Preparation of a microcrystalline suspension formulation of Lys(B28)Pro(B29)-human insulin with ultralente properties

The monomeric analogue, Lys(B28)Pro(B29)-human insulin (LysPro), has been c rystallized using similar conditions employed to prepare extended-acting in sulin ultralente formulations. In the presence of zinc ions, sodium acetate and sodium chloride, but without phenolic preservative, LysPro surprisingl y forms smalt rhombohedral crystals with similar morphology to human insuli n ultralente crystals with a mean particle size of 20 +/- 1 pm. X-ray powde r diffraction studies on the LysPro crystals prior to dilution in ultralent e vehicle ([NaCl] 1.2 M) revealed the presence of T3R3f hexamers. Consisten t with human insulin ultralente preparations, LysPro crystals formulated as an ultralente suspension ([NaCl] = 0.12 M) contain T-6 hexamers indicating that a conformational change occurs in the hexamer units of the crystals u pon dilution of the salt concentration. The pharmacological properties of s ubcutaneously administered ultralente LysPro (ULP) were compared to ultrale nte human Insulin (UHI) using a conscious dog model (n = 5) with glucose le vels clamped at basal. There were no statistically significant differences between the kinetic and dynamic responses of ULP compared to UHI [C-max (ng /mL): 3.58 +/- 0.76, ULP and 3.61 +/- 0.66, UHI; T-max (min): 226 +/- 30, U LP and 185 +/- 42, UHI; R-max (mg/kg min): 11.2 +/- 1.9, ULP and 13.3 +/- 2 .0, UHI; and T-Rmax (min): 336 +/- 11, ULP and 285 +/- 57, UHI]. Although t he Pro to Lys sequence inversion destabilizes insulin self-assembly and gre atly alters the time action of soluble LysPro preparations, this modificati on has now been found neither to prevent the formation of ultratente crysta ls in the absence of phenolics nor to compromise the protracted activity of the insulin analogue suspension.