Stability of insulin mixtures in disposable plastic insulin syringes

The miscibility of short and long acting porcine, human and bovine insulins has been investigated using HPLC. Soluble insulin is rapidly lost from solution when mixed with both isophane and zinc insulin, although the mechanism may be different in these two cases. The time for up to 50% or more to be lost is often less than 2 min. The percentage lost is dependent upon the ratio of the mixture and the type and origin of the insulin. In the case of soluble: zinc mixtures it is greatest for porcine and least for bovine, in the case of soluble: isophane mixtures it was least for human and greatest for bovine. The greater the original amount of soluble insulin present the less the loss. The results help explain recent clinical reports that mixtures of soluble and zinc insulins fail to achieve satisfactory control of post-prandial blood sugar levels.