Technical / FAQ

The absorption pad within the patch is protected from the environment by a layer of film composed of polyurethane coated with adhesive. The polyurethane film is a
"semi-permeable membrane,” which allows the transfer of water vapor and gases. Studies involving this concern were conducted by applying drugs to the exterior of the patch and subsequently collecting and analyzing the absorption pad. No drugs were found in these experiments.

Any “normal” constituents of sweat do not produce positive results. While drugs may be present in the environment, and even possibly present on skin surfaces, studies have not demonstrated (in realistic scenarios) that the transfer of such environmental drugs into sweat patches worn by these individuals would result in a positive analysis.

PharmChem's contract laboratory employs procedures substantially equivalent to those required by SAMHSA for urine testing. Years of experience with these procedures have shown a negligible problem with false positives. As an additional safeguard, the laboratory utilizes blind quality assurance samples in the testing process.

Detection periods for the PharmChek® sweat patch must be thought about in terms that are a bit different from urine testing. The PharmChek® patch is a collection device designed to retain evidence of drug use for an extended period of time. That means that drugs excreted through sweat because of drug use at any time during the wearing of the patch will be collected, retained, and detected during analysis. For example: a PharmChek® patch were worn for 7 days it might be positive because of drug use on Day 1 or on Day 6.

Drugs and drug metabolites are excreted through bodily fluids over the course of about 48-72 hours. Therefore, if a subject used drugs yesterday and the PharmChek® patch is applied today, the subject's body is still excreting that drug out of their system when the patch is applied. This would result in a positive confirmation if both the parent drug and the metabolite are detected at or above the cut-off level at screening and confirmation.

Clinical trial data from the administration of known amounts of drugs show that essentially all of the drugs detectable with the patch are excreted over a period of about 2 - 3 days. This is quite similar to the elimination period for drugs in urine. The difference is that the PharmChek® patch is constantly sampling the sweat and retaining all evidence of drug use.

Data from clinical trials show that patches worn at least 24 hours after drug use can reliably test for that drug.

Solvents, such as chloroform or acetone, have been applied to the covering of the PharmChek® patch. They bubble and shrivel the PharmChek® covering and evidence of adulteration is easily identified.

In order to adulterate the PharmChek® patch a substance must penetrate the outside covering of the patch. The only feasible method is to inject substances into the PharmChek® pad with a hypodermic needle. Part of the removal process for the patch includes checking for the following:

1) Is a chemical odor observed?

2) Are any holes observed in the film, when held to the light?

3) Is any redness observed under the pad?

4) Is the pad discolored?

The skin has approximately 15 to 20 layers of skin cells. The top layer of cells is constantly being shed. How long a person can wear a PharmChek® Sweat Patch is determined by how long it takes for enough skin cells to be shed that the adhesive coating no longer sticks to the subject’s body.

The length of time varies from person-to-person and skin type to skin type. From our wear tests we have determined that most clients can successfully wear the patch for at least 10 days. There are no known health concerns associated with wearing PharmChek® for periods longer than 10-14 days, provided the skin around and under the patch appears healthy and blemish-free.