A Phase 2, Randomized, Parallel, Open-Label Comparator-Controlled Trial to Evaluate the Safety and Efficacy of LY3209590 in Study Participants With Type 1 Diabetes Mellitus Previously Treated With Multiple Daily Injection Therapy

Experimental: LY3209590 Algorithm 1 (Paper)

Algorithm 1 is a paper-based algorithm where dose adjustments were manually determined by the investigator based on fasting glucose and hypoglycemia data. LY3209590 was provided in a 20 milligram (mg) vial of reconstitutable lyophilized powder. Participants received individualized LY3209590 loading dose based on the basal insulin dose prior randomization and baseline fasting glucose by subcutaneous (SC) injection on day 1 followed by weekly adjustments for the first 12 weeks, then every 4 weeks, of a 26-week treatment period, to achieve target fasting glucose of \<=100 milligrams per deciliter (mg/dL).

Experimental: LY3209590 Algorithm 2 (Digital)

Algorithm 2 is a computer-based algorithm to determine dose adjustments. LY3209590 was provided in a 20 mg vial of reconstitutable lyophilized powder. Participants received individualized LY3209590 loading dose based on the basal insulin dose prior randomization and baseline fasting glucose by SC injection on day 1 followed by weekly adjustments for the first 12 weeks, then every 4 weeks, of a 26-week treatment period, to achieve target fasting glucose of \<=100 mg/dL.~As per protocol amendment (d) approved on 28-Oct-2020, this arm was terminated during the early enrollment phase due to technical issues with data entry.

Active_comparator: Insulin Degludec

Insulin degludec was provided as 100 units/milliliter (U/mL) in a prefilled pen. Participants received individually adjusted doses once daily by SC injection with a starting dose same as basal insulin dose prior randomization, during the 26-week treatment period, to achieve target fasting blood glucose of \<=100 mg/dL.