The influence of barbiturates on coumarin plasma levels and prothrombin response.

Wide individual variations in response to drugs is a common clinical problem, and is especially evident with coumarin anticoagulant therapy (1-3). A possible contributing factor to such variations could be the influence of another presumably unrelated drug upon the response to the coumarin anticoagulant. Reports from several laboratories (4-7) indicate that barbiturates can reduce the prothrombin response to coumarin anticoagulants. This report presents initial results of studies designed to determine the manner by which barbiturates alter the response to coumarins in man, guinea pig and dog.