GB766995A - Improvements in or relating to the production of insulin crystals - Google Patents

Abstract

In the crystallization of insulin from aqueous solution the size of the resulting crystals is controlled by adding a predetermined quantity of insulin seed crystals of a predetermined size. Spontaneous crystallization may be suppressed as far as possible or slight spontaneous crystallization may be allowed.ALSO:A process of crystallizing insulin from an aqueous medium of pH 5 to 7 in the presence of a crystallization-promoting metal e.g. zinc, cobalt, nickel, cadmium, copper, iron, or manganese, comprises seeding the medium with insulin crystals in an amount given by the equation <FORM:0766995/VI/1> where P is the weight in grams of seed crystals used, I is the weight in grams of insulin to be crystallized, and dp and di are the greatest size and the desired upper limit for size in micron of the seed crystals and crystallized insulin respectively. The size of the crystal is defined as the length in micron of the longest diagonal of the crystal. Crystals of uniform size are obtained by preventing spontaneous crystallization e.g. by addition of a buffer substance the anion of which does not bind the crystallization-promoting metal at neutral reaction, and by the use of seed crystals of mainly the same size. Suitable buffers are borate, diethylbarbiturate, maleate or acetate buffers. Crystallization may take place in the presence of halogen in ionic form e.g. as the halide of ammonia, alkali or alkaline earth metals, or mixtures thereof, in a concentration above 0.2 mole per litre, as in Specification 733,740 in which case phosphate or citrate buffers may be used. A basic or acidic solution of insulin which may or may not contain the required content of metals, may be adjusted to the crystallization pH by means of a buffer; the insulin may be precipitated amorphously and subsequently changed into crystalline form by the addition of seed crystals together with the necessary metals, e.g. as an aqueous solution of the metal salt or by the addition of the seed crystals which may themselves exhibit sufficient metal content. The seed crystals may be formed by the process of Specification 766,994 and may be added in the form of an aqueous suspension or in dry freeze dried form. An injectable insulin preparation may be prepared in conjunction with the process of Specification 709,927.