A combined rapid acting-
long acting insulin formulation has been developed wherein the pH of the 
rapid acting insulin is adjusted so that the 
long acting glargine remains soluble when they are mixed together. In the preferred embodiment, this injectable 
basal bolus insulin is administered 
before breakfast, provides adequate bolus 
insulin levels to cover the 
meal, does not produce 
hypoglycemia after the 
meal and provides adequate 
basal insulin for 24 hours. Lunch and dinner can be covered by two bolus injections of a fast acting, or a rapid acting or a very 
rapid acting insulin. As a result, a patient using intensive insulin therapy should only inject three, rather than four, times a day. Experiments have been performed to demonstrate, the importance of the addition of specific acids to hexameric insulin to enhance speed and amount of absorption and preserve bioactivity following dissociation into the monomeric form by addition of a chelator such as EDTA. As shown by the examples, the preferred acids are aspartic, maleic, succinic, glutamic and 
citric acid. These are added in addition to a chelator, preferably 
ethylenediaminetetraacetic acid (EDTA). The results show that the 
citric acid formulation was more effective at dropping the blood glucose rapidly than the identical rapid acting formulation prepared with HCl in swine. Charge masking by the polyacid appears to be responsible for rapid insulin absorption. EDTA was not effective when used with 
adipic acid, 
oxalic acid or HCl at hastening the absorption of insulin. These results confirm the results seen in clinical subjects and patients with diabetes treated with the 
rapid acting insulin in combination with 
citric acid and EDTA.