Prothrombin Times Outside the Therapeutic Range in Otherwise Stable Patients (FORESPEAK-0)
Warfarin is very effective for the prevention of blood clots (thrombosis). A test of coagulation, the prothrombin time (PT) is used to monitor the effect. The PT response to warfarin can fluctuate as a result of interactions with a large number of other drugs, food or herbal agents as well as for no apparent reason. Thus, frequent monitoring of the PT and dose adjustments according to the results are required. One third of our patients remain on the same maintenance dose over 6 months. However, also these patients sometimes have a PT result moderately outside the therapeutic range without any obvious explanation. Too short PTs may be due to missed dose(s) or more dark green vegetables in the diet. Too long PTs may be due to a course of antibiotic therapy or less dark green vegetables. Laboratory errors may also occur and can cause deviations in any direction. Most likely, unnoticed fluctuations in the PT occur as well between the time points of monitoring.
There are no guidelines on how to manage the treatment in this situation but there are some typical "behaviours".
Behavior A: Some physicians simply let the patient continue with the same dose. "It is extremely unlikely that the very temporary dose adjustment has any effect on the PT result 4 weeks later and this is a "cosmetic procedure"." Behavior B: Others recommend the patients to take ½ - 1 additional dose in case of short PT and to skip a dose or take half dose in case of long PT, and thereafter to continue with the usual dose. "The investigators need to quickly correct the temporary aberration in order to avoid thrombotic or bleeding complications the next few days.
This may seem like an issue of no importance. The investigators are however performing a series of studies to evaluate if these stable patients can be managed with blood tests less often than every 4 weeks. For that purpose it is important to know how often and why aberrant results occur, the implication and to what extent they can be ignored.
The investigators hypothesis is that in patients with very stable PT-results and unchanged dose for 3 months, should continue with exactly the same maintenance dose, even when the result unexpectedly is slightly above or below the therapeutic range. The investigators believe that most of these occasional PT-results outside the therapeutic range are due to laboratory errors, perhaps missed doses by the patient or temporary change in diet or medications.
|Study Design:||Allocation: Randomized
Endpoint Classification: Efficacy Study
Intervention Model: Parallel Assignment
Masking: Open Label
Primary Purpose: Treatment
|Official Title:||Management of Prothrombin Times Outside the Therapeutic Range in Patients on Warfarin and With Otherwise Stable Levels|
- Number of Patients With Prothrombin Time Results Within the Therapeutic Range After 2 Weeks [ Time Frame: 2 weeks ] [ Designated as safety issue: No ]The number of patients with "follow-up INRs" within the therapeutic range was compared for patients with a single dose skipped/reduced/added versus patients with no change of dose.
|Study Start Date:||July 2006|
|Study Completion Date:||April 2009|
|Primary Completion Date:||January 2009 (Final data collection date for primary outcome measure)|
Experimental: No change
Intervention Drug warfarin no change in the dose is performed
No change: Continue without any change in spite of prothrombin time outside the therapeutic range.
Other Name: Coumadin
Active Comparator: Change
Intervention Drug Warfarin One dose increased if subtherapeutic level; one dose deleted or reduced if supratherapeutic level
Change: Increase one dose in case prothrombin time is below the therapeutic range; delete or reduce one dose in case prothrombin time is above the therapeutic range.
Other Name: Coumadin
Thrombosis Service at HHS - General Hospital. This center monitors the warfarin treatment for 1300 patients in the region. These patient regularly go to a laboratory where they live. Test results (INR-results) are faxed to the Thrombosis Service, which calls the patient the same day to inform them of the results, how to continue dosing the warfarin and when to go for the following blood test.
|Thrombosis Service, HHS-General Hospital|
|Hamilton, Ontario, Canada, L8L 2X2|
|Principal Investigator:||Sam Schulman, MD, PhD||McMaster University|