Injection monitoring module

Injection monitoring module adapted and configured to be removably mounted to a proximal extremity of an injection pen system for delivery of a drug, the injection pen system having a pen body, a proximally located dose setting wheel connected to said body, and an injection activator, the dose setting wheel being rotatable about a central longitudinal axis of the pen injection system during dose setting and fixed against rotation during injection, wherein the injection monitoring module comprises:

• a hollow main body adapted and configured to be coaxially mounted around the body of the pen injection system, the hollow main body comprising a central longitudinal bore having a proximal extremity and a distal extremity, and a central longitudinal axis;
• a magnetic field production means, located on or within the hollow main body, at the proximal extremity of the central longitudinal bore;
• an injection monitoring system comprising at least one or a plurality of magnetic sensors, the injection monitoring system being located at the proximal extremity of the bore of the hollow main body;
• the hollow main body further comprising an inner sleeve rotationally located within the central longitudinal bore, and configured to frictionally engage with an outer surface of the dose setting wheel to co-rotate around the central longitudinal axis with respect to said hollow main body, without axial translation along said central longitudinal axis, with the dose setting wheel during dose setting;
• wherein the inner sleeve is rotationally locked to the injection monitoring system such that rotation of said injection monitoring system causes rotation of said inner sleeve with respect to said hollow main body;
• and
• wherein the injection monitoring system is configured for translational movement with respect to said inner sleeve along the central longitudinal axis, during injection and/or ejection of a drug from the pen injection system.