Similar to lente insulin, ultralente is a suspension of large, zinc-containing crystals that have been precipitated in an acetate buffer. Ultralente insulin reaches a peak gradually (14–18 h after injection), with a duration of action of up to 24 h. Long-acting insulins are used to provide a basal level of insulin.

Metzger, in Comprehensive Medicinal Chemistry II, 2007 6.19.6.5.3.4 Long-acting insulins (ultralente and insulin glargine) With these alterations, insulin detemir forms hexamers with slower dissociation and a longer duration of action. In insulin detemir, tyrosine at position B30 is lost with acylation at B29 that results in a fatty acid side chain (tetradecanoic acid) becoming linked with lysine. This insulin is slowly released into the circulation because of its acidic pH, which causes it to precipitate when injected subcutaneously. In insulin glargine, asparagine is replaced by glycine at position 21 of the α chain of the insulin molecule and the carboxyl terminal of the β chain is changed with the addition of arginine. These insulins provide a steady basal insulin profile with minimal peak action and are injected subcutaneously once daily. The onset of action is within two hours and they have a longer duration of action of up to 24 h. Longer-acting insulin analogues (insulin glargine and insulin detemir) are produced by genetic engineering. Wilding, in Clinical Biochemistry: Metabolic and Clinical Aspects (Third Edition), 2014 Long-acting insulin analogues

Insulin types and durations