Preparation and characterization of a cocrystalline suspension of [LysB28,ProB29] human insulin analogue

Soluble preparations of [Lys(B28),Pro(B29)]-human insulin analogue (LysPro) exhibit more rapid absorption than human insulin upon subcutaneous injection. Biphasic mixtures of LysPro and intermediate-acting insulin suspensions could provide advantages over current preparations for the treatment of diabetes. To prepare biphasic mixtures of LysPro, a suspension formulation of the analogue is required. We have devised a method for crystallizing LysPro with the basic peptide protamine yielding neutral protamine LysPro (NPL) suspension. The crystallization conditions are strongly dependent on the precipitation procedure and temperature. Using various techniques, the crystalline and suspension characteristics of NPL are found to be similar to human insulin (neutral protamine Hagedorn, NPH) (8:1 molar ratio insulin:protamine, rod-shaped crystals, particle size of 4.0-6.0 mu m, and Point of Zero Charge at 6.0-7.0). Using a dog model with NPL or NPH injected subcutaneously and glucose levels clamped at basal, NPL was found to have kinetic and dynamic responses analogous to human insulin NPH [C-max (maximal insulin or LysPro concentration, ng/mL) of 2.61 +/- 0.22, NPL; 2.58 +/- 0.36, NPH, attained at T-max (min) of 93 +/- 22, NPL; 145 +/- 33 NPH, and R-max (maximal rate of glucose infusion, mg/kg min) of 10.8 +/- 1.2, NPL; 13.2 +/- 1.9, NPH, attained at TRmax (min) of 277 +/- 58, NPL; 265 +/- 38, NPH]. There are no statistically significant differences between the insulin curves or the glucose responses. These results provide insight into the mechanism of action of NPH suspensions and the relationship to duration of action. Furthermore, the formulation of a suspension of LysPro having an intermediate time-action makes possible the preparation of stable biphasic mixtures containing LysPro and NPL.