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Technical Q&A


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Reliability/False Positives

 
Will "passive" or inadvertent  environmental exposure to a drug cause a positive test result?
We studied this question directly, even though there is a strong theoretical reason not to believe in such possibility. The absorption pad of 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.  Initial 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.
 
Subsequent experiments have involved variations of these initial experiments and have incorporated such variations as wetting the absorbent pad with various solutions and buffers, varying the pH of the of the solution containing drugs that was applied to the exterior of the polyurethane membrane, and varying the temperature and time that the varying solutions are allowed to sit or incubate on the exterior of the polyurethane membrane.
 
These studies have demonstrated that when both the inside and the outside of the patch were dry, no drug transfer could be noted.  Under certain conditions, the outer polyurethane membrane can be altered and made permeable to the diffusion of applied drugs onto the absorption pad.  However these conditions are not what one would realistically expect to encounter in real world situations.
 
Will the
PharmChek® patch be positive if the target drug is not taken?
This question was addressed directly in clinical trials by applying patches to self-reported non-users. The drugs that were tested for were not found in patches from non-users. From this we conclude that any “normal” constituents of sweat do not produce positive results.
 
In addition, while drugs may be present in the environment in certain situations and even possibly present on skin surfaces, none of these studies has demonstrated in realistic scenarios that the transfer of such environmental drugs into patches worn by those individuals present in these environments.
 
Will drugs other than the target drugs produce false positives?
This is not directly addressed in our studies - but was also not thought by FDA to be necessary.  The testing procedure that was cleared by the FDA requires GCMS confirmation testing of initial immunoassay test positives. This is the same procedure required by SAMHSA (formerly NIDA) in the testing of urine samples. GCMS (and its successor LC/MS/MS) confirmation is scientifically capable of distinguishing the target drug from other drugs that might be present in sweat, preventing false positives.
 
A second important point is that "parent" drugs, rather than just drug metabolites, are found in sweat after drug use.  "Parent" drug is the same chemical compound that was taken by the drug user (example, heroin). Drug metabolites are "breakdown products" of the parent drug.  Many drugs such as codeine and heroin produce the same metabolites in urine, so a urine test cannot reliably distinguish between them. Because sweat contains both the parent drug and the metabolites, the test can tell which drug has been taken.
 
Is the laboratory process subject to false-positive error?
Clinical Reference Laboratory will be employing procedures substantially equivalent to those required by SAMHSA for urine testing.  Years of experience with these procedures have demonstrated that there is a negligible problem with false positives.  As an additional safeguard, Clinical Reference Laboratory utilizes blind quality assurance samples in the testing process.

Detection Periods
 
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.  If a PharmChek® patch were worn for 7 days, for example, it might be positive because of drug use on Day 1 or on Day 6.
 

How long does it take for drugs to be excreted through sweat after a single drug use?
Clinical trial data from the administration of known amounts of drug 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.
 
How long after use must the
PharmChek® patch be worn in order to produce a positive result?
Data from clinical trials show that patches worn at least 24 hours after drug use can reliably test for that drug.
 
Adulterants
 
Solvents, such as chloroform or acetone, have been applied to the covering of the
PharmChek® patch.  They bubble and shrivel the PharmChek® patch covering and evidence of trying to tamper with these chemicals would be very easily noticed.
 
In order to adulterate the
PharmChek® patch a substance would have to penetrate the outside covering of the patch.  The only feasible method that has been tried is to inject substances into the PharmChek® patch with a hypodermic needle.  Part of the removal process for the patch includes holding the outside cover of the used PharmChek® patch to the light to see if there are signs of needle holes.
 
 
PharmChek Wear Period
 
How long can a person wear the
PharmChek® Drugs of Abuse Patch?
The skin has between 15 to 20 layers of skin cells.  The top layer of cells is constantly being shed.  The factor that determines how long a person can wear a
PharmChek® patch is how long it takes for enough skin cells to be shed that the adhesive coating on the patch is completely covered with skin cells and can no longer stick to testing subject’s body.
 
This length of time varies between person-to-person and skin type to skin type.  From our wear tests we have observed that most people can wear the patch for 7 to 10 days.  The Michigan Pilot Study showed 87% of the people who wore the patch could wear it for 14 days.  There is no known consistent health concerns associated with wearing the
PharmChek® patch for periods longer than 14 days if the skin around and under the PharmChek® patch appears healthy and blemish-free.

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