Sweat has been identified as a helpful matrix to detect the presence of drugs and other analytes, such as chloride while testing cystic fibrosis. The Sweat Patch, which is like a bandage, is worn to collect the sweat and continuously monitor the usage of drugs, lasting for almost 1 week. Hence, drug detection can be done a number of times between few months for hair and between few days for urine. ‘Sweat Patch’ is basically a device called ‘PharmChekTM’, a trademark that is manufactured by a pharmaceutical company named PharmChem. We are only aware of the sweat patch which is available commercially, however, many different techniques have been used to collect sweat, such as; using capillary tubes to collect liquid sweat, using occlusive absorbent dressings and the simple skin wiping and blotting technique. In order to collect sweat, its production is stimulated chemically using ‘Pilocarpine’, where iontophoresis is electrically stimulated before heating. No external or additional stimulation is required when using the sweat patch as the regular sweat secretions are easily absorbed into the sweat patch while it is being used.
FIGURE 8-1 The PharmCheckTM Sweat Patch.
The figure 8-1 above shows the components of a sweat patch which includes a 3 x 5 cm inner collection pad which is a cellulosic absorbent, a polyurethane gas permeable outer membrane (used in dressing wounds) and adhesive for adherence to the skin which is normally a hypoallergenic. The outer membrane is specially designed to permit tiny molecules, like water vapors, through the patch while the larger molecules, such as drugs, are held back. The absorbent pad collects the excreted drugs and their metabolites, which are held back by the outer membrane during the week in which the sweat patch is used. The user of the patch then removes the pad and submits it for testing and analysis which is done using chromatographic and conventional immunoassay methods.
The criminal justice system largely uses the sweat patch in programs designed for drug-treatment and it is also by the Federal Courts of US. The Substance Abuse and Mental Health Services Administration (SAMHSA) published some guidelines in “Proposed Revisions to Mandatory Guidelines for Federal Workplace Drug Testing Programs” proposing the use of Sweat Patch in federal workplace testing programs. However, the patch is less likely to be commonly used due to its continuous monitoring, except for ‘last chance agreements’ due to a previous drug test result being positive.