A method for delivering a therapeutic substance to a treatment site within a body lumen includes advancing a balloon catheter to the treatment site. A balloon of the balloon catheter is inflated and while the balloon is inflated, a primer that coats the treatment site and attracts the therapeutic substance thereto is delivered through a first fluid delivery lumen of the balloon catheter. The balloon of the balloon catheter is deflated for a predetermined period of time. The balloon of the balloon catheter is reinflated and while the balloon is reinflated, the therapeutic substance is delivered through a second fluid delivery lumen of the balloon catheter. The primer improves adherence of the therapeutic substance to the treatment site.