Factors affecting drug metabolism: internal factors

Abstract

Drugs can be metabolised by many different pathways (see chapter 1) and many factors can determine which pathway is used by which drug and to what extent a particular drug is biotransformed by a particular pathway. These factors range from the species of organism studied to the environment in which that organism lives. In order to discuss this topic, the factors affecting drug metabolism will be split into internal (i.e. physiological and pathological) factors (discussed in this chapter) and external factors (i.e. diet and environment) (discussed in chapter 5). These are, of course, purely arbitrary divisions and much interaction exists between the various factors (cf. hormonal, sex and age influences) — such interactions will be pointed out where they are important. The factors discussed here are also not an exhaustive list and other factors that play a role in controlling drug biotransformation will be found in the Further Reading section at the end of chapter 5. The factors to be discussed here are:

• internal

  • species

  • genetic (strain)

  • age

  • sex

  • hormones

  • disease

• external

  • diet

  • environment

Each of these factors will be examined in turn giving examples of the differences seen. Internal factors are discussed in this chapter, while external factors are discussed in chapter 5.