Table 2.

Recommendations for therapy based on genotype in CPIC guideline.

Drugs	Genotype	Therapeutic recommendation
Allopurinol	HLA-B*58:01	Allopurinol is contraindicated.
Carbamazepine Oxcarbazepine	HLA-B*15:02 positive	If a patient is carbamazepine- or oxcarbazepine-naïve, do not use both drugs. Optional If a patient has previously used carbamazepine or oxcarbazepine consistently for longer than 3 months without the incidence of cutaneous adverse reactions, cautiously consider the use of carbamazepine or oxcarbazepine.
Carbamazepine	HLA-B*15:02 negative and HLA-A*31:01 positive	If a patient is carbamazepine-naïve and alternative agents are available, do not use carbamazepine. Optional If the patient is carbamazepine-naïve and alternative agents are unavailable, consider the use of carbamazepine with increased frequency of clinical monitoring. Discontinue therapy at the first evidence of a cutaneous adverse reaction. If a patient has previously used carbamazepine consistently for longer than 3 months without the incidence of cutaneous adverse reactions, cautiously consider the use of carbamazepine.
Phenytoin Fosphenytoin	HLA-B*15:02 positive	If the patient is phenytoin naïve, do not use phenytoin/fosphenytoin.
	HLA-B*15:02 negative
	CYP2C9 intermediate metabolizer (*1/*3, *2/*2)	Consider a 25% reduction of the recommended starting maintenance dose. Subsequent maintenance doses should be adjusted according to therapeutic drug monitoring and response.
	CYP2C9 poor metabolizer (*2/*3, *3/*3)	Consider a 50% reduction of the recommended starting maintenance dose. Subsequent maintenance doses should be adjusted according to therapeutic drug monitoring and response.

CPIC, Clinical Pharmacogenetics Implementation Consortium.