Percutaneously insertable catheter (10) for administering an active agent to a body site, the catheter comprising: - a distal portion (22) expandable from a contracted introduction condition to a deployed administration condition, to stabilize the distal end (2) of the catheter (10) at said body site, and - a flexible tubular element (16) coupled to said distal end (2) of the catheter (10) to receive the active agent and administer it to said body site, characterized in that: - the flexible element (16) comprises an outer tubular element (161) and an inner tubular element (167) inserted in the outer tubular element (161), one (161) having between said outer tubular element (161) and said element inner tubular (167) notches (163) that allow the spine-like curvature of the flexible element (16) towards said body site, and - the other (167) between said outer tubular element (161) and di The inner tubular element (167) forms a flexible sealing closure covering of the notches (163) present in one (161) of said outer tubular element (161) and said inner tubular element (167).Catéter insertable percutáneamente (10) para administrar un agente activo a un sitio del cuerpo, comprendiendo el catéter: - una parte distal (22) expandible desde una condición contraída de introducción hasta una condición desplegada de administración, para estabilizar el extremo distal (2) del catéter (10) en dicho sitio del cuerpo, y - un elemento tubular flexible (16) acoplado a dicho extremo distal (2) del catéter (10) para recibir el agente activo y administrarlo a dicho sitio del cuerpo, caracterizado por que: - el elemento flexible (16) comprende un elemento tubular exterior (161) y un elemento tubular interior (167) insertado en el elemento tubular exterior (161), presentando uno (161) de entre dicho elemento tubular exterior (161) y dicho elemento tubular interior (167) unas muescas (163) que permiten la curvatura a modo de columna vertebral del elemento flexible (16) hacia dicho sitio del
