Inhaler

1. An inhaler comprising a housing, a blister strip contained within said housing, said blister strip having a surface and a plurality of blister pockets depending from said surface, each blister pocket containing a dose of medicament for inhalation by a user and, a blister strip drive mechanism including a drive wheel comprising a plurality of spokes, each spoke forming an arm of the blister drive mechanism, and a blister strip drive member shaped to contact the strip along a line defined by a crease between a blister pocket and said surface, to drive said strip, the blister strip drive member having leading and trailing blister strip contact edges on opposite sides of an axis extending in a radial direction through said arm and the blister strip drive member so that the leading blister strip contact edge contacts the strip along a line defined by the crease between one blister pocket and said surface when the drive member is rotated in one direction and so that the trailing blister strip contact edge contacts the strip along a line defined by the crease between an adjacent blister pocket and said surface, when the drive member is rotated in the opposite direction, wherein a blister separation, which is the distance between the creases of adjacent blister pockets, is substantially the same as the distance between the leading and trailing edges of the blister strip drive member and wherein the pitch of the blister strip is selected so that it is less than the pitch of the drive wheel, with the pitch of the blister strip being equal to the width of the blister plus the blister separation and the pitch of the blister strip drive member being equal to the length of a chord of the blister strip drive member plus the width of a tip of the blister strip drive member.

2. An inhaler according to claim 1 , wherein the blister strip drive member is configured to direct a larger component of force in a direction along the surface of the strip relative to a component of force directed against a blister pocket.

3. An inhaler according to claim 1 , wherein the blister strip drive member is disposed on an end of said arm.

4. An inhaler according to claim 1 , wherein the blister strip contact edge has a radius of up to 0.2 mm.

5. An inhaler according to claim 1 , wherein the blister strip drive member comprises an enlarged head on the end of the arm that tapers from the arm to the blister strip contact edge.

6. An inhaler according to claim 1 , wherein the blister strip drive member and arm are configured so that contact with the blister strip is restricted to the blister strip contact edge.

7. An inhaler according to claim 1 , wherein the arm, the blister strip drive member, or both are shaped such that the blister strip contact edge contacts the crease between a shaped blister pocket and the surface of the strip.

8. An inhaler according to claim 1 , wherein the arm, the blister strip drive member, or both are at least partially curved in shaped such that the blister strip contact edge contacts at least a partially curved line defined by the crease between a shaped blister pocket and the surface of the strip.

9. An inhaler according to claim 1 , wherein an end view of the blister strip drive member is substantially triangular or part triangular in shape, the apex of the triangle pointing in a radially inward direction along the length of the arm.

10. An inhaler according to claim 1 , wherein the blister strip drive member has a substantially flat or concave end face extending between said blister strip contact edges.

11. An inhaler according to claim 1 , wherein said end face extends in a plane lying substantially at right angles to a plane of the arm.

12. An inhaler according to claim 1 , wherein the drive mechanism is configured to sequentially move a blister into alignment with a blister opening member.

13. An inhaler according to claim 12 , wherein the inhaler comprises a mouthpiece and a cap to cover the mouthpiece, the drive mechanism being operable in response to movement of the cap by a user.

14. An inhaler according to claim 1 , wherein each blister pocket has a part cylindrical central region and part hemispherical end regions.