Transdermal iontophoresis and skin retention of piroxicam from gels containing piroxicam:: Hydroxypropyl-β-cyclodextrin complexes

Iontophoretic transport of piroxicam (Px) across porcine ear skin in vitro was investigated. Cathodal iontophoresis of negatively charged Px was carried out from gel formulations containing Px as an inclusion complex with hydroxypropyl-beta -cyclodextrin (HP-beta -CD). From the gels, following a 7 h application period at 0.4 mA/cm(2), iontophoresis delivered 3.4 times more drug than passive diffusion. The formation of Px: HP-beta -CD complexes did not increase the iontophoretic Px flux through the skin. However, Px complexation with HP-beta -CD allowed us to increase the drug concentration in the gel; because of that, the amount of Px transported across the skin increased considerably. After iontophoretic experiments, the amount of Px retained in skin seemed to be related to the flux values obtained in each case. Skin pretreatment with 20% HP-beta -CD, tested passively and iontophoretically for 3h, followed by the application of gel containing Px:HP-beta -CD complexes, showed no enhancing capacity, in any case. The amount of Px retained in the skin after pretreatment experiments was found to be very similar to that obtained without skin pretreatment and was observed to be related to the Px flux through the skin.