Introduction: Secondary monotherapy failure in diabetes mellitus type 2 occurs early in the course of disease. Choosing the optimal combination therapy depends on the primary pathogenic mechanism. Evaluation of the residual beta cell function is of primary importance in deciding whether insulin should be included in the combination therapy.
Objective: To investigate the influence of standard meal test and homeostasis model assessment (HOMA-B) index, as markers of residual insulin secretion, on the efficacy of two different therapeutic strategies in secondary sulphonylurea (SU) failure.
Methods: In the group of thirty subjects with diabetes type 2, metabolic syndrome and secondary SU failure, metformin (MET) was added for the following six months. In the group of 30 subjects with diabetes type 2, secondary SU failure, with no metabolic syndrome, insulin (INS) was added for the same period. During the six-month follow-up period, fasting, postprandial, mean daily blood glucose and glycosylated haemoglobin (HbA1C) were evaluated. Fasting and meal stimulated C-peptide (CP) and insulin levels were measured at the beginning; absolute and relative increase of CP (delta CP, delta CP%), and HOMA-B were calculated. Correlation between CP secretion and HOMA-B at the beginning and glycaemic control after six months of therapy were evaluated by using Pearson correlation coefficient.
Results: Glycaemic control after six months was significantly improved in both therapeutic combinations (p < 0.01). However, target values were not met in either group. Stimulated CP levels correlated best with all the parameters of glycaemic control in the group SU+MET (r -0.479 to -0.791; p < 0.01), and in the group SU+INS (r 0.382 to 0.635; p < 0.01). HOMA-B correlated only with HbA1C in the SU+MET group (r = -0.382; p < 0.05).
Conclusion: Clinical diagnosis of metabolic syndrome and evaluation of residual insulin secretion are necessary in choosing the best combination therapy in secondary SU failure in subjects with type 2 diabetes. Stimulated standard meal CP level is a clinically useful marker of residual insulin secretion.