Abstract

Diabetic patients often have a kidney or pancreas allograft requiring cyclosporine A (CsA) to prevent transplant rejection. These patients usually take p.o. hypoglycemic agents to control their diabetes. Because of the reported adverse effects of CsA on glucose metabolism as well as its potential use in Type II diabetics, we were interested in evaluating the in vivo effect of CsA on the activity of p.o. hypoglycemic agents. We also wanted to determine if tolbutamide produced any adverse effects on the pharmacokinetics of CsA. Male, Holtzman rats were administered CsA (p.o.) followed 1 hr later with the hypoglycemic agent. Two hours later, blood samples were obtained to determine blood glucose levels. Animals treated with CsA alone produced a significant hyperglycemia. The hypoglycemic effects produced by tolbutamide and glyburide were inhibited in animals treated concomitantly with CsA. This inhibitory effect was not observed during the first 3 hr of CsA-treatment, could not be overcome by increasing the dose of the hypoglycemic agent and occurred using small doses. CsA did not, however, interfere with the activity of exogenous NPH insulin. Tolbutamide was found to have no effect on the acute pharmacokinetics of CsA. The distribution of CsA was similar to controls in all tissues studied except the liver in which CsA levels were less in tolbutamide-treated animals. These studies demonstrate that CsA interferes with the effects of p.o. hypoglycemic agents and, therefore, blood glucose levels should be monitored closely in Type II diabetic patients taking combinations of these drugs.