Stability of U-10 and U-50 dilutions of insulin lispro.

BACKGROUND: Insulin lispro, a rapid acting analog of human insulin, has been shown to be useful in the treatment of children with diabetes. However, lower concentrations of this insulin may be needed to facilitate optimal clinical use. Therefore, the stability of insulin lispro when diluted with an appropriate diluent was evaluated. METHODS: Insulin lispro (U-100, 100 U/mL) was diluted with sterile Neutral Protamine Hagedorn (NPH) diluent to U-10 and U-50. After storage for 7, 14, 21, 28, and 32 days at 5 degrees C and 30 degrees C, the diluted insulins were analyzed by high-performance liquid chromatography (HPLC) to determine potency, purity, polymer, and preservative (metacresol or phenol) content in addition to physical appearance and pH determinations. Microbiological testing for preservative effectiveness was performed on the U-10 and U-50 solutions after 32 days at both temperatures. RESULTS: U-10 and U-50 dilutions of insulin lispro stored at 5 degrees C and 30 degrees C maintained potency and purity throughout the 32-day testing period. Additionally, both control and diluted vials maintained antimicrobial effectiveness. CONCLUSION: Insulin lispro when diluted with the appropriate diluent demonstrates acceptable stability when stored at 5 degrees C and 30 degrees C for a period of 32 days.

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 crystallized using similar conditions employed to prepare extended-acting insulin ultralente formulations. In the presence of zinc ions, sodium acetate and sodium chloride, but without phenolic preservative, LysPro surprisingly forms small rhombohedral crystals with similar morphology to human insulin ultralente crystals with a mean particle size of 20 +/- 1 microm. X-ray powder diffraction studies on the LysPro crystals prior to dilution in ultralente vehicle ([NaCl] = 1.2 M) revealed the presence of T(3)R(3)(f) hexamers. Consistent 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 upon dilution of the salt concentration. The pharmacological properties of subcutaneously administered ultralente LysPro (ULP) were compared to ultralente human insulin (UHI) using a conscious dog model (n = 5) with glucose levels 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, ULP 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 the Pro to Lys sequence inversion destabilizes insulin self-assembly and greatly alters the time action of soluble LysPro preparations, this modification has now been found neither to prevent the formation of ultralente crystals in the absence of phenolics nor to compromise the protracted activity of the insulin analogue suspension.

Self-association properties of monomeric insulin analogs under formulation conditions.

PURPOSE: The purpose of the current study was to investigate the effects of two important excipients, zinc and m-cresol, on the self-association properties of a series of monomeric insulin analogs. In this way, the effects on formulation behavior of individual amino acid substitutions in the C-terminal region of the insulin B-chain could be compared. METHODS: The self-association of ten insulin analogs was monitored by equilibrium and velocity analytical ultracentrifugation under three different conditions: (i) in neutral buffer alone; (ii) in neutral buffer containing zinc ion; and (iii) in neutral buffer containing both zinc ion and phenolic preservative (a typical condition for insulin formulations). The self-association properties of these analogs were compared to those of human insulin and the rapid-acting insulin analog Lys(B28)Pro(B29)-human insulin. RESULTS: The analogs in the current study exhibited a wide range of association properties when examined in neutral buffer alone or in neutral buffer containing zinc ion. However, all of these analogs had association properties similar to human insulin in the presence of both zinc and m-cresol. Under these formulation conditions each analog had an apparent sedimentation coefficient of s* = 2.9-3.1 S, which corresponds to the insulin hexamer. CONCLUSIONS: Analogs with changes in the B27-B29 region of human insulin form soluble hexamers in the presence of both zinc and m-cresol, and m-cresol binding overrides the otherwise destabilizing effects of these mutations on self assembly.