ABSTRACT
A subgroup of patients receiving a drug may fail to respond to the medication or develop
adverse reactions. Such interindividual variability in drug response has a major impact in
both clinical practice and drug development. Several host factors, including the patient’s
age, gender, smoking habit, alcohol consumption, renal and liver function, and disease
factors are likely to influence drug response. In addition to this, genetic factors may
also be important (1-4). This chapter reviews the evolving concepts and potential appli-
cations of such genetic factors, a field of study termed pharmacogenetics, and more
recently pharmacogenomics (5), in gastrointestinal and liver diseases. Much of the
focus of pharmacogenetics is on single-nucleotide polymorphisms (SNPs) which are the
most common source of variation in the human genome, occurring at approximately 1
in 1000 base pairs (6).
