['Omeprazole-induced acute interstitial nephritis (OIAIN) is a rare adverse event. It is unknown if this is an idiosyncratic immune mediated reaction or if it relates to direct drug toxicity. Individuals who are homozygous for the variant alleles of CYP2C19 are poor metabolizers of omeprazole and have a greater exposure to the drug. The aim of this study was to determine the prevalence of the CYP2C19 poor metabolizer genotype and phenotype in patients with OIAIN.', 'Twenty patients were genotyped for the CYP2C19 variant alleles (2, 681G>A and 3, 636G>A) by RFLP-PCR analysis and eighteen phenotyped for CYP2C19 metabolizer status.', 'The frequency of the CYP2C19 2 allelic variant was 12.5%, no 3 allelic variants were detected and no patient was a homozygous variant genotype. This was not different from the expected frequency. 33% of subjects were phenotypically CYP2C19 poor metabolizers.'] Is omeprazole-induced acute interstitial nephritis related to CYP2C19 genotype or CYP2C19 phenotype?