A Research Study of How Different Amounts of a New Medicine NNC0148-0287 C (Insulin 287) Works on the Blood Sugar of People Who Are Japanese With Type 1 Diabetes When Given Once a Week

A Multiple-dose Trial Investigating the Safety, Tolerability, Pharmacokinetics and Pharmacodynamics of NNC0148-0287 C (Insulin 287) for Subcutaneous Administration in Japanese Subjects With Type 1 Diabetes

This study will look at how insulin 287 works, if it is safe and the side effects in people who are Japanese with type 1 diabetes. The study will test how insulin goes through your blood, how long it stays there and how the blood sugar is lowered. Insulin 287 is a new medicine. Insulin glargine is already approved to treat diabetes. The study doctors can prescribe insulin glargine. The participants will get both of the insulins in a random order. The participants will get 8 weekly doses of insulin 287 and 14 daily doses of insulin glargine. There will also be a run-in period of 2 days to 7 weeks when the participants inject insulin glargine every day before they start insulin 287 period or insulin glargine period. All doses will be injected under the skin. During the run-in period, the participants adjust the insulin glargine dose and make their blood sugar levels stable. From the run-in period, the participants will take insulin aspart as bolus insulin. The study will last for about 16 - 28 weeks. The participants will have 24 visits with the study doctor. There will be 3 glucose clamps where the participants' blood sugar is tested over time. The participants cannot be in the study if the study doctor thinks that there are risks for their health.

Inclusion Criteria:

• Male or female, Japanese subjects, aged 20 - 64 years (both inclusive) at the time of signing informed consent.
• Diagnosed with type 1 diabetes mellitus greater than or equal to 1 year prior to the day of screening.
• Current daily basal insulin treatment greater than or equal to 0.2 U/kg/day.
• Body mass index between 18.5 and 28.0 kg/m^2 (both inclusive).
• HbA1c less than or equal to 9.0%.

Exclusion Criteria:

• History or presence of any clinically relevant respiratory, metabolic, renal, hepatic, gastrointestinal or endocrinological conditions (except conditions associated with diabetes mellitus).
• Female who is pregnant, breast-feeding or intends to become pregnant or is of child-bearing potential and not using adequate contraceptive methods.
• Known or suspected hypersensitivity to trial products or related products