1: Pharm Res. 2007 Oct;24(10):1897-901. Epub 2007 May 12.

Assessment of the "skin reservoir" of urea by confocal Raman microspectroscopy
and reverse iontophoresis in vivo.

Wascotte V, Caspers P, de Sterke J, Jadoul M, Guy RH, Préat V.

Unité de Pharmacie Galénique, Université Catholique de Louvain, Avenue E.
Mounier, UCL 7320, 1200, Brussels, Belgium.

PURPOSE: To demonstrate the "skin reservoir" of urea by confocal Raman
microspectroscopy in vivo and to evaluate its impact on the non-invasive
monitoring of the analyte by reverse iontophoresis. METHODS: Urea was extracted
iontophoretically over a 2-h period across the skin of adult volunteers and
patients with chronic kidney disease. Confocal Raman microspectroscopic profiles 
of skin were recorded before and after 30 min of current application. RESULTS:
Urea extraction was higher at the beginning of current passage, but then
decreased to achieve stable values after 2 h of iontophoresis. After 30 min of
iontophoresis, the Raman spectra highlighted a clear depletion of urea at the
surface of the skin. Lactate distribution was also modified both at the surface
and deeper into the skin. CONCLUSIONS: A source of urea in the skin, unrelated to
the concentration circulating in the blood, was strongly suggested by extracted
urea flux observed over time and by the Raman spectroscopy. This "urea reservoir"
must be removed before systemic urea levels can be non-invasively monitored by
reverse iontophoresis.

PMID: 17497081 [PubMed - in process]

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