Consensus of experts from the Spanish Pharmacogenetics and Pharmacogenomics Society and the Spanish Society of Medical Oncology for the genotyping of DPYD in cancer patients who are candidates for treatment with fluoropyrimidines

5-Fluorouracil (5-FU) and oral fluoropyrimidines, such as capecitabine, are widely used in the treatment of cancer, especially gastrointestinal tumors and breast cancer, but their administration can produce serious and even lethal toxicity. This toxicity is often related to the partial or complete deficiency of the dihydropyrimidine dehydrogenase (DPD) enzyme, which causes a reduction in clearance and a longer half-life of 5-FU. It is advisable to determine if a DPD deficiency exists before administering these drugs by genotyping DPYD gene polymorphisms. The objective of this consensus of experts, in which representatives from the Spanish Pharmacogenetics and Pharmacogenomics Society and the Spanish Society of Medical Oncology participated, is to establish clear recommendations for the implementation of genotype and/or phenotype testing for DPD deficiency in patients who are candidates to receive fluoropyrimidines. The genotyping of DPYD previous to treatment classifies individuals as normal, intermediate, or poor metabolizers. Normal metabolizers do not require changes in the initial dose, intermediate metabolizers should start treatment with fluoropyrimidines at doses reduced to 50%, and poor metabolizers are contraindicated for fluoropyrimidines.

Consensus of experts from the Spanish Pharmacogenetics and Pharmacogenomics Society and the Spanish Society of Medical Oncology for the genotyping of DPYD in cancer patients who are candidates for treatment with fluoropyrimidines.

5-Fluorouracil (5-FU) and oral fluoropyrimidines, such as capecitabine, are widely used in the treatment of cancer, especially gastrointestinal tumors and breast cancer, but their administration can produce serious and even lethal toxicity. This toxicity is often related to the partial or complete deficiency of the dihydropyrimidine dehydrogenase (DPD) enzyme, which causes a reduction in clearance and a longer half-life of 5-FU. It is advisable to determine if a DPD deficiency exists before administering these drugs by genotyping DPYD gene polymorphisms. The objective of this consensus of experts, in which representatives from the Spanish Pharmacogenetics and Pharmacogenomics Society and the Spanish Society of Medical Oncology participated, is to establish clear recommendations for the implementation of genotype and/or phenotype testing for DPD deficiency in patients who are candidates to receive fluoropyrimidines. The genotyping of DPYD previous to treatment classifies individuals as normal, intermediate, or poor metabolizers. Normal metabolizers do not require changes in the initial dose, intermediate metabolizers should start treatment with fluoropyrimidines at doses reduced to 50%, and poor metabolizers are contraindicated for fluoropyrimidines.

Inadequate response to imatinib treatment in chronic myeloid leukemia due to a drug interaction with phenytoin.

Imatinib mesylate and the newer BCR-ABL tyrosine kinase inhibitors are the standard therapy for chronic myeloid leukemia. Although these are remarkably effective drugs, some mechanisms of resistance have been identified including drug-to-drug interactions. Here we present the case of a chronic myeloid leukemia patient with an inadequate response to imatinib due to concurrent phenytoin administration. Conspicuously low imatinib plasma trough levels were documented. Imatinib dose was increased from 400 to 800 mg with good response. In conclusion, drug-to-drug interactions should be ruled out in cases of resistance to tyrosine kinase inhibitor treatment. Potent inducers of cytochrome P450 isoenzyme CYP3A4, as phenytoin, could induce inadequate responses due to increased imatinib clearance and low imatinib trough plasma levels. Thus, this interaction should be avoided. When this is not possible, dose escalation of imatinib and measurement of plasma levels, if available, is recommended.

Impact of medication adherence on the effectiveness of deferasirox for the treatment of transfusional iron overload in myelodysplastic syndrome.

WHAT IS KNOWN AND OBJECTIVE: Regular blood transfusions in the management of myelodysplastic syndrome (MDS) often lead to iron overload. The main objective of this study was to evaluate the impact of medication adherence on the effectiveness of deferasirox for the treatment of transfusional iron overload in patients with MDS. Secondary objectives were to describe treatment effectiveness and safety in daily clinical practice. METHODS: A longitudinal, retrospective, observational study was carried out in a university hospital. The inclusion criteria were age over 18 years, MDS diagnosis and treatment with deferasirox for transfusion-dependent iron overload during the period of study (from January 2011 to April 2015). Treatment effectiveness was estimated by serum ferritin (SF), and adherence was measured by medication possession ratio (MPR). Clinically relevant analytical alterations during the treatment and reasons for treatment discontinuation were also assessed. RESULTS: Thirty-five patients were included in the study. Median SF at baseline was 1636 µg/L, and it decreased to 1399 µg/L during follow-up. The median adherence rate was 92%, although only 54·8% of the patients maintained deferasirox adherence ≥90% during the whole duration of treatment. Adherence rate was inversely correlated to SF (r = -0·288, P = 0·004). The median (p25, p75) duration of treatment was 11 (3·0, 37·8) months. The most common reasons for treatment discontinuation were renal toxicity (35%) and patient's death (25%). WHAT IS NEW AND CONCLUSION: Deferasirox's effectiveness, measured by the decrease in SF, was significantly better in adherent patients. The most frequent reason for treatment discontinuation was renal toxicity. Developing strategies to improve deferasirox treatment adherence and monitoring renal function in those patients should be key points in pharmaceutical care.