Anticoagulant therapy, oral, monitoring

Fairweather RB, Ansell J, van den Besselaar AM, et al. College of American Pathologists Conference XXXI on laboratory monitoring of anticoagulant therapy Laboratory monitoring of oral anticoagulant therapy. Arch Pathol Lab Med 1998 122 768-781. 

Andrew M, Marzinotto V, Adams M, Cimini C. LaDuca F. Monitoring of oral anticoagulant therapy in pediatric patients using a new microsample PT device. Blood 1995 86(Suppl) 863. 

The prothrombin time (PT), as proposed by Quick, is the most commonly performed coagulation function test. It is used to monitor oral anticoagulant therapy and also as a preoperative screening test to warn of possible bleeding risk in patients with a personal or family history of bleeding (Table 36-2). Measured clotting times are extremely dependent on the animal and tissue source and the quality of the thromboplastin used. Variability can be expected because of the assay s dependence on the number of tissue factor molecules and the quantity of... 

Ansell JE. Empowering patients to monitor and manage oral anticoagulation therapy. JAMA 1999 281 182-183. 

The INR is monitored when the client is receiving oral anticoagulant therapy. 

PT is not directly monitored for oral anticoagulant therapy but will be elevated in clients receiving oral anticoagulants. 

A number of laboratory tests are available to measure the phases of hemostasis described above. The tests include platelet count, bleeding time, activated partial thromboplastin time (aPTT or PTT), prothrombin time (PT), thrombin time (TT), concentration of fibrinogen, fibrin clot stabifity, and measurement of fibrin degradation products. The platelet count quantitates the number of platelets, and the bleeding time is an overall test of platelet function. aPTT is a measure of the intrinsic pathway and PT of the extrinsic pathway. PT is used to measure the effectiveness of oral anticoagulants such as warfarin, and aPTT is used to monitor heparin therapy. The reader is referred to a textbook of hematology for a discussion of these tests. 

Pharmacokinetics Streptokinase therapy is instituted within 4 hours of a myocardial infarction and is infused for 1 hour. Its ti/2 is less than a half-hour. Thromboplastin time is monitored and maintained at two to five times control value. On discontinuation of treatment, either heparin or oral anticoagulants may be administered. 

ANTICOAGULANTS-ORAL CEPHALOSPORINS Certain cephalosporins (cefaclor, cefixime, ceftriaxone) may t efficacy of oral anticoagulants These cephalosporins have vitamin K antagonistic activity, which adds to the action of oral anticoagulants. Monitor INR closely any significant t INR may require vitamin K therapy. If possible, use an alternative cephalosporin... 

ANTICOAGULANTS - ORAL BICALUTAMIDE t plasma concentrations of warfarin Bicalutamide displaces warfarin from protein-binding sites Monitor INR at least weekly until stable at initiation and discontinuation of concurrent therapy... 

NEOMYCIN ANTICOAGULANTS - ORAL Elevated prothrombin times and T risk of bleeding The mechanism is not fully understood however, it is thought that neomycin may 1 number of vitamin K-producing bacteria in the gastrointestinal tract and/or that the absorption of vitamin K may be 1 by the neomycin The INR should be monitored in all patients starting or stopping neomycin therapy. Patients more at risk are those with an inadequate diet... 

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