Pharmacogenetics and pharmacogenomics have been widely recognized as fundamental 
steps toward personalized medicine. They deal with genetically determined 
variants in how individuals respond to drugs, and hold the promise to 
revolutionize drug therapy by tailoring it according to individual genotypes.The 
clinical need for novel approaches to improve drug therapy derives from the high 
rate of adverse reactions to drugs and their lack of efficacy in many 
individuals that may be predicted by pharmacogenetic testing.Significant 
advances in pharmacogenetic research have been made since inherited differences 
in response to drugs such as isoniazid and succinylcholine were explored in the 
1950s. The clinical utility and applications of pharmacogenetics and 
pharmacogenomics are at present particularly evident in some therapeutic areas 
(anticancer, psycotrophic, and anticoagulant drugs).Recent evidence derived from 
several studies includes screening for thiopurine methyl transferase or uridine 
5'-diphosphoglucuronosyl-transferase 1A1 gene polymorphisms to prevent 
mercaptopurine and azathioprine or irinotecan induced myelosuppression, 
respectively. Also there is a large body of information concerning cytochrome 
P450 gene polymorphisms and their relationship to drug toxicity and response. 
Further examples include screening the presence of the HLA-B*5701 allele to 
prevent the hypersensitivity reactions to abacavir and the assessment of the 
human epidermal growth factor receptor (HER-2) expression for trastuzumab 
therapy of breast cancer or that of KRAS mutation status for cetuximab or 
panitumumab therapy in colorectal cancer.Moreover, the application of 
pharmacogenetics and pharmacogenomics to therapies used in the treatment of 
osteoarticular diseases (e.g. rheumatoid arthritis, osteoporosis) holds great 
promise for tailoring therapy with clinically relevant drugs (e.g. 
disease-modifying antirheumatic drugs, vitamin D, and estrogens). Although the 
classical candidate gene approach has helped unravel genetic variants that 
influence clinical drug responsiveness, gene-wide association studies have 
recently gained attention as they enable to associate specific genetic variants 
or quantitative differences in gene expression with drug response.Although 
research findings are accumulating, most of the potential of pharmacogenetics 
and pharmacogenomics remains to be explored and must be validated in prospective 
randomized clinical trials.The genetic and molecular foundations of personalized 
medicine appear solid and evidence indicates its growing importance in 
healthcare.