A Study of the Safety and Efficacy of MK-1293 Compared to Lantus™ in Participants With Type 1 Diabetes Mellitus (T1DM) (MK-1293-003)

Inclusion Criteria:

- T1DM For at least 1 year

- is currently using or has been using prandial insulin for at least 4 weeks.
Participants taking any type of basal insulin should require a total daily dose of
>=10 units/day. For participants currently taking pre-mixed insulin, the basal
insulin component should be equivalent to a total daily dose of >=10 units/day.

- is male, or is female who is not of reproductive potential or if of reproductive
potential agrees to remain abstinent or use (or have their partner use) an acceptable
method of birth control during the study and for 14 days after the last dose of study
medication

Exclusion Criteria:

- has had 1 or more severe hypoglycemic episodes associated with hypoglycemic seizure
or loss of consciousness within the past 6 months

- history of ketoacidosis in the last 6 months

- participant, as assessed by the investigator, is not appropriate for or does not
agree to target a fasting glucose of 70-100 mg/dL [3.9 -5.6 mmol/L].

- history of intolerance or hypersensitivity to Lantus™ or contraindication to Lantus™
or one of its excipients

- used a formulation of insulin glargine other than Lantus™

- has received injectable incretin-based therapy within the past 8 weeks

- on a weight loss program and not in the maintenance phase, or has started a weight
loss medication within the past 8 weeks

- has undergone bariatric surgery within the past 12 months

- is likely to require treatment for 2 or more consecutive weeks or repeated courses of
corticosteroids (note: inhaled, nasal, and topical corticosteroids are permitted)

- has undergone a surgical procedure within the past 4 weeks or has planned major
surgery during the study

- has new or worsening signs or symptoms of coronary heart disease or congestive heart
failure within the past 3 months, or has any following disorders within the past 3
months: acute coronary syndrome, coronary artery intervention, stroke or transient
ischemic neurological disorder

- has severe peripheral vascular disease

- has high blood pressure

- has chronic myopathy, or a progressive neurological or neuromuscular disorder

- has active neuropathy

- history of active liver disease (other than non-alcoholic hepatic steatosis),
including chronic active hepatitis B or C, primary biliary cirrhosis, or symptomatic
gallbladder disease

- has human immunodeficiency virus (HIV)

- has a hematological disorder (such as aplastic anemia, myeloproliferative or
myelodysplastic syndromes, thrombocytopenia)

- history of malignancy in the past 5 years, except for adequately treated basal cell
or squamous cell skin cancer, or in situ cervical cancer

- history of melanoma, leukemia, lymphoma, or renal cell carcinoma

- is currently being treated for hyperthyroidism or has been on a stable dose of
thyroid hormone replacement therapy for <6 weeks

- is a user of recreational or illicit drugs or has had a recent history of drug or
alcohol abuse or dependence

- is pregnant or breast-feeding, or is expecting to conceive or donate eggs

- has donated blood products or has had phlebotomy of >300 mL within the past 8 weeks
or intends to donate blood products during the study

- has poor mental function or works the night shift