Table 1: Selected examples of drugs with relevant pharmacogenomic biomarkers and context of use.

DrugsPharmacogenomic biomarker or variant alleleResponse phenotypeRegulatory decision and/or clinical recommendation

AbacavirHLA-B*5701Hypersensitivity reactionsFDA and EMA warn of increased risk in patients with HLA-B*5701. Genetic screening recommended before starting therapy. Patients tested positive should not receive abacavir.
Azathioprine and 6-mercaptopurineDefective TPMT alleles
(e.g. TMPT*2)
MyelosuppressionIncreased risk for myelotoxicity in homozygotes treated with conventional doses. FDA recommends genetic testing prior to treatment.
CarbamazepineHLA-B*1502Stevens-Johnson syndrome (SJS) and toxic epidermal necrolysis (TEN)FDA warns of increased risk for increased risk of SJS and TEN in patients with HLA-B*1502. Patients from high-risk regions (e.g., Southeast Asia) should be screened for HLA-B*1502 before starting carbamazepine.
Cetuximab and panitumumabEGRF, KRAS EfficacyWith clinical benefit limited to patients with EGRF-positive tumors, both chemotherapeutic drugs are indicated for EGRF-expressing colorectal cancer with wild-type KRAS. They may be ineffective in patients with tumors expressing KRAS mutation. Mandatory testing required.
CodeineDuplicated or amplified CYP2D6 allelesCNS depressionFDA warning regarding patients who are ultrarapid metabolizers secondary to the CYP2D6*2XN genotype would have much higher morphine concentration, and at increased risk for CNS symptoms related to overdose, even when treated with standard doses.
ClopidogrelDefective CYP2C19 alleles (e.g. CYP2C19*2, CYP2C19*3)EfficacyFDA warns of possible reduced effectiveness in CYP2C19 homozygotes.
CrizotinibALK EfficacyMandatory testing required by the FDA to confirm the presence of lymphoma kinase (ALK) mutation prior to drug use.
GefitinibEGRF EfficacyApproved by EMA for treatment of EGRF-expressing tumors.
ImatinibBCR-ABL translocationEfficacyMandatory testing required by the FDA for confirmation of disease and selection of patients for which the drug is indicated.
IrinotecanUGT1A1*28 NeutropeniaFDA recommends dosage reduction by one level in homozygotes.
MaravirocCCR-5 EfficacyFDA and EMA approved indication is only for HIV infection with CCR-5-tropic-HIV-1.
TrastuzumabHER2 EfficacyFDA and EMA require mandatory testing for HER2-overexpressing cancers prior to treatment.
VemurafenibBRAF V600E mutationEfficacyFDA requires mandatory testing for the mutation prior to drug use.
WarfarinCYP2C9  
VKORC1
Efficacy and toxicity (bleeding)FDA provides dose recommendations according to CYP2C9 and VKORC1 genotypes.