[International normalized ratio (INR) for optimal anticoagulant therapy]

Optimal therapeutic ranges for an oral anticoagulant therapy has been discussed for many years. Prothrombin time, prothrombin time ratios (PTR) and thrombotest have been employed so far, but, recently, International Normalized Ratio of prothrombin time (PT-INR or INR) has been introduced. We investigated paying special interest to INR, the effectiveness of oral anticoagulant therapy in 170 prosthetic valve patients and in 157 patients with various cardiovascular diseases who received warfarin at two different centers. The thrombotest, prothrombin time and INR were measured at follow-up visits every month. Regarding the 170 patients with prosthetic valves with a mean follow-up period of 2.44 years, 9 thromboembolisms (TE) were reported. The average TT and INR values in TE-free patients among 101 in whom coagulability could be measured, were 21.1% and 1.73 respectively. The average TT and INR values in 5 patients with TE were 26.4% and 1.53 respectively and this was significantly (p < 0.01) higher (smaller) than in TE-free patients. 157 patients (mean age 55 +/- 12 y.o.) with various cardiovascular diseases (Table 2) were followed up for a mean of 4.9 +/- 3.2 years. As is seen in figure 4, mean INR values in TE patients were 1.28, in patients with bleeding complications 4.1, and in event free patients 2.07 respectively. In conclusion, with INR greater than 2.75, no thromboembolic complication occurred, but several hemorrhagic complications occurred at INR greater than 3. Therefore INR therapeutic ranges between 2.0-3.0 are recommendable both for the prevention of TE and bleeding complications.