A transdermal medicament patch includes a biocompatible substrate having a therapeutic face on one side configured for disposition against the skin of a patient, a biocompatible adhesive on the therapeutic face, a planar medicament matrix covering a portion of the therapeutic face, and a release liner covering the portion of therapeutic that is not obscured by the medicament matrix. An aperture formed through the release sheet affords direct access by medicament to the entire surface of the medicament matrix opposite from the therapeutic face of the substrate. An active electrode positioned between the medicament matrix and the therapeutic face of the substrate includes an electrically conductive backing layer positioned against the therapeutic face of the substrate and a pH-control layer covering less than all of the side of the backing layer opposite from the therapeutic face of the substrate. One active electrode design criterion relates the relative size of the pH-control layer to the size of the backing layer； another relates the size of portion of the area of the backing layer that is free of the pH-control lawyer to the size of the pH-control layer. The pH-control layer is made of an electrically conductive material capable of moderating changes in the hydrogen-ion concentration in the medicament matrix during iontophoretic current flow. An electrical contact electrically coupled through the substrate to the backing layer includes a hollow, electrically conductive snap fitting having an open end and a cooperating stud that is inserted into the open end of the snap.
