Placebo-controlled, double blind (triple-dummy technique), randomised parallel design comparison of three oral doses (2.5 mg, 10 mg, and 25 mg) of empagliflozin in patients with T1DM as adjunctive therapy to insulin over 28 days. Patients will undergo a 14-day open-label placebo run-in period before randomisation. Background insulin therapy will be kept stable during the first 7 days of the treatment period and will be freely adjusted thereafter.

Inclusion criteria:

• Signed and dated written informed consent
• Male or female patient receiving insulin for treatment of T1DM for at least 12 months
• C-peptide < 1.5 ng/mL
• Age 18 to 65 years
• HbA1c of 7.5% to 10.5%
• Multiple daily injections (MDI) of any type of insulin
• Willing to follow an established and individualized carbohydrate counting method and an insulin administration algorithm
• Body Mass Index of 18.5 to 35.0 kg/m2
• Estimated glomerular filtration rate 60 to 150 mL/min/1.73 m²
• Able and willing to perform study assessments according to investigator's judgement
• Compliance with trial drug administration 80% to 120% during run-in period
• Willing not to take any paracetamol containing drugs during the trial

Exclusion criteria:

• Acute symptomatic urinary tract infection or genital infection, chronic or recurrent cystitis
• History of type 2 diabetes mellitus, maturity onset diabetes of the young (MODY), pancreatic surgery or chronic pancreatitis
• Pancreas, pancreatic islet cells or renal transplant recipient
• Type 1 diabetes mellitus treatment with any other antihyperglycaemic drug except insulin within last 3 months or history of clinically relevant hypersensitivity
• Occurrence of hypoglycaemia that required hospitalization or treatment by an emergency physician or paramedic within last 3 months
• Hypoglycaemia unawareness or frequent episodes of unexplained hypoglycaemia
• Occurrence of diabetic ketoacidosis that required hospitalization or treatment by an emergency physician or paramedic within last 12 months
• History of macrovascular disease including cardiovascular, cerebrovascular and peripheral artery disease
• Autonomic neuropathy with gastroparesis
• Brittle diabetes
• Liver disease
• Treatment with anti-obesity drugs, surgery or aggressive diet regimen leading to unstable body weight
• Treatment with systemic corticosteroids
• Change in dose of thyroid hormones within last 6 weeks or planned change or initiation of such a therapy
• Medical history of cancer or treatment for cancer in the last five years
• Blood dyscrasias or any disorders causing haemolysis or unstable red blood cells
• Alcohol or drug abuse that would interfere with trial participation or any ongoing clinical condition that would jeopardize patient's or site personnel's safety or study compliance
• Intake of an investigational drug in another trial within last 30 days
• Not able to understand and comply with study requirements
• Pre-menopausal women who are nursing or pregnant or of child-bearing potential and are not practising an acceptable method of birth control