Sitagliptin, through its effects on sensitizing alpha-cell sensitivity to glucose, can initiate counter-regulatory glucagon responses at higher glycemic thresholds, thus reducing the number of clinically apparent hypoglycemic episodes, and/or ameliorating the severity of hypoglycemic episodes in the case that they should occur. The endpoints have defined such that consequences of this hypothesis can be measured.

Inclusion Criteria:

• Male or female subject with diabetes mellitus type 2.
• Age between 18 and 64 years, both inclusive.
• HbA1c <= 8.5%.
• Stable treatment with insulin glargine (any dose) and metformin (>= 1500 mg/day or at highest tolerated dose) for at least 3 months prior to inclusion into the trial with or without additional oral glucose-lowering agents (except thiazolidinediones).
• Considered generally healthy (apart from diabetes mellitus type 2 and associated conditions such as hypertension, hyperlipidaemia and hyperuricaemia) upon completion of medical history, physical examination, vital signs, ECG and analysis of laboratory safety variables, as judged by the Investigator.

Exclusion Criteria:

• Known or suspected hypersensitivity to sitagliptin or related products.
• More than one episode of severe hypoglycaemia with seizure, coma or requiring medical assistance of another person during the past 6 months or hypoglycaemic unawareness as judged by the Investigator.
• Current or previous treatment (less than 3 months prior to screening) with insulin products other than insulin glargine and/or with Glucagon-like peptide (GLP) 1 receptor agonists and/or with thiazolidinediones.
• Unwillingness to wash-off any oral glucose-lowering agents other than metformin.

Participants of both arms are included here

For each participant from baseline to end of trial, with a range from 7-53 weeks per participant, on average 11 weeks

In this report, only treatment-emergent adverse events (TEAEs) are reported, occurring after randomisation. No AEs were reported for the washout period.

This is a double-blind randomised trial. Except for the unblinded persons involved in the preparation of the IMP (these persons are not involved in any other trial activities), everyone involved in the trial will be blinded until completion of the trial and the final data review.