Effect of CYP2C9 *11/*11 Genotype on Initial and Long-Term Warfarin Dose Requirement and Therapeutic Response

The warfarin dose requirement and therapeutic response of a 42-year-old African–American male with genotype CYP2C9 *11/*11, VKORC1 -1639GG and CYP4F2 433Val/Val anticoagulated for ischemic stroke is described herein. Warfarin was dosed according to the institution’s personalized medicine program recommendations of a 10 mg mini-load dose, followed by dose decreases to 4–6 mg/day through discharge. Stable international normalized ratio was achieved after eight doses, with good overall long-term maintenance of therapeutic international normalized ratio over several years with warfarin doses of 3.1–4.3 mg/day. This case report sheds further light on the clinical impact of CYP2C9 *11/*11 on warfarin dose requirements, short- and long-term treatment response and practical considerations for warfarin management in suspected carriers of rare variant CYP2C9 alleles.