Comment: This investigation is the first in vivo study of transdermal iontophoresis on fentanyl and sufentanil pharmacokinetics coupled with acute nociceptive properties. However, because iontophoresis was applied for only 1 hr, steady-state plasma levels were not attained, making it impossible to compare the results with transdermal fentanyl and sufentanil delivery systems not dependent on iontophoresis. Also, there is no mention of the number of animals included in the study, the mode of evaluation, and the number of blood samples collected. Therefore, one should be cautious in extrapolating these results to humans