Medicament delivery devices are routinely used by persons without formal medical training, i.e. patients where self-management of their condition is increasingly common. These circumstances set a number of requirements for medicament delivery devices of this kind The injector should be robust in construction, yet easy to use in terms of its operation by a user and the manipulation of the parts. In the case of those with diabetes, many users will be of impaired vision and may also be physically infirm. Devices that are too large or cumbersome may therefore prove difficult to use, particularly someone with reduced dexterity.
U.S. Pat. No. 5,989,221 describes an electronically controlled injection device in which the readying of the device for administering and the subsequent drug delivery therefrom is controlled by an electronic control unit. Specifically, the control unit comprises a position or attitude sensor for transmitting a signal so that the readying of the device cannot take place unless the longitudinal axis of the injection cartridge is in a predetermined direction. This is in the context of removing air or mixing drug components. The control unit is also operative for driving a piston rod a predetermined distance for delivery of a drug dose.
In such prior art devices, the user is still required to prime the device after installation of the medicament cartridge. Moreover, such devices may under dose particularly in cases where the medicament cartridge is not properly seated within the device after insertion by the user.