Warfarin Sodium (Page 3 of 11)

Myocardial Infarction

WARIS (The Warfarin Re-Infarction Study) was a double-blind, randomized study of 1214 patients 2 to 4 weeks post-infarction treated with warfarin to a target INR of 2.8 to 4.8. [But note that a lower INR was achieved and increased bleeding was associated with INR’s above 4.0; (see DOSAGE AND ADMINISTRATION)]. The primary endpoint was a combination of total mortality and recurrent infarction. A secondary endpoint of cerebrovascular events was assessed. Mean follow-up of the patients was 37 months. The results for each endpoint separately, including an analysis of vascular death, are provided in the following table:

TABLE 3

Event

Warfarin

Placebo

RR

% Risk Reduction

(N=607)

(N=607)

(95% CI)

(p- value)

RR= Relative risk; Risk reduction = (I — RR); CI=Confidence interval; MI=Myocardial infarction; py = patient years

Total Patient Years of Follow-up 2018 1944
Total Mortality 94 (4.7/100 py) 123 (6.3/100 py) 0.76 (0.60, 0.97) 24 (p=0.030)
Vascular Death 82 (4.1/100 py) 105 (5.4/100 py) 0.78 (0.60, 1.02) 22 (p=0.068)
Recurrent MI 82 (4.1/100 py) 124 (6.4/100 py) 0.66 (0.51, 0.85) 34 (p=0.001)
Cerebrovascular Event 20 (1.0/100 py) 44 (2.3/100 py) 0.46 (0.28, 0.75) 54 (p=0.002)

WARIS II (The Warfarin, Aspirin, Re-Infarction Study) was an open-label randomized study of 3630 patients hospitalized for acute myocardial infarction treated with warfarin target INR 2.8 to 4.2, aspirin 160 mg/day, or warfarin target INR 2.0 to 2.5 plus aspirin 75 mg/day prior to hospital discharge. There were approximately four times as many major bleeding episodes in the two groups receiving warfarin than in the group receiving aspirin alone. Major bleeding episodes were not more frequent among patients receiving aspirin plus warfarin than among those receiving warfarin alone, but the incidence of minor bleeding episodes was higher in the combined therapy group. The primary endpoint was a composite of death, nonfatal reinfarction, or thromboembolic stroke. The mean duration of observation was approximately 4 years. The results for WARIS II are provided in the following table8:

TABLE 4 WARIS II — DISTRIBUTION OF SEPARATE EVENTS ACCORDING TO TREATMENT GROUP *
Event Aspirin (N=1206) Warfarin (N=1216) Aspirin plus Warfarin (N=1208) Rate Ratio (95% CI) p-value

ND = not determined.

*
CI denotes confidence interval.
The rate ratio is for aspirin plus warfarin as compared with aspirin.
The rate ratio is for warfarin as compared with aspirin.
§
Major bleeding episodes were defined as nonfatal cerebral hemorrhage or bleeding necessitating surgical intervention or blood transfusion.
Minor bleeding episodes were defined as non-cerebral hemorrhage not necessitating surgical intervention or blood transfusion.
No. of Events
Reinfarction 117 90 69 0.56 (0.41-0.78)0.74 (0.55-0.98) <0.001 0.03
Thromboembolic stroke 32 17 17 0.52 (0.28-0.98) 0.52 (0.28-0.97) 0.03 0.03
Major Bleeding § 8 33 28 3.35(ND) 4.00 (ND) ND ND
Minor Bleeding 39 103 133 3.21(ND) 2.55 (ND) ND ND
Death 92 96 95 0.82

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