Abstract
Although the expenditure for new drug development by the pharmaceutical industry has been increasing in recent years, the number of new drugs approved has remained unchanged or has been gradually decreasing. For the effective development of new drugs, attrition rates of drug candidates should be reduced. In 1991, major causes of the attrition were ADME (absorption, distribution, metabolism and excretion) (about 40%), efficacy (about 30%), and safety issues (about 25%). In 2000, the causes were ADME (less than 10%), efficacy (about 30%), and safety issues (about 30%). Between 1991 and 2000, the attrition caused by ADME issues decreased drastically, but that caused by efficacy and safety issues did not change. To improve this situation, exploratory clinical studies including microdose and exploratory IND (Investigational New Drug) studies proposed in EU and USA, respectively, have been started at the late 1990s and the early 2000s. This commentary reviews the current situation of the exploratory clinical studies and the recent trend of pharmacokinetic studies in new drug development.
