• Adverse Events frequency and degree [ Time Frame: 26 weeks (4+22 weeks) ]
  Hypoglycemic episodes (glucose level < 3.9 mmol/l) frequency; Occurrence of local reactions at injection sites; Occurrence allergic reactions.
• Glycated hemoglobin [ Time Frame: 26 weeks ]
  Change in HbA1c from baseline
• Fasting Plasma Glucose Level [ Time Frame: 26 weeks ]
  Change in fasting plasma glucose level from baseline
• Seven-Point Glucose Testing [ Time Frame: 26 weeks ]
  Change in seven-point glucose testing results from baseline
• Basal Insulin Dose [ Time Frame: 26 weeks ]
  Change in basal insulin dose per body weight (U/kg) from baseline
• Total Insulin Dose [ Time Frame: 26 weeks ]
  Change in total insulin dose per body weight (U/kg) from baseline
• Body Mass Index [ Time Frame: 26 weeks ]
  Change in BMI from baseline
• Treatment Satisfaction [ Time Frame: 26 weeks ]
  Change in overall treatment satisfaction (DTSQ score) from baseline
• Achievement of Glycated Hemoglobin Goals [ Time Frame: 26 weeks ]
  The frequency of achievement glycated hemoglobin goals
• Achievement of Glycated Hemoglobin < 7% [ Time Frame: 26 weeks ]
  The frequency of achievement glycated hemoglobin < 7% ( 7% inclusive)

• Diabetes Mellitus, Type 1
• Diabetes Mellitus

• Drug: Lantus Solostar, 100 Units/mL Subcutaneous Solution
  4 weeks of glucose-level based dose titration, 22 weeks of treatment with stable doses
• Drug: Insulin RinGlar, 100 Units/mL Subcutaneous Solution
  4 weeks of glucose-level based dose titration, 22 weeks of treatment with stable doses

• Active Comparator: Lantus® SoloStar®
  Lantus® SoloStar® once a day, individually glucose-level based administered in stable doses, started before enrollement
  Intervention: Drug: Lantus Solostar, 100 Units/mL Subcutaneous Solution
• Experimental: Insulin RinGlar®
  Insulin RinGlar® once a day, individually glucose-level based administered in stable doses, started before enrollement
  Intervention: Drug: Insulin RinGlar, 100 Units/mL Subcutaneous Solution

Inclusion Criteria:

• Signed written consent
• Diabetes mellitus type 1 for at least 12 months prior to screening
• History of basis-bolus (multiple dose injection (MDI)) therapy in stable doses at least 30 days
• Glycated hemoglobin (HbA1c) level of 6.5 to 12.0 % at screening (both values inclusive)
• Body mass index (BMI) of 18.0 to 35 kg/m2 at screening (both values inclusive)
• Subject is able and willing to comply with the requirements of the study protocol

Exclusion Criteria:

• Contraindication to the use of Insulin glargine
• Insulin resistance over 1.5 U/kg insulin pro day
• History of treatment any biosimilar insulin
• History of treatment any experimental drugs or medical devices for 3 months prior to screening
• History of treatment insulin pump for 90 days prior to signed written consent or indication for use insulin pump
• Presence of severe diabetes complications
• History of severe hypoglycemia during 6 months prior to signed written consent
• History of 15 or more episodes mild hypoglycemia during 1 month prior to signed written consent
• History or presence of uncontrolled diabetes mellitus for 6 months prior to screening
• History of administration of glucocorticoids for 1 year prior to screening
• Administration of any immunosupressive drugs (Cyclosporinum, Methotrexatum, etc.)
• History of autoimmune disease, except vitiligo and controlled autoimmune polyglandular syndrome (APS) types 1-3, except adrenal insufficiency
• History of hypersensitivity to any of the active or inactive ingredients of the insulin/insulin analogue preparations used in the trial, OR history of significant allergic drug reactions
• History of severe allergic reactions
• Pregnant and breast-feeding women
• Acute inflammation disease for 3 weeks prior to screening
• Deviation of the laboratory results conducted during the screening:

Hemoglobin value < 9,0 g/dl; Hematocrit value < 30 %; ALT and AST value > 2 folds as high as maximal normal value; Serum bilirubin value > 1.5 folds as high as maximal normal value

• History of hematological disorders that can affect the reliability of HbA1c estimation (hemoglobinopathies, hemolytic anemia, etc.)
• Serious blood loss for 3 months prior to screening (blood donation, surgery procedure, etc.)
• Incomplete recovery after surgery procedure
• History of unstable angina, myocardial infarction, severe arrhythmia, heart failure III or IV NYHA for 1 year prior to screening
• History of stroke or TIA for 6 months prior to screening
• History of drug, alcohol abuse for 3 years prior to screening
• Inability follow to protocol
• History of oncological disease during 5 years prior to screening
• Serological evidence of human immunodeficiency virus (HIV), hepatitis B (HbSAg), hepatitis C (HCVAb) or syphilis (Treponema pallidum) antibodies at screening.
• History of transplantation, except 3 months after corneal transplant
• History or presence of a medical condition or disease that in the investigator's opinion would embarrass glycemic control and completion of the study