An introducer assembly kit usable in either an over-the-wire mode or rapid exchange mode, including: a catheter having a proximal end disposed at a proximal location of the introducer assembly, a distal end extending to a distal tip of the introducer assembly, and an outer catheter wall; the catheter including: (i) a medical device holding portion proximate the distal end thereof, (ii) a guide wire lumen extending between the proximal and distal ends to allow use in over-the-wire mode, a fluid supply coupling to the guide wire lumen being provided at the proximal end of the catheter; and (iii) a side opening extending through the outer wall to the guide wire lumen between a proximal portion of the guide wire lumen and a distal portion of the guide wire lumen, wherein the side opening and the guide wire lumen are in use simultaneously open, the guide wire lumen and side opening being able to receive a guide wire therethrough for use in rapid exchange mode; the catheter being flexible at least in the location of the side opening; a source of fluid agent including a fluid source coupling configured to couple to the fluid supply coupling of the catheter and thereby to couple a supply of fluid agent to the guide wire lumen; whereby the assembly is configurable to dispose the guide wire through the side opening and in the distal portion of the guide wire lumen in use in rapid exchange mode, and to dispense fluid agent through the proximal portion of the guide wire lumen from the proximal end of the catheter, whereby when the guide wire is disposed in the distal portion of the guide wire lumen in rapid exchange mode the guide wire impedes passage of fluid agent through the distal portion of the guide wire lumen such that fluid agent from the proximal portion of the guide wire lumen exits the catheter at the side opening through which the guide wire is disposed. a catheter having a proximal end disposed at a proximal location of the introducer assembly, a distal end extending to a distal tip of the introducer assembly, and an outer catheter wall; the catheter including: (i) a medical device holding portion proximate the distal end thereof, (ii) a guide wire lumen extending between the proximal and distal ends to allow use in over-the-wire mode, a fluid supply coupling to the guide wire lumen being provided at the proximal end of the catheter; and (iii) a side opening extending through the outer wall to the guide wire lumen between a proximal portion of the guide wire lumen and a distal portion of the guide wire lumen, (i) a medical device holding portion proximate the distal end thereof, (ii) a guide wire lumen extending between the proximal and distal ends to allow use in over-the-wire mode, a fluid supply coupling to the guide wire lumen being provided at the proximal end of the catheter; and (iii) a side opening extending through the outer wall to the guide wire lumen between a proximal portion of the guide wire lumen and a distal portion of the guide wire lumen, wherein the side opening and the guide wire lumen are in use simultaneously open, the guide wire lumen and side opening being able to receive a guide wire therethrough for use in rapid exchange mode; the catheter being flexible at least in the location of the side opening; a source of fluid agent including a fluid source coupling configured to couple to the fluid supply coupling of the catheter and thereby to couple a supply of fluid agent to the guide wire lumen; whereby the assembly is configurable to dispose the guide wire through the side opening and in the distal portion of the guide wire lumen in use in rapid exchange mode, and to dispense fluid agent through the proximal portion of the guide wire lumen from the proximal end of the catheter, whereby when the guide wire is disposed in the distal portion of the guide wire lumen in rapid exchange mode the guide wire impedes passage of fluid agent through the distal portion of the guide wire lumen such that fluid agent from the proximal portion of the guide wire lumen exits the catheter at the side opening through which the guide wire is disposed.