MedGen

Capecitabine is a chemotherapeutic agent and a member of the fluoropyrimidine group of substances. It is a prodrug of 5-fluorouracil and mainly used to treat solid tumors, such as colorectal, breast and aerodigestive cancers. Dihydropyrimidine dehydrogenase (DPD, encoded by the DPYD gene) is the rate-limiting enzyme for fluoropyrimidine metabolism and is therefore responsible for the detoxification of these types of drugs. Patients who are homozygous for variants in DPYD that lead to a non-functional protein, such as *2A or *13, have a high risk of severe or fatal drug toxicities and may benefit from receiving an alternative chemotherapeutic drug. Patients heterozygous for these variants also have an increased risk for drug toxicities, and reduced dosing is recommended for these individuals. Guidelines regarding the use of pharmacogenomic tests in dosing for capecitabine have been published in Clinical Pharmacology and Therapeutics by the Clinical Pharmacogenetics Implementation Consortium (CPIC) and are available on the PharmGKB website. [from PharmGKB]

Dihyropyrimidine dehydrogenase deficiency (DPYDD) shows large phenotypic variability, ranging from no symptoms to a convulsive disorder with motor and mental retardation in homozygous patients. In addition, homozygous and heterozygous mutation carriers can develop severe toxicity after the administration of the antineoplastic drug 5-fluorouracil (5FU), which is also catabolized by the DPYD enzyme. This is an example of a pharmacogenetic disorder (Van Kuilenburg et al., 1999). Since there is no correlation between genotype and phenotype in DPD deficiency, it appears that the deficiency is a necessary, but not sufficient, prerequisite for the development of clinical abnormalities (Van Kuilenburg et al., 1999; Enns et al., 2004). [from OMIM]

Tegafur is a chemotherapeutic agent and a member of the fluoropyrimidine group of substances. It is a prodrug of 5-fluorouracil and mainly used to treat solid tumors, such as colorectal, breast and aerodigestive cancers. Dihydropyrimidine dehydrogenase (DPD, encoded by the DPYD gene) is the rate-limiting enzyme for fluoropyrimidine metabolism and is therefore responsible for the detoxification of these types of drugs. Patients who are homozygous for variants in DPYD that lead to a non-functional protein, such as *2A or *13, have a high risk of severe or fatal drug toxicities and may benefit from receiving an alternative chemotherapeutic drug. Patients heterozygous for these variants also have an increased risk for drug toxicities, and reduced dosing is recommended for these individuals. Guidelines regarding the use of pharmacogenomic tests in dosing for tegafur have been published in Clinical Pharmacology and Therapeutics by the Clinical Pharmacogenetics Implementation Consortium (CPIC) and are available on the PharmGKB website. [from PharmGKB]