Aims/IntroductionA prospective, 4‐week, single‐center, randomized, open‐label, parallel‐group, treat‐to‐target study was carried out to develop an algorithm for safe and effective switching from basal insulin to once‐daily insulin degludec/insulin aspart (IDegAsp) in patients with inadequately controlled type 2 diabetes.Materials and MethodsPatients were randomly assigned to continue their current basal insulin therapy (n = 10) or to switch to IDegAsp on a 1:1 unit basis (n = 10). The insulin dose could be titrated once weekly, targeting a self‐measured blood glucose of 80–100 mg/dL before breakfast. A mixed meal test was carried out at baseline and after 4 weeks.ResultsAfter 4 weeks, the mean daily dose of insulin was similarly increased by 60% in both groups, and there was a significant decrease of mean plasma glucose and glucose area under the glucose concentration vs time curve for 2 h in the meal test. The mean estimated treatment difference (IDegAsp group − basal insulin group) of the mean plasma glucose level was −28 mg/dL (95% confidence interval −47 to −8, P = 0.008) after 4 weeks and that of the area under the glucose concentration vs time curve for 2 h was −2,800 mg/min/dL (95% confidence interval −5,300 to −350, P = 0.028), confirming the superiority of IDegAsp to basal insulin. In the IDegAsp group, the 2‐h postprandial plasma glucose level was significantly decreased to the fasting plasma glucose range. There were no confirmed hypoglycemic episodes in either group during the 4‐week study period.ConclusionsAfter switching from basal insulin, the IDegAsp dose can be uptitrated by 60% based on fasting plasma glucose data. However, monitoring of postprandial glucose should be considered before further uptitration of IDegAsp.