1.  Field of the Present Patent Application
The present patent application is generally directed to dose setting mechanisms for drug delivery devices.  More particularly, the present patent application is generally directed to drug delivery devices, such as pen type drug delivery devices.  Such devices provide for self administration of medicinal product from a multi-dose cartridge and permit a user to set the delivery dose.  The present application may find application in both disposable and reusable type drug delivery devices.  However, aspects of the invention may be equally applicable in other scenarios as well. 
2.  Background
Pen type drug delivery devices have application where regular injection by persons without formal medical training occurs.  This is increasingly common among patients having diabetes where self-treatment enables such patients to conduct effective management of their disease. 
Diabetes has been shown to cause certain problems.  For example, people with diabetes can get high blood pressure, kidney disease, nerve damage, heart disease, and even in certain circumstances blindness.  The damage caused by these problems may occur in patients whose blood sugar has been out of control for years.  Keeping blood sugar under control, by way of effective insulin administration, is one method that can help prevent this damage from occurring. 
In addition, people with diabetes can go into “diabetic coma” if their blood sugar is too high.  They can also develop blood sugar that is too low (i.e, hypoglycemia) if they don't get enough food, or they exercise too much without adjusting insulin or food.  Both diabetic coma and hypoglycemia can be very serious, and even fatal, if not treated quickly.  Closely watching blood sugar, being aware of the early signs and symptoms of blood sugar that is too high or too low, and treating those conditions early can prevent these problems from becoming too serious. 
Pen type drug delivery devices have been designed and developed to help patients suffering from diabetes so as to prevent such problems from occurring.  The circumstances identified above highlight a number of design considerations and criteria for drug delivery devices, especially those that may be used to treat diabetes.  As just one example, one requirement is that the drug delivery device must be robust in construction.  The drug delivery device must also be easy to use both in terms of the drug delivery device manipulation and understanding of the device's operation.  Diabetics have to inject themselves repeatedly with insulin solution and the volume of insulin to be injected may vary from patient to patient and even from injection to injection.  For at least this reason, certain diabetics may require drug delivery devices that allow the patient to inject successive measured dosages of the same or perhaps different preset volumes of insulin solution accurately and with minimum dexterity challenges.  This presents a further design challenge since, in the case of certain diabetics, users may have impaired vision and/or may be physically infirm with limited dexterity. 
The problem of a patient's impaired vision and limited dexterity is further exacerbated by drug delivery devices that force a patient to use his or her less dominant hand.  In other words, people suffering from diabetes who prefer to use their left hand (i.e., left handed patients) have an even greater desire or need for a drug delivery device that takes this user preference into consideration so that the patient is no longer forced to use his or her less dominant or weaker hand. 
For example, certain studies suggest that approximately ten percent of the adult population is left-handed.  It is also generally known that these left-handed individuals are sometimes placed at a disadvantage by the prevalence of right-handed tools and devices, such as medical drug delivery devices.  Many tools and drug delivery devices are designed to be comfortably used with a user's right hand but not the user's left hand.  As just one example, right-handed scissors, are arranged so that the line being cut along can be seen by a right-handed user, but is obscured to a left-handed user.  Furthermore, the handles of these scissors are often molded in a way that is difficult or uncomfortable to be held by a left-handed user.  Consequently, extensive use in such cases can lead to varying levels of efficiency and/or discomfort.  As just another example of the right handed nature of tools and devices, the computer mouse is sometimes made to fit the right hand better than the left hand. 
Consequently, with respect to the use of drug devices, many left handed patients, especially those already suffering from certain limitations such as partial blindness and limited dexterity, are further facing a heightened challenge when using a right-handed drug delivery device.  These patients are being forced to use their less dominant hand to manipulate certain drug delivery devices, many of which have complicated dose setting and injection operations.  This may be especially true where the left handed patient must user his or her less dominant right hand to manipulate the device to set an accurate dose of medicine (such as insulin) and then also inject a dose of medicine.  As already mentioned above, inaccurate dose setting or injection of certain self administered drugs, such as insulin, could lead to fatal results. 
There is, therefore, a general need to take these left handed and right handed issues into consideration in the design and development of drug delivery devices.  Such drug delivery devices would allow a user to use his or her more dominant hand (their left hand) to set and then inject an accurate dose of medication.