Formulations of sugars with amino acids or mannitol--influence of concentration ratio on the properties of the freeze-concentrate and the lyophilizate.

Formulations consisting of either sucrose or trehalose with glycine, lysine-HCl, or mannitol were studied to determine how the ratio of the excipients affects the design of the lyophilization program and the properties of the final cake. Glass transitions (Tg', Tg), crystallization temperatures, and eutectic melting temperatures were measured by differential scanning calorimetry, the physical state of the excipients was determined by x-ray powder diffraction, and residual moisture was measured by Karl Fischer titration. The addition of increasing amounts of glycine, lysine-HCl, or mannitol to a sucrose solution caused a progressive depression of the Tg', an effect that was more pronounced with the amino acids. In equivalent ratios with sucrose, the two amino acids induced a comparable Tg' shift due to their low Tg' values. For lysine-HCl, two apparent Tg' with midpoint temperatures of -69 and -56 degrees C were measured. For mannitol, the Tg' depression was unexpected because mannitol exhibits a higher Tg' than that of sucrose. During lyophilization, the ratio of the amorphous amino acids or mannitol to the sugar determined whether crystallization could be induced by an annealing step performed after freezing. Crystallization could be verified by a shift of the formerly depressed Tg' back to the value of the sugar and by the detection of the eutectic melting peak of the crystallized compound. The crystallized excipients served as excellent bulking agents. In the freeze-dried cake, amorphous glycine and even more amorphous mannitol lowered the Tg value. If the cake was stored above Tg, subsequent crystallization of mannitol occurred. The results emphasize that the qualitative and quantitative composition of a formulation has profound implications on the design of a lyophilization program and on the characteristics of the freeze-dried cake.