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Ambulatory Care Clinical Pharmacist, Wake Forest University Baptist Medical Center, Winston-Salem, NC 27157, 4506-1A Crowne Lake Circle, Jamestown, North Carolina 27282, fax 336/716-7771, dldixon{at}wfubmc.edu
Clinical Pharmacist Specialist, Pharmacy Department, Asheville Veterans Affairs Medical Center, Asheville, North Carolina
Senior Statistician, Adjunct Professor of Clinical Research, Clinical Research Department, Campbell University, Buies Creek, North Carolina
Published Online, November 27, 2007. www.theannals.com, DOI 10.1345/aph.1K412
Patients prescribed a treatment dose (1 mg/kg every 12 h) of enoxaparin for periprocedural bridging or when the international normalized ratio (INR) fell below 2.0 were identified. Patients were excluded when creatinine clearance was less than 30 mL/min, when body mass index was greater than 40 kg/m2, or when patients were nonadherent or missed appointments. Forty-nine patients represented 103 bridging episodes for procedures (n = 26) and subtherapeutic anticoagulation (n = 77). Charts from 2002-2006 were reviewed for documentation of embolism and bleeding. Major bleeding was defined as a hemoglobin decrease of at least 2.0 g/dL or blood transfusion of at least 2 units of packed red blood cells. Bleeding not meeting major bleed criteria was considered minor.
The mean age of patients having atrial (n = 21), mitral (n = 21), or both atrial and mitral (n = 7) mechanical valves was 65.9 years (range 55-81). Additional embolic risk factors included atrial fibrillation (n = 26), prior stroke (n = 12), and deep vein thrombosis (n = 1). American College of Chest Physicians recommendations were used to assess embolic risk.2 Procedure types included gastrointestinal (n = 11), dental (n = 6), urological (n = 5), orthopedic (n = 2), ophthalmologic (n = 1), and otolaryngologic (n = 1). Warfarin was withheld 4.6 ± 0.3 (mean ± SD) days preprocedure and enoxaparin was started 40.4 hours after warfarin discontinuation. Enoxaparin was stopped 22.1 ± 4.6 hours preprocedure, restarted the day after the procedure, and continued until the INR reached at least 2.0 (7.7 ± 3.3 days), with the assumption that patients with slightly subtherapeutic levels would quickly achieve therapeutic range. Therapy bridged for patients with subtherapeutic anticoagulation had an INR of 1.5 ± 0.2 at the time of bridging and was bridged to an INR of 2.0 or greater, thus requiring enoxaparin administration for 4.9 ± 2.9 days. Time to therapeutic range was longer for procedural bridging (12.4 ± 9.7 days) compared with that for subtherapeutic anticoagulation bridging (7.2 ± 5.9 days). Anti-Xa levels were not obtained for bridging episodes.
The overall bleeding rate was 11.6%. Major and minor bleeding rates were 1.9% and 9.7%, respectively (Table 1). Less bleeding occurred (p < 0.001) in the subtherapeutic anticoagulation group (5.2%) than in the procedural group (30.7%), which included a 26.9% minor bleeding rate. One major bleed requiring hospitalization occurred in each bridging category, neither of which resulted in death.
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Our study's major bleeding rate of 1.9% is comparable with that of other studies, which have reported rates as high as 6.7%.3 A minor bleeding rate of 9.7% was observed, which is also similar to that of other studies.4 It should be noted that 85% of the procedures evaluated in our study are commonly associated with minor bleeding (eg, dental, urological). We also found no documentation of embolism up to 30 days postbridging. Considering the severity of stroke and estimated incidence of periprocedural stroke (0.4-1.5%5), these data add to the literature supporting the use of enoxaparin in patients with mechanical heart valves.
Although our study was retrospective and lacked a comparator group, the data suggest that bridging high-risk patients during periods of subtherapeutic anticoagulation, as well as for periprocedural purposes, is safe. The remaining question is whether periodic inadequate anticoagulation exposes patients to an embolic risk warranting bridging. Additional studies evaluating embolic risk during short-term periods of subtherapeutic anticoagulation would assist in determining whether the embolic risk outweighs the potential bleed risk of LMWH bridging.
Footnotes
This material is the result of work supported with resources and the use of facilities at the Asheville Veterans Affairs Medical Center.
Parts of this study were presented at the American Society of Health-System Pharmacists Midyear Clinical Meeting in Anaheim, CA, December 3-7, 2006, and at the Southeastern Residency Conference in Athens, GA, April 26-27, 2007.
We express gratitude to Brenda Jamerson PharmD, Clinical Research Center Director and Associate Professor, Campbell University School of Pharmacy.
References
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