Efficacy, Safety and Preference Study of a Insulin Pen PDS290 vs. a Novo Nordisk Marketed Insulin Pen in Diabetics

Inclusion Criteria: * Informed consent obtained before any trial-related activities * Subjects diagnosed with type 1 or type 2 diabetes. If type 2 diabetics, treatment with or without oral anti diabetic medication is allowed * Current users of vial/syringe (pen naïve) treated with short-acting insulin (insulin aspart, glulisine or lispro) and once daily long-acting insulin (detemir or glargine) or once daily long-acting insulin (detemir or glargine) alone * Treatment with insulin (i.e. aspart, glulisine, lispro, detemir or glargine) for at least 6 months * Body Mass Index (BMI) less than 45.0 kg/m\^2 * HbA1c less than or equal to 9.0% at screening visit based on analysis from central laboratory * Able and willing to adhere to the trial-specific insulin regimen for the entire trial period Exclusion Criteria: * Females of childbearing potential who are pregnant, breast-feeding or intend to become pregnant or inadequate contraceptive techniques during the trial period (adequate contraceptive measures are considered as intrauterine device, oral contraceptives and barrier methods) * Previous participation in this trial (screening visit) * Systemic drugs that may influence glycaemic control (e.g., corticosteroids) * Known or suspected allergy to trial product(s) or related products * Known or suspected abuse of alcohol or drug abuse * Mental incapacity, unwillingness or language barriers precluding adequate understanding or cooperation * Previous treatment with sitagliptin * Clinically significant, active (or over the past 12 months) disease of the gastrointestinal, neurological, genitourinary, or haematological systems * Cardiac disease defined as: Decompensated heart failure (New York Heart class III or IV, unstable angina pectoris within the past 6 months of study enrolment, myocardial infarction within the past 12 months and a clinically significant history of arrhythmias or conduction delays on electrocardiogram (ECG) over the past 12 months * Any other severe acute or chronic illness as judged by the Investigator * Recurrent major hypoglycaemia (defined as severe central nervous system dysfunction associated with hypoglycaemia, requiring the assistance of another person) or hypoglycaemia unawareness (defined as a condition in which subjects no longer experience the usual warning signs of hypoglycaemia; the symptoms of hypoglycaemia may be different, less pronounced or even absent) or hospitalisation for diabetic ketoacidosis during the previous six months * Any other conditions that the Investigator judges would interfere with trial participation or evaluation of results (i.e. planned any diagnostic or therapeutic medical intervention such as surgery) * Participated in another clinical trial and received an investigational drug within the last 4 weeks