Pfizer/IVGTT/Ziprasidone/Olanzapine

This proposal aims to use a well-characterized procedure, the modified Frequently Sampled Intravenous Glucose Tolerance Test (FSIGTT), to characterize the glucoregulatory effects of the two most commonly prescribed atypical antipsychotic medications, ziprasidone and olanzapine, in comparison to the conventional antipsychotic haloperidol. Abnormalities in peripheral glucose regulation and type 2 diabetes can occur more commonly in individuals with schizophrenia than in healthy subjects or in other psychiatric conditions. While abnormalities in glucose regulation were first reported in schizophrenia prior to the introduction of antipsychotic medications, antipsychotic treatment may contribute significantly to abnormalities in glucose regulation. Recently, the adverse effect of antipsychotic medications on systemic glucose regulation has received increased attention as investigators noted prominent adverse glucoregulatory effects associated with certain newer antipsychotic medications. Abnormal glucose regulation and new-onset type 2 diabetes have been reported during clozapine and olanzapine treatment. Complicating the study of antipsychotic-induced changes in glucose regulation, increased adiposity can decrease insulin sensitivity, and antipsychotics can increase adiposity and body mass index (BMI). However, abnormal glucose regulation and type 2 diabetes can occur during clozapine treatment in the absence of weight gain, suggesting that changes in glucose regulation can occur independent of drug-induced increases in BMI. Consistent with this, our preliminary studies indicate that important effects of clozapine and olanzapine on glucose regulation are not accounted for by differences in BMI. This proposal will compare the effects of olanzapine, ziprasidone and haloperidol on well-defined measures of glucose regulation. This proposal specifically hypothesizes that olanzapine treatment will be associated with decreases in insulin sensitivity (SI), without effects on insulin secretion. Treatment-related effects on glucose effectiveness (SG) will be explored.