Warfarin in atrial fibrillation: DISCUSSION(2)

The results from this cost-effectiveness analysis become even more dramatic when applied to the Canadian population. Using 1991 census data (the most recently available), a net savings to the health care system is realized when warfarin is used on indicated people. Up to 1.25% major complication rate will still result in a net savings (Tables 8-10). Similar results were also found in a Swedish study, indicating a net savings up to a 1.3% major bleeding complication rate. The critical value here is the rate of major bleeding which increases with age. buy flovent inhaler

The paiients in this meta-analysis were, on average, 70 years old. Patients 60 years of age and younger are considered to be at low risk for stroke and are generally not prescribed warfarin treatment. Other low risk individuals include those with lone atrial fibrillation and, perhaps more controversially, paroxysmal atrial fibrillation.

TABLE 8

Population statistics for Canada

Age Total population* Prevalence of atrial fibrillation^: n (%) Eligible for warfarin*
50-59 2,548,389 12,741 (0.5) 6370
60-69 2,249,875 40,497 (1.8) 20,248
70-79 1,436,675 68,960 (4.8) 20,688
80-89 566,280 49,832 (8.8)
Total eligible 47,307

*Census Canada 1991; fFramingham study (9); *Swedish study -50% eligibility except for 70- to 79-year-olds (only 30% eligible) (13); §Too high risk of bleeding (13)

TABLE 9

Potential total reduction of cardiovascular events* in Canada using warfarin

Stroke rateNo antithrombotic therapy @4. 35% Num ber o f strok2058 ies*
Warfarin @1.50% 710
Number of strokes prevented 1348
Major hemorrhage (%): 0.3 0.83 1.0 1.1 1.25 1.3
Number of hemorrhages: 142 393 473 520 591 615
Net reduction*: 1206 955 875 828 757 733

*Includes stroke and major bleed; fStroke rate is multiplied by warfarin eligible group (n=47,307); *Number of strokes prevented minus number of hemorrhages

TABLE 10

Net saving (cost) with warfarin therapy

Hemorrhage(%)0.3 # of people treated to prevent one stroke*39 Cost of treatment*$17,271.93 Savings*$10,228.07
0.83 50 $22,143.50 $5,356.50
1.0 54 $23,914.98 $3,585.02
1.1 57 $25,243.59 $2,256.41
1.25 62 $27,457.94 $42.06
1.3 65 $28,786.55 ($1,286.55)

*Reciprocal of reduction in rate of stroke;fNumber of people treated to prevent one stroke x cost of warfarin therapy; *Cost of stroke minus cost of warfarin treatment

Assessing the question of risk/ benefit is a formidable task. Some have suggested, using decision analysis, that the risk of bleeding must be at least six times more detrimental than emboli to justify withholding of anticoagulation. This analysis found major bleeding events to be fewer then embolic events (0.94% and 1.50%, respectively, in the warfarin group). However, when minor bleeding events are compared with embolic events, there is a 7.2-fold increase (10.85% ver sus 1.50%, respectively, in the warfarin group) in bleeding. This comparison may not be valid since minor bleeding events, as the name suggests, are not life threatening compared with the seriousness of an embolic event.

Category: Warfarin

Tags: Atrial fibrillation, cost-effectiveness, Economic analysis, Stroke, Warfarin

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