Biotransformation of insulin glargine after subcutaneous injection in healthy subjects

Objective: It is important to establish pharmacokinetic or pharmacodynamic differences between novel insulin analogues and human insulin. This study examined the primary metabolic degradation products of insulin glargine (LANTUS*) in humans. Design: In this single dose, open-label study, insulin glargine was administered subcutaneously at a dose of 0.6 IU/kg; placebo was administered to one control subject. Patients: Four healthy male subjects, plus one control subject, aged 18-50 years were enrolled in this study. Measurements: Following insulin glargine administration, blood glucose levels were clamped at the subjects' fasting concentration for 6 h and the amount of 20% glucose infused to maintain this baseline concentration was recorded. Metabolite profiling was performed in plasma and injection site tissue using HPLC and radioimmunoassay (RIA). Pharmacokinetics were evaluated by RIA of serum and plasma immunoreactive insulin levels. The primary pharmacodynamic measure was the glucose infusion rate (GIR). Safety was evaluated by measuring blood glucose concentrations during the clamp and adverse events were observed by the investigator or reported by the subject. Results: Metabolic profiling revealed a clear pattern: insulin glargine is metabolised by sequential cleavage at the carboxy terminus of the B chain, to yield products M1 and M2, which are both structurally similar to human insulin. These degradation products are present both at the injection site and in plasma. Conclusion: Thus, during treatment with a subcutaneous injection of insulin glargine, metabolic degradation is likely to be initiated at the injection site and continued within the circulatory system.