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Should we shorten treatment of DVT and PE to 3 months? Not yet.
Henry I. Bussey, Pharm.D., FCCP, FAHA
April, 2007
Reference: Campbell IA, Bentley DP, Prescott RJ, Routledge PA, Shetty HG, Williamson IJ. Anticoagulation for three versus six months in patients with deep vein thrombosis or pulmonary embolism, or both: randomised trial. BMJ. 2007 Mar 31;334(7595):674. Epub 2007 Feb 8.
Note: This study is being highlighted because it has been highly publicized as supporting 3 months rather that 6 months of treatment for initial idiopathic deep vein thrombosis (DVT) and/or pulmonary embolism (PE). Perhaps a more important interpretation is that the report supports the suggestion of others that the duration of anticoagulation beyond the initial 3 months should be determined based on risk stratification for recurrence of venous thromboembolism (VTE) - as reviewed previously on ClotCare at http://www.clotcare.com/clotcare/ddimercoumadindecision.aspx.
The following is a brief critique and summary of key points of this study.
The study randomized initial idiopathic DVT and/or PE patients to either three months (n = 369) or six months (n = 380) of anticoagulation therapy and followed both groups for a total period of 12 months (including the treatment phases). The results indicated little difference in benefit but an increase in bleeding with the longer term therapy.
A few of the limitations as well as a table of the results from this study follow:
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The primary endpoint was not recurrence of VTE (venous thromboembolic events) but rather the combined endpoint of death from DVT/PE, failure to resolve - or extension of - the clot, recurrence during treatment, recurrence after treatment, and major hemorrhage during treatment. Failure of the clot to resolve may not be related to duration of treatment and often is not a primary objective of treatment. Recurrence during treatment may be more a reflection of poor INR control rather than the duration of treatment.
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The VTE recurrence rates after treatment was stopped (presented graphically in the article) illustrate a pattern similar to that reported in earlier studies. At 9 months after treatment was stopped in the 3 month group, the post-treatment recurrence rate was approximately 7%. At 6 months after treatment was stopped in the 6 month treatment group, the recurrence rate was approaching 5%. The rates of VTE recurrence over time appeared to be similar such that a longer period of follow-up likely would yield similar recurrent event rates at 1 or 2 years after discontinuation of therapy (as has been reported by others).
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The 6-month group had both a higher level of recurrence and major bleeding during the first few months of therapy when treatment should have been equivalent. The higher bleeding rate in the 6-month treatment group did not appear to be due to the longer duration of treatment as all 8 events occurred in the first four months of therapy.
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The study design estimated that 2,400 patients would be needed to demonstrate a difference, but the study was concluded with a total enrollment of only 779 patients.
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Anticoagulation management was left to the patients' individual physicians and there is some suggestion in the paper that the duration of heparin therapy, the overlap with warfarin until the INR is stable, and the degree of INR control may not have been optimal (> 10% had one-third or fewer INRs in range).
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Summary of event rates
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Event
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3 mo. treatment gp. (n = 369)
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6 mo. treatment gp. (n = 380)
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Death from PE during or after tx.
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2
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3
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DVT/PE failed to resolve, extended, or recurred during treatment
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6
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10
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Events after treatment was stopped
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23
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16
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Fatal + non-fatal DVT/PE during and after tx.
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31 (8%)
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29 (8%)
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Maj. Bleeding (non-fatal)
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None
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8*
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Adverse outcome
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31 (8%)
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35 (9%)
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*All 8 maj. bleeds occurred in the first 4 months of treatment.
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