Table 1.

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

Drugs	Pharmacogenomic biomarker or variant allele	Response phenotype	Regulatory decision and/or clinical recommendation
Abacavir	HLA-B∗5701	Hypersensitivity reactions	FDA 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-mercaptopurine	Defective TPMT alleles (e.g. TMPT∗2)	Myelosuppression	Increased risk for myelotoxicity in homozygotes treated with conventional doses. FDA recommends genetic testing prior to treatment.
Carbamazepine	HLA-B∗1502	Stevens-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 panitumumab	EGRF, KRAS	Efficacy	With 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.
Codeine	Duplicated or amplified CYP2D6 alleles	CNS depression	FDA 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.
Clopidogrel	Defective CYP2C19 alleles (e.g. CYP2C19∗2, CYP2C19∗3)	Efficacy	FDA warns of possible reduced effectiveness in CYP2C19 homozygotes.
Crizotinib	ALK	Efficacy	Mandatory testing required by the FDA to confirm the presence of lymphoma kinase (ALK) mutation prior to drug use.
Gefitinib	EGRF	Efficacy	Approved by EMA for treatment of EGRF-expressing tumors.
Imatinib	BCR-ABL translocation	Efficacy	Mandatory testing required by the FDA for confirmation of disease and selection of patients for which the drug is indicated.
Irinotecan	UGT1A1∗28	Neutropenia	FDA recommends dosage reduction by one level in homozygotes.
Maraviroc	CCR-5	Efficacy	FDA and EMA approved indication is only for HIV infection with CCR-5-tropic-HIV-1.
Trastuzumab	HER2	Efficacy	FDA and EMA require mandatory testing for HER2-overexpressing cancers prior to treatment.
Vemurafenib	BRAF V600E mutation	Efficacy	FDA requires mandatory testing for the mutation prior to drug use.
Warfarin	CYP2C9   VKORC1	Efficacy and toxicity (bleeding)	FDA provides dose recommendations according to CYP2C9 and VKORC1 genotypes.