ClarkiePharma, a drug development firm, contracts with a Japanese researchorganization to investigate the potential for drug interactions for their new antifungal compound. This compound is primarily metabolized by CYP2C19, withan average drug clearance in Caucasian males of 120 mL/minute. The researchersperform a study in 16 Japanese males, finding a baseline drug clearance of 50 mL/minute. With the addition of ketoconazole, clearance drops to approx 38 mL/minute, and tests of bioequivalence do not reveal a drug interaction. When thedrug is put into Phase II studies in humans (Caucasians and African Americans)with fungal infections, addition of ketoconazole results in a substantial increasein the investigational drug exposure and significant toxicity.