What Are the Potential Interferences Observed with the Use of Oral Anticoagulants?
Because the response to oral anticoagulants differs from patient to patient, the dosage should be closely monitored. The dosage response is influenced by both pharmacokinetic factors (differences in absorption) and pharmacodynamic factors (differences in the hemostatic response to several concentrations). In addition, technical factors can contribute to apparent variability in dosage response, such as inaccuracies in laboratory testing and poor patient compliance. Table. Drugs may modify the pharmacokinetics of warfarin by altering its metabolic clearance or by reducing its absorption Decrease anticoagulant effect (lower INR) Antacids Antiepileptic drugs: barbiturates, carbamazepine Antihistamines Antithyroid drugs Cholestyramine Rifampicin Vitamin K Increase anticoagulant effect (raise INR) Alcohol Allopurinol Amiodarone Anabolic steroids Antibiotics: erythromycin, metronidazole, quinolones, trimethoprimsulphamethoxazole; imidazole Antibiotics: isoniazid, high intravenous dose penicil
