Disclosed are methods of selectively delivering a medicant to an abnormal brain region and/or to a malignant tumor in a mammalian subject, including a human. A medicant is administered simultaneously or substantially simultaneously with a potassium channel agonist (other than bradykinin or a bradykinin analog), such as NS-1619,1-EBIO, a guanylyl cyclase activator, a guanylyl cyclase activating protein, minoxidil, pinacidil, cromakalim, or levcromakalim, whereby the medicant is delivered selectively to the cells of the abnormal brain region and/or to the tumor, compared to normal tissues. Thus, among the disclosures is a method of treating a malignant tumor in a human subject. Also disclosed are pharmaceutical compositions that combine a potassium channel agonist together with a medicant and a kit for enhancing the delivery of a medicant to an abnormal brain region and/or to a malignant tumor.