A method for preparing an insulin preparation for clinical use, which consists of crystallizing insulin under aseptic conditions of an aqueous solution containing insulin, with a ph comprised between 5 and 6, said solution containing at least one metal selected from the group formed by zinc, cobalt, nickel, cadmium, copper, manganese and iron, in sufficient quantity to effect the crystallization and to add after said crystallization a sterile aqueous solution containing at least one of said metals in an amount such that the mixture contains at least one of said metals in a non-toxic ratio equal to at least 20 x a x 10-3 milliequivalents per liter, where a is the number of international insulin units per milliliter, and increase the ph of the mixture to a value that can reach to be 8, which forms crystals with a metal content of at least about 0.35 milliequivalents per gram of crystals, said mixture being essentially free of ph-regulating anions having a higher affinity for the metal ions than insulin and thereby combining the metal with the adjusted ph, said crystals practically being insoluble in water at ph 7 and having a prolonged reducing action of blood sugar when suspended in water and injected parenterally. (Machine-translation by Google Translate, not legally binding)
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