Different responses, in terms both of efficacy and toxicity, are commonly 
observed for any drug administered to apparently homogeneous groups of patients. 
It is estimated that adverse drug reactions (ADRs) cause 3-6% of all 
hospitalizations, accounting for 5% to 9% of hospital admission costs. The skin 
is often involved in ADRs and although most cutaneous ADRs have a favorable 
course, they may present as severe adverse cutaneous drug reactions (SCARs), 
such as Stevens-Johnson syndrome, toxic epidermal necrolysis, drug reaction with 
eosinophilia and systemic symptoms (also referred to as drug-induced 
hypersensitivity syndrome), and acute generalized exanthematous pustulosis. 
SCARs are associated with significant mortality and require prompt diagnosis and 
adequate treatment. Pharmacogenetics studies individual variants in the DNA 
sequence associated with drug efficacy and toxicity, allowing prescription of a 
drug to patients expected to benefit from it, and excluding from treatment those 
who are at risk of developing ADRs. Pharmacogenetics already achieved several 
important results in the prevention of SCARs, and pharmacogenetic testing is now 
recommended by regulatory agencies before administration of abacavir and 
carbamazepine, leading to reduced incidence of SCARs. In this review, the 
pharmacogenetic associations of SCARs that have been validated in independent, 
case-control association studies will be presented. By familiarizing with 
principles of pharmacogenetics, dermatologists should be able to correlate 
specific cutaneous ADR phenotypes to the underlying genotype, thus contributing 
to better drug safety and facilitating drug discovery, development and approval.