Diabetes mellitus type 2 is associated with significant morbidity and mortality; and identifying new treatments for diabetes complications to be used alone or in combination with other therapies is a high priority. Hyperglycemia triggers proinflammatory pathways leading to damage in the kidneys, eyes and blood vessels; thus targeting proinflammatory lipid mediators called leukotrienes may represent a promising therapy for diabetes complications. This clinical trial seeks to investigate whether montelukast, a leukotriene antagonist, improves kidney, eye and vascular function in adult participants with type 2 diabetes and kidney disease.