OBJECTIVE—To compare insulin levels and actions in patients with type 1 diabetes after subcutaneous injection of the rapid-acting insulin analogs aspart and lispro.

RESEARCH DESIGN AND METHODS—Seven C-peptide–negative patients with type 1 diabetes (two men and five women) were studied at the General Clinical Research Center at Temple University Hospital two times, 1 month apart. Their plasma glucose was normalized overnight by intravenous infusion of insulin. The next morning, they received subcutaneous injections of either aspart or lispro (9.4 ± 1.9 U) in random order. For the next 4–5 h, their plasma glucose was clamped at ∼5.5 mmol/l with a variable infusion of 20% glucose. The study was terminated after 8 h.

RESULTS—Both insulin analogs produced similar serum insulin levels (250–300 pmol/l) at ∼30 min and disappeared from serum after ∼4 h. Insulin aspart and lispro had similar effects on glucose and fat metabolism. Effects on carbohydrate metabolism (glucose uptake, glucose oxidation, and endogenous glucose production) peaked after ∼2–3 h and disappeared after ∼5–6 h. Effects on lipid metabolism (plasma free fatty acid, ketone body levels, and free fatty acid oxidation) appeared to peak earlier (at ∼2 h) and disappeared earlier (after ∼4 h) than the effects on carbohydrate metabolism.

CONCLUSIONS—We conclude that both insulin aspart and lispro are indistinguishable from each other with respect to blood levels and that they are equally effective in correcting abnormalities in carbohydrate and fat metabolism in patients with type 1 diabetes.