Insulin glargine is produced by recombinant DNA technology using a non-pathogenic laboratory strain of Escherichia coli (K12) as the production organism. It is an analogue of human insulin made by replacing the asparagine residue at position A21 of the A-chain with glycine and adding two arginines to the C-terminus (positions B31 and 32) of the B-chain. The resulting protein is soluble at pH 4 and forms microprecipitates at physiological pH 7.4. Small amounts of insulin glargine are slowly released from microprecipitates giving the drug a long duration of action (up to 24 hours) and no pronounced peak concentration.