Coumarin resistance: a diagnostic and therapeutic approach

Resistance to coumarin anticoagulants in two black patients was established. The resistance appears to be of the pharmacodynamic type since high doses of the coumarin drugs (with accompanying high plasma concentrations) were needed to achieve therapeutic prothrombinemia. A pharmacokinetic mechanism for the resistance was ruled out. This phenomenon has no ethnic uniqueness as exemplified by these cases and two earlier reports. A brief review of the problem is presented, with an approach for establishing the type of resistance and a plan for patient management.