[Pharmwaste] insights regarding discussion concerning excretion of drugs

[Tenace, Laurie]

All,
Dr. Christian Daughton, EPA researcher, has asked  me to forward his comments on our current discussion on excretion rates. 
Laurie



The current discussion regarding the extent of an API's excretion
unchanged is considerably more complex than might first appear. It's
simply not possible to glean the appropriate information from the
pharmacokinetics (PK) data submitted by clinical trials. This is partly
because the range of values in PK parameters for an individual API can
be quite large (as a function of the variability among people). But most
importantly, these PK data do not take into account the various chemical
forms in which an API is excreted - particularly in the form of
conjugates, such as glucuronides. For assessing the potential for
subsequent environmental exposure, the extent of conjugate excretion is
essential since the conjugates can be subsequently hydrolyzed (e.g.,
primarily by bacteria in sewage) to reform the parent API. Many APIs are
extensively excreted not necessarily in unchanged form, but as
conjugates.

The topic of modeling disposal's contributions of APIs to the
environment (via sewers) is discussed for the first time in a paper
published in December. Although the focus of this paper is on the
special case of dermal medications, the same principles apply to all
medications.
      Daughton CG and Ruhoy IS. "Environmental Footprint of
Pharmaceuticals: The Significance of Factors Beyond Direct Excretion to
Sewers," Environmental Toxicology & Chemistry 2009, 28(12):2495-2521;
doi:10.1897/08-382.1; available:
http://www3.interscience.wiley.com/cgi-bin/fulltext/123234136/PDFSTART