Role of drug metabolism studies in the development of new drugs.

The efficacy and toxicity of drugs are closely related to the kinetics and metabolism of drugs. The metabolism of drugs is variable depending on individual, age, sex and species differences. Therefore, in this paper, the following strategies of drug metabolism studies on each phase of development of new drugs is discussed: 1. Early selection of drug candidates for the development of new drugs by a preliminary drug metabolism study. 2. Selection of a drug candidate for the repeated administration of drug toxicity study. 3. Drug metabolism studies on sex- and species-related differences in experimental animals. 4. Drug toxicity and metabolic activation of drug candidates. 5. In vitro and in vivo drug metabolism studies in humans. 6. Arrangement of drug metabolism and pharmacokinetic profile of drug candidate for the phase I study. 7. Role of pharmacokinetics and drug metabolism studies in the phase I study. 8. Pharmacokinetic and metabolic studies for the development of chiral drugs. 9. Approach to drug design from the viewpoint of drug metabolism studies. In conclusion, performance of drug metabolism studies starting from the early stage of drug development is a powerful and useful tool to increase the efficiency and to minimize the period and cost for the development of new drugs.