Dose delivery mechanism

1. An injection device comprising:

a. a housing having a first longitudinal axis;

b. a medicament cartridge holder arranged around a second longitudinal axis which is substantially parallel to but offset from the first longitudinal axis; and

c. a drive assembly including a drive shaft arranged concentrically about said first longitudinal axis, a worm gear engaged in a rack wherein rotation of said worm gear about the first longitudinal axis causes the rack to advance axially forward or backward with respect to said worm gear, and a worm gear rotational lock engageable with the worm gear so as to substantially prevent rotation of the worm gear when engaged with the worm gear.

2. The injection device of claim 1 wherein the drive assembly further comprises a rotational to axial coupling, where the drive assembly is rotationally drivable by a torsion spring and is arranged to provide an axial force for ejecting a dose from the injection device.

3. The injection device of claim 1 wherein said worm gear is arranged around said first longitudinal axis and said rack is arranged around said second longitudinal axis.

4. The injection device of claim 1 wherein the worm gear rotational lock is disengageable from a forward end of the worm gear by being pushed axially forward by the drive shaft.

5. The injection device of claim 1 wherein the drive assembly further comprises means engageable between the drive shaft and the worm gear and which, when engaged, rotationally lock the drive shaft and worm gear together.

6. The injection device of claim 5 wherein the means is a clutch.

7. The injection device of claim 6 wherein the clutch comprises splines.

8. The injection device of claim 5 wherein said means is engageable before said worm gear rotational lock is disengaged.

9. The injection device of claim 1 further comprising a medicament cartridge.

10. The injection device of claim 9 further comprising a medicament contained in the medicament cartridge.

11. The injection device of claim 10 , wherein the medicament is selected from the group consisting of: antipsychotic substances including risperidone, hormones, antitoxins, substances for the control of pain, immunosuppressives, substances for the control of thrombosis, substances for the control or elimination of infection, peptides, proteins, human insulin or a human insulin analogue or derivative, polysaccharide, DNA, RNA, enzymes, antibodies, oligonucleotide, antiallergics, antihistamines, anti- inflammatories, corticosteroids, disease modifying anti-rheumatic drugs, erythropoietin, or vaccines, for use in the treatment or prevention of rheumatoid arthritis, psoriatic arthritis, ankylosing spondylitis, ulcerative colitis, hormone deficiency, toxicity, pain, thrombosis, infection, diabetes mellitus, diabetic retinopathy, acute coronary syndrome, angina, myocardial infarction, atherosclerosis, cancer, macular degeneration, allergy, hay fever, inflammation, anaemia, or myelodysplasia, and in the expression of protective immunity.

12. The injection device of claim 1 , wherein the worm gear rotational lock is engageable in a forward end of the worm gear.

13. An injection device comprising:

a. a housing having a first longitudinal axis;

b. a medicament cartridge holder arranged around a second longitudinal axis which is substantially parallel to but offset from the first longitudinal axis; and

c. a drive assembly including a drive shaft arranged concentrically about said first longitudinal axis, a worm gear engaged in a rack wherein rotation of said worm gear about the first longitudinal axis causes the rack to advance axially forward or backward with respect to said worm gear, and a worm gear rotational lock engageable in a forward end of the worm gear.

14. The injection device of claim 13 , wherein the drive assembly further comprises a rotational to axial coupling, where the drive assembly is rotationally drivable by a torsion spring and is arranged to provide an axial force for ejecting a dose from the injection device.

15. The injection device of claim 13 , wherein said worm gear is arranged around said first longitudinal axis and said rack is arranged around said second longitudinal axis.

16. The injection device of claim 13 , wherein the worm gear rotational lock is disengageable from a forward end of the worm gear by being pushed axially forward by the drive shaft.

17. The injection device of claim 13 , wherein the drive assembly further comprises a clutch engageable between the drive shaft and the worm gear and which, when engaged, rotationally lock the drive shaft and worm gear together.

18. The injection device of claim 17 , wherein the clutch comprises splines.

19. The injection device of claim 17 , wherein said clutch is engageable before said worm gear rotational lock is disengaged.

20. The injection device of claim 19 , wherein the medicament is selected from the group consisting of: antipsychotic substances including risperidone, hormones, antitoxins, substances for the control of pain, immunosuppressives, substances for the control of thrombosis, substances for the control or elimination of infection, peptides, proteins, human insulin or a human insulin analogue or derivative, polysaccharide, DNA, RNA, enzymes, antibodies, oligonucleotide, antiallergics, antihistamines, anti-inflammatories, corticosteroids, disease modifying anti-rheumatic drugs, erythropoietin, or vaccines, for use in the treatment or prevention of rheumatoid arthritis, psoriatic arthritis, ankylosing spondylitis, ulcerative colitis, hormone deficiency, toxicity, pain, thrombosis, infection, diabetes mellitus, diabetic retinopathy, acute coronary syndrome, angina, myocardial infarction, atherosclerosis, cancer, macular degeneration, allergy, hay fever, inflammation, anaemia, or myelodysplasia, and in the expression of protective immunity.

21. The injection device of claim 13 , further comprising a medicament cartridge including a medicament.