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Enhanced anticoagulant effect of coumarin derivatives induced by doxycycline coadministration
Objective:
To report two cases of enhanced oral anticoagulant effect induced by doxycycline coadministration.
Design:
Case report.
Setting:
University teaching hospital.
Patients:
Two patients on chronic oral anticoagulation therapy who presented with severe bleeding and marked impairment in blood coagulation tests shortly after the initiation of doxycycline therapy.
Discussion:
The literature concerning the possible effects of tetracyclines on hemostasis with or without antecedent anticoagulation therapy is reviewed and the speculated mechanisms for such an interaction are discussed.
Conclusions:
The administration of tetracyclines such as doxycycline to patients on chronic oral anticoagulation therapy may be associated with a marked enhancement in anticoagulant effect. In such patients the prothrombin ratio should be closely monitored and the anticoagulant dosage adjusted accordingly.