Effect of diltiazem on warfarin plasma protein binding

Previous work by Bloedow et al. evaluated the effect of warfarin on diltiazem binding. Unbound diltiazem remained constant (22.5 +/- 3.6 per cent) in the presence of warfarin. We studied 10 patients, 51 to 72 years old, who were receiving warfarin as an anticoagulant for valvular replacement, thrombosis, or embolus. Our study demonstrates that a single 120-mg oral diltiazem dose, sufficient to cause hemodynamic changes, does not displace warfarin from plasma binding sites.