Background:

The efficacy of atypical antipsychotics, such as olanzapine, clozapine, risperidone, quetiapine and ziprasidone in treating a broad spectrum of symptoms in schizophrenia as well as their lower likelihood of extrapyramidal symptoms have led to an increased use of these substances. However there is an ongoing debate whether treatment with atypical antipsychotics is associated with a higher risk for metabolic abnormalities. The FDA stated in 2003 that all atypical antipsychotics increase the risk for glucose abnormalities. For olanzapine many, but not all studies report an increased risk for the development of metabolic abnormalities, such as glucose intolerance, insulin-resistance and consequentially NIDDM (Non-Insulin-Dependent-Diabetes Mellitus). Ziprasidone on the other hand seems to be associated with a more favorable metabolic safety profile.Glucose intolerance and insulin resistance being risk factors for the development of NIDDM and cardiovascular disease, the exact determination of putative effects of atypical antipsychotics on insulin sensitivity and resistance is of great need. An innovative technique, microdialysis, allows for the measurement of various analytes in the interstitial space, i.e. to assess insulin sensitivity directly at the responsible compartment, which is the human skeletal muscle. With the use of microdialysis it is possible to determine the arterial to interstitial gradient, a suitable marker for plasma glucose extraction of peripheral tissue, and thus detect insulin resistance directly at the site of insulin action.

Aim of the study:

To compare the effects of treatment with the atypical antipsychotics olanzapine and ziprasidone in steady-state conditions on the arterial to interstitial skeletal muscle gradient for glucose in human skeletal muscle during euglycaemic hyperinsulinaemic clamp conditions in male healthy volunteers.

Study design:

Open, randomized, mono-center study.

Materials and methods:

Healthy volunteers will undergo euglycaemic hyperinsulinaemic clamp and microdialysis before and after administration of 10mg olanzapine or 80mg ziprasidone during 10 days.

Study population:

15 healthy volunteers will participate in each arm of the study, summing up to a total of 30 participants.

Main outcome variable:

The arterial to interstitial skeletal muscle glucose gradient before and during euglycaemic hyperinsulinaemic clamp conditions, before and after administration of 10mg olanzapine or 80mg ziprasidone under steady-state conditions.