Chronic kidney disease (CKD) is a major health problem worldwide and, in Spain, it is present in 15.1% of individuals. CKD is frequently associated with some comorbidities and patients need to be prescribed multiple medications. Polypharmacy increases the risk of adverse drug reactions (ADRs). There are no published studies evaluating the prevalence of potential drug–drug interactions (pDDIs) among CKD patients in any European country. This study was aimed to determine the prevalence, pattern, and factors associated with pDDIs among CKD patients using a drug interactions program. An observational cross-sectional study was carried out at Plasencia Hospital, located in Spain. Data were collected among patients with CKD diagnoses and pDDIs were assessed by the Lexicomp® Drug Interactions platform. Data were obtained from 112 CKD patients. A total number of 957 prescribed medications were acknowledged, and 928 pDDIs were identified in 91% of patients. Age and concomitant drugs were significantly associated with the number of pDDIs (p < 0.05). According to the results, the use of programs for the determination of pDDIs (such as Lexicomp®) is recommended in the clinical practice of CKD patients in order to avoid serious adverse effects, as is paying attention to contraindicated drug combinations.

Background: A promoter variable number tandem repeat polymorphism (pVNTR) of CYP2C9 is described with three types of fragments: short (pVNTR-S), medium (pVNTR-M) and long (pVNTR-L). The pVNTR-S allele reduces the CYP2C9 mRNA level in the human liver, and it was found to be in high linkage disequilibrium (LD) with the CYP2C9*3 allele in a White American population. The aim of the present study is to determine the presence and frequency of CYP2C9pVNTR in a Spanish population, as well as analyzing whether the pVNTR-S allele is in LD with the CYP2C9*3 allele in this population. Subjects and Methods: A total of 209 subjects from Spain participated in the study. The CYP2C9 promoter region was amplified and analyzed using capillary electrophoresis. Genotyping for CYP2C9*2 and *3 variants was performed using a fluorescence-based allele-specific TaqMan allelic discrimination assay. Results: The frequencies of CYP2C9pVNTR-L, M and S variant alleles are 0.10, 0.82 and 0.08, respectively. A high LD between CYP2C9pVNTR-S and CYP2C9*3 variant alleles is observed (D’ = 0.929, r2 = 0.884). Conclusion: The results from the present study show that both CYP2C9pVNTR and CYP2C9*3 are in a high LD, which could help to better understand the lower metabolic activity exhibited by CYP2C9*3 allele carriers. These data might be relevant for implementation in the diverse clinical guidelines for the pharmacogenetic analysis of the CYP2C9 gene before treatment with different drugs, such as non-steroidal anti-inflammatory drugs, warfarin, phenytoin and statins.