Patent ID: RE43834

Claim:
A medication delivery pen comprising: a housing having proximal and distal ends and including a holder for containing a cartridge containing a medication to be delivered through a conduit connected to the cartridge , ; a piston rod having a not circular cross-section and an outer thread , and ; a piston rod drive for driving said piston rod in a distal direction inside the cartridge, said piston rod drive including a first part rotatably mounted within said housing and mating with the not circular cross-section of said piston rod, and a second part integral with said housing and having an internal thread mating the thread of said piston rod to form a self-locking thread connection, wherein rotation of said first part in a first direction relative to said second part drives said piston rod in a distal direction; and a one-way coupling comprising: a) an annular ring of equally spaced internal ratchet notches situated on the inside of said housing, which internal notches have a steep front edge and a ramp shaped trailing edge, b) a pawl surrounding said piston rod and having at least a pair of resilient arms, each arm having a free end, said pawl being connected with said first part of said piston rod drive, and c) means situated on said free end of each arm for engaging in the internal ratchet notches of said annular ring, which means abuts said steep front edge of said internal notches, thereby preventing said pawl body from rotating in one direction relatively to said housing, the prevented direction being one by which the piston rod would be transported in a proximal direction ; wherein in situation of use, the piston rod does not rotate and advance axially when a dose setting member is rotated in either a clockwise or anticlockwise direction unless an axial force is applied to the pen, wherein when the axial force is applied to press an injection button home, the axial force is transformed to result in rotation of the piston rod in a direction which in turn causes the piston rod to advance distally .