Both warfarin and non-steroidal anti-inflammatory drugs are metabolised by cytochrome P450 (CYP2C9 enzyme). There are three variants of the CYP2C9 gene (CYP2C9*1, *2, and *3) and in European populations about 80% of people are homozygous for the CYP2C9*1 allele. The *2 and *3 alleles are found in 11% and 5–7% respectively. The *2 variant is associated with about 12% of …