Thermal Stability of Insulin Made from Zinc Insulin Crystals

Abstract

A commercial insulin preparation was stored for 2 years, its normal shelf-life, at temperatures from 2" to 36". Full potency was retained for 2 years when the sample was kept at 2". However, the activity of the insulin decreased with time as the storage temperature was increased. After one year at room temperature (20" to 25") the activity of the insulin sample was 20 per cent below that stated on the label. Between 2" and 20" there was a consistent but not significant drop in activity. In the initial period the loss in potency may be essentially a reaction of zero order. THE stability of commercial insulin preparations is important, not only to the manufacturer, but also to the physician and in particular to the diabetic patient. Krogh and Hemmingsenl were the first to make a systematic study of the relation between temperature, time, and the destruction of amorphous insulin in a sterile aqueous solution. Their results suggested that the inactivation of insulin at a constant temperature followed a first order reaction, the rate of destruction at any moment being proportional to the concentration. In addition, it was reported that the optimal stability of an aqueous solution of insulin occurred between pH 2 and 4. Sahyun, Goodell and Nixon2, working with a low-ash insulin preparation, revealed that the addition of Zn++ to the aqueous medium improved the stability significantly. However, Lens3 could not confirm this stabilising effect of Zn++, and reported that the stability of crystalline insulin in aqueous solution was unpredictable. Lens concluded that the inactivation was not due to hydrolysis of the insulin, but could be attributed to denaturation or heat precipitation which was usually followed by an irreversible oxidative process.These inve~tigationsl-~ were carried out for short periods at elevated temperatures. There is a scarcity of information about the stability of commercial insulin preparations when kept at temperatures encountered under ordinary storage conditions for the expected shelf-life of the product. Consequently an experiment was designed to determine the rate at which insulin made from zinc insulin crystals loses activity when stored for a period of two years at temperatures of 2" to 36". MATERIALS AND METHODSInsulin Toronto, made from zinc insulin crystals, Lot 942-1, 40 International Units per ml., was used in this study, and was prepared from

Insulin aggregation in artificial delivery systems

“…The stability of insulin solutions at temperatures between -20 and +37 ~ is well documented [35]. One notable study [36] has defined stability as P(t) = po e-kt where t = time, Po = biological activity at t = 0, and k = e BT, where T = absolute temperature and B is a proportionality constant.…”

“…Whether denaturation of the hormone at elevated temperatures caused aggregation of the hormone is not clear from the literature. It has been observed that the decline with time in immunological activity is less than the decline in biological activity [35] which might perhaps be explained on the basis of aggregation or partial denaturation.…”

Stability of the 4th International Standard for Insulin

“…Earlier studies [1][2][3][4][5][6][7], have investigated the stability of insulin in solution or suspension. This report describes the stability of crystalline insulin.…”