An anchor device for securing the position of a medical instrument, the anchor device comprising: a retainer body comprising a first body portion that is pivotably coupled to a second body portion about a longitudinal fold axis, one or more anchor engagement portions being configured to releasably receive one or more corresponding apertures defined by a hub (22, 322) of a catheter, characterized in that a flexible web portion is positioned generally centrally between the first and second body portions and extending longitudinally from the distal end of the retainer body to a proximal face of the retainer body, wherein the flexible web portion is configured to define the longitudinal fold axis, wherein the first body portion and the second body portion include first and second tabs, respectively, at a proximal end of the retainer body, wherein the first and second tabs define a cutout region therebetween to provide visualization and access to a surface under the retainer body; and first and second anchors that extend distally from a distal end of the retainer body, each anchor comprising a flexible tine that is deployable in a subcutaneous region to secure the retainer body relative to a penetration point, the first anchor being coupled to the first body portion and the second anchor being coupled to the second body portion, wherein the first body portion of the retainer body is pivotable relative to the second body portion about the longitudinal fold axis so that the first and second anchors are adjustable from a first configuration in which the flexible tines extend outwardly away from one another to a second configuration in which the flexible tines extend in the same direction. a retainer body comprising a first body portion that is pivotably coupled to a second body portion about a longitudinal fold axis, one or more anchor engagement portions being configured to releasably receive one or more corresponding apertures defined by a hub (22, 322) of a catheter, characterized in that a flexible web portion is positioned generally centrally between the first and second body portions and extending longitudinally from the distal end of the retainer body to a proximal face of the retainer body, wherein the flexible web portion is configured to define the longitudinal fold axis, a first body portion that is pivotably coupled to a second body portion about a longitudinal fold axis, one or more anchor engagement portions being configured to releasably receive one or more corresponding apertures defined by a hub (22, 322) of a catheter, characterized in that a flexible web portion is positioned generally centrally between the first and second body portions and extending longitudinally from the distal end of the retainer body to a proximal face of the retainer body, wherein the flexible web portion is configured to define the longitudinal fold axis, wherein the first body portion and the second body portion include first and second tabs, respectively, at a proximal end of the retainer body, wherein the first and second tabs define a cutout region therebetween to provide visualization and access to a surface under the retainer body; and first and second anchors that extend distally from a distal end of the retainer body, each anchor comprising a flexible tine that is deployable in a subcutaneous region to secure the retainer body relative to a penetration point, the first anchor being coupled to the first body portion and the second anchor being coupled to the second body portion, wherein the first body portion of the retainer body is pivotable relative to the second body portion about the longitudinal fold axis so that the first and second anchors are adjustable from a first configuration in which the flexible tines extend outwardly away from one another to a second configuration in which the flexible tines extend in the same direction.