We term this mode of contamination-Contamination From Within CFWI. A number of different cleaning procedures were used to remove externally applied drugs. Orange Pumice hand cleaner followed by water and then isopropanol substantially reduced CFWI. However, even with these extensive cleaning procedures, some drugs remained, which could cause false positives. We propose saving the ispropanol cleaning swabs and testing the retained swabs for drugs, if the wearer of the patch denied drug use. We also propose that a ratio 10 of the drugs in the cleaning pads to that found in the patch is indicative of CFWI. A lower ratio or drug-free cleaning pads would indicate drug use by the individual. Heavy sweating facilitates drug transfer. However, not all drugs placed on the skin arc transferred to the patch. The presence of glycerol in the absorptive pad increases transfer 3-6 fold.