An insulin analog is an altered form of insulin, different from any occurring in nature, but still available to the human body for performing the same action as human insulin in terms of glycemic control. Through genetic engineering of the underlying DNA, the amino acid sequence of insulin can be changed to alter its ADME (absorption, distribution, metabolism, and excretion) characteristics.

These modifications have been used to create two types of insulin analogs: those that are more readily absorbed from the injection site and therefore act faster than natural insulin injected subcutaneously, intended to supply the bolus level of insulin needed after a meal; and those that are released slowly over a period of between 8 and 24 hours, intended to supply the basal level of insulin for the day.

Animal insulin

The amino acid sequence for insulin is almost the same in different mammals. Porcine insulin has only a single amino acid variation from the human variety, and bovine insulin varies by three amino acids. Both are active on the human receptor with approximately the same strength. Prior to the introduction of biosynthetic human insulin, insulin derived from sharks was widely used in Japan. Even insulin from some species of fish may be effective in humans. Non-human insulins can cause allergic reactions in a tiny number of people, as can genetically engineered "human" insulin. Synthetic "human" insulin has largely replaced animal insulin. With the advent of high-pressure liquid chromatography (HPLC) equipment, the level of purification of animal-sourced insulins has reached as high as 99%, whereas the purity level of synthetic human insulins made via recombinant DNA has only attained a maximum purity level of 97%, which raises questions about the claim of synthetic insulin's purity relative to animal-sourced insulin varieties.

Chemically and enzymatically modified insulins

Before biosynthetic human recombinant analogues were available, porcine insulin was chemically converted into human insulin. Chemical modifications of the amino acid side chains at the N-terminus and/or the C-terminus were made in order to alter the ADME characteristics of the analogue. Novo Nordisk was able to enzymatically convert porcine insulin into 'human' insulin by removing the single amino acid that varies from the human variety, and chemically adding the correct one.

Non hexameric insulin analogs

Unmodified human and porcine insulins tend to complex with zinc in the blood, forming hexamers. Insulin in the form of a hexamer will not bind to its receptors, so the hexamer has to slowly equilibrate back into its monomers to be biologically useful. Hexameric insulin is not readily available for the body when insulin is needed in larger doses delivered subcutaneously (although this is more a function of subcutaneously administering insulin, as interveinously dosed insulin is distributed rapidly to the cell receptors and therefore does not generally encounter this problem), such as after a meal. Zinc combinations of insulin are used for slow release of basal insulin. Basal insulin is the amount the body needs through the day excluding the amount needed after meals. Non hexameric insulins were developed to be faster acting and to replace the injection of normal unmodified insulin before a meal.