Possible differences in potency of purified pork insulins: confirmation by the euglycemic clamp technique

A 33-year-old female with insulin-dependent diabetes mellitus (IDDM) for 14 yr had been taking a constant insulin dose for 2 yr. She experienced frequent hypoglycemic reactions when switched from purified pork insulin Iletin II NPH (LILLY) to Protophane (NOVO) which could not be explained by a change in either diet or body wt. A 75% reduction in dose led to a restoration of prior control. The euglycemic clamp technique was utilized to determine whether a difference in potency existed between the 2 commercially available purified pork insulins in this patient and 4 additional subjects, one of whom was not diabetic. There was an 18% difference in potency between insulins in the patient leading to these studies. A difference of more than 10% was noted in 3 of the 5 paired tests, suggesting increased potency (18, 29, 55.1%) of Actrapid (NOVO) compared with Iletin II Regular (LILLY). Until these preliminary observations are confirmed or denied, it is prudent to observe patients closely when switching from one brand of insulin to another even when the species of origin and purity are the same.