An open, randomized, four-phased crossover study using 4 mg of pitavastatin or 20 mg of atorvastatin was performed to compare their efficacy and safety, especially regarding plasma levels of coenzyme Q10 (CoQ10) in 19 Japanese patients with heterozygous familial hypercholesterolemia. Pitavastatin and atorvastatin caused significant and almost comparable reductions in serum levels of total cholesterol (-35.4 vs. -33.8%), low-density lipoprotein cholesterol (-42.8 vs. -40.7%), and triglyceride (-26.1 vs. -29.4%), and significantly increased serum levels of high-density lipoprotein cholesterol (12.1 vs. 11.4%). Under these conditions, plasma levels of CoQ10 were reduced by atorvastatin (-26.1%, P=0.0007) but not by pitavastatin (-7.7%, P=0.39), although no adverse events or abnormalities of liver and muscle enzyme were observed after either statin treatment. It remains to be seen whether the observed changes in CoQ10 levels are related to the long-term safety of this drug.