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 located within the central longitudinal bore, and the inner sleeve is configured to frictionally engage with an outer surface of the dose setting wheel to co-rotate around the central longitudinal axis, without axial translation along said central longitudinal axis, with the dose setting wheel during during dose setting;
• wherein the inner sleeve is connected to the injection monitoring system, and the connection between the inner sleeve and the injection monitoring system is adapted and configured to co-rotate both the inner sleeve and injection monitoring system about the central longitudinal axis during dose setting, and to translate the injection monitoring system along the central longitudinal axis, but not rotate said injection monitoring system around said central longitudinal axis, during injection and/or ejection of a drug from the pen injection system;
• wherein the hollow main body further comprises a distal body portion which extends around an outer surface of the body of the injection pen system at a location distal to the dose setting wheel, said distal body portion comprising diameter altering means configured to dynamically alter an inner diameter of the central longitudinal bore of the distal body portion from a first value to a second value different to the first value.