[C-peptide levels in secondary sulfonylurea resistant diabetics].

In the presence of clinical features of secondary drug failure--even after reeducation on diet and intensive control of patients--is difficult to make a decision to switch on insulin. Therefore the serum C-peptide concentrations were assessed in order to get supporting data. From 35 patients with suspected secondary drug failure the therapy of 11 patients was continued with insulin, 24 patients remained on glibenclamide therapy. The decision based on clinical criteria. All of the patients were studied in i.v. glucagon test and with a test meal to evaluate their basal and stimulated serum C-peptide concentrations. There were only three patients with subnormal basal C-peptide (< or = 0.30 nmol/l), on the other hand nine patients had lower post-glucagon serum C-peptide level than 0.60 nmol/l. The basal and stimulated C-peptide concentrations from i.v. glucagon test and test-meal indicated the need of insulin therapy with a sensitivity of 81.8 percent and with specificity of 70.8 percent. The further glibenclamide treatment on the basis of C-peptide concentrations in 89.5 percent of cases could be accurately established. The statistical analysis showed that the glucagon-stimulated C-peptide concentration was the most characteristic feature to discriminate the patients in order to make a decision on the further diabetes therapy.