Sweat-tainted drugs may also explain the emergence of some antibiotic resistance, researchers say.

By Janet Raloff

Web edition: April 2, 2010

SAN FRANCISCO Traces of over-the-counter and prescription meds taint the environment. The presumption  ̶  and it's a good one  ̶  has been that most of these residues come from the urine and solid wastes excreted by treated patients. But in some instances, a leading source of a drug may be skin  ̶  either because the medicine was applied there or because people sweat it out.

When either occurs, patients risk not only polluting the outdoor environment  ̶  via sewer inputs from showers and laundering  ̶  but also exposing their homes and families. Or so explained physician Ilene Ruhoy of the Touro University College of Osteopathic Medicine in Henderson, Nev., last week, at the American Chemical Society spring national meeting.

Ruhoy reviewed calculations that she and Christian Daughton of the Environmental Protection Agency in Las Vegas made after poring over 177 papers for an encyclopedic, 27-page analysis that they published in Environmental Toxicology and Chemistry, last December. It was part of a special issue on the chemistry of pharmaceutical and personal-care products (like hand creams, shampoos and deodorants) in the environment.

Until now, Ruhoy and Daughton pointed out, “no formal discussion has ever been presented, to the best of our knowledge,” on bathing, laundering or trash as a polluting source of drugs  ̶  including those, like drug-delivery skin patches, which may contain 95 percent or more of the original dose in the “used” patch. (The reason: Drug delivery via this route is so inefficient that manufacturers load up their patches with a whopping excess of a medication  ̶  much of which still remains in the patch when it’s ready for disposal.)

Science News readers will have encountered these ideas, including the risk of environmental contamination from very-polluting used drug patches. But the sweat angle: That’s new.

Not to pharmacologists, of course. Some of them have been reporting for decades that health care workers can encounter substantial exposures to chemotherapy drugs and other pharmaceuticals while washing patients’ clothes and bedding. I’ve included a few cites to such papers accompanying this blog. But the concern in those papers has been potential risks to workers’ health. As Ruhoy and Daughton point out in their new analysis, family members and friends remain a largely ignored  ̶  and therefore uninformed  ̶  population that may also be at risk of coming into dangerous contact with sweated-out pharmaceuticals or skin-applied drugs.

How big an environmental risk skin may pose depends on the drug, how it’s administered and how the body does or doesn’t break it down. Within an hour of being administered, pharmaceuticals may begin escaping in sweat, the researchers note, and continue to do so for days to weeks. In many cases, only 1 to 2 percent of ingested drugs will be released this way. Small potatoes.

But there are exceptions. Ruhoy and Daughton used published data from one 2008 paper and calculated that up to 47 percent of a 600 microgram daily dose of the powerful opiate pain killer fentanyl could be excreted in sweat. To people who have not built up a tolerance to this drug, sweat’s release could be lethal  ̶  if they got enough at one time. (Clearly, my miniature dachshund could. He licks any arms, legs, and feet in tongue’s reach  ̶  and does so every chance he gets.)

Considering how little of this drug typically gets excreted via urine, the amount of sweat-released drug available for washing off and down the drain could be six times as much as would enter water from urine and feces sent down a toilet. And while much of any sweaty outpouring would undoubtedly end up absorbed by clothing or bedding, sweaty palms could leave residues on door knobs, faucet handles, book jackets, TV remotes, kitchen counters and sandwiches made for the kids. Or be transferred through a handshake. Or to a family member who holds the arms of an unsteady patient.

The researchers also described antiobiotics-tainted sweat “as a possible major means of quickly promoting and spreading resistance.” They cited papers that documented the excretion of antibiotics through skin and argue that this might “be an overlooked cause of transmission of multiresistance among bacteria in hospitals and other care facilities that routinely administer antibiotics.”