A Study in China Evaluating the Safety and Efficacy of Adding Sitagliptin to Stable Therapy With Insulin With or Without Metformin in Participants With Type 2 Diabetes Mellitus (T2DM) (MK-0431-254)

Inclusion Criteria: * has T2DM * is currently on a stable regimen of pre-mixed, intermediate-acting, or long-acting insulin at a dose of at least 12 U/day, either alone or in combination with metformin \>=1500 mg/day for ≥ 10 weeks * has a Visit 1/Screening HbA1C between 7.5% and 11.0% * is a male, or a female who is highly unlikely to conceive during the study and for 14 days after the last dose of study medication Exclusion Criteria: * has been treated with any antihyperglycemic therapies other than a protocol-required insulin (alone or with metformin) within the prior 12 weeks or has ever been treated with a dipeptidyl peptidase-4 inhibitor or a glucagon-like peptide-1 mimetic or analogue * is currently on treatment with daily use (one or more injections per day) of pre-prandial short-acting or rapid-acting insulin * has a history of 2 or more episodes of hypoglycemia resulting in seizure, coma, or loss of consciousness, or has had recurrent episodes of hypoglycemia over the past 8 weeks * has a history of intolerance or hypersensitivity, or has any contraindication to sitagliptin, insulin, or metformin * is on a weight loss program and not in the maintenance phase, or has started a weight loss medication or has undergone bariatric surgery within 12 months * has undergone a surgical procedure within 4 weeks or has planned major surgery during the study * has a medical history of active liver disease * has had new or worsening signs or symptoms of coronary heart disease within the past 3 months, or has acute coronary syndrome, coronary artery intervention, or stroke or transient ischemic neurological disorder * has a diagnosis of congestive heart failure with New York Heart Association Class III - IV cardiac status * has a systolic blood pressure ≥ 160 mmHg or a diastolic blood pressure ≥ 90 mmHg * has human immunodeficiency virus (HIV) * has severe peripheral vascular disease * is currently being treated for hyperthyroidism or is on thyroid hormone therapy and has not been on a stable dose for at least 6 weeks * has a history of malignancy ≤ 5 years before the study, except for adequately treated basal cell or squamous cell skin cancer, or in situ cervical cancer * has a clinically important hematological disorder (such as aplastic anemia, myeloproliferative or myelodysplastic syndromes, thrombocytopenia) * is pregnant or breast feeding, or is expecting to conceive or donate eggs during the study, including 14 days after the last dose of study medication * is a user of recreational or illicit drugs or has had a recent history of drug abuse