CONCLUSION:
(1) Itraconazole decreased simvastatin metabolism in vitro in both human and rat liver microsomes. Itraconazole had no effect on pravastatin metabolism.

(2) Fenofibrate and niacin had decreased pravastatin metabolism in both human and rat liver microsomes.

(3) No simvastatin was detected in the rat plasma samples; therefore, the effect of grapefruit juice on the pharmacokinetics on statins is unsure.

FURTHER STUDY:
There are various possible reasons that the in vivo study was not successful in determining the effect of grapefruit juice on anti-cholesterol drugs. The rats may have a higher metabolic rate than expected. As a result, the elimination of the medication out of their systems would have occurred at a faster rate. The drug dosage given to the rats may not have been high enough to cause a measurable effect.

Blood plasma samples were taken and tested to measure drug concentrations. Although there was no simvastatin detected in the blood samples, the drug may be detectable in other fluids. Urine samples were also collected during the study and will be studied to determine whether there is any detectable concentration of simvastatin. Further studies are required to determine whether or not grapefruit juice has an effect on anti-cholesterol medications.