Effect of age and sex on warfarin dosing.

OBJECTIVE: We examined the potential effect of sex and age on warfarin dosing in ambulatory adult patients. METHODS: We conducted a retrospective chart review of patients attending an anticoagulation clinic. We included patients anticoagulated with warfarin for atrial fibrillation or venous thromboembolism who had a therapeutic international normalized ratio of 2-3 for 2 consecutive months. We excluded patients who had been on any drug that is known to have a major interaction with warfarin, smokers, and heavy alcohol consumers. Out of 340 screened medical records, 96 met the predetermined inclusion criteria. The primary outcome assessed was warfarin total weekly dose (TWD). RESULTS: There was a statistically significant difference in the TWD among the ages (P<0.01); older patients required lower doses. However there was no statistically significant difference in the TWD between sexes (P=0.281). CONCLUSION: Age was found to have a significant effect on warfarin dosing. Even though women did require a lower TWD than men, this observation was not statistically significant.